| By Author | [ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | Other Symbols ] |
| By Title | [ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | Other Symbols ] |
| By Language |
|
Download this book: [ ASCII ] Look for this book on Amazon Tweet |
Title: Problems of Life and Mind. Second series: The Physical Basis of Mind
Author: Lewes, George Henry
Language: English
As this book started as an ASCII text book there are no pictures available.
*** Start of this LibraryBlog Digital Book "Problems of Life and Mind. Second series: The Physical Basis of Mind" ***
Transcriber’s Note
In PROBLEM I, CHAPTER III, Section 45 (originally page 38), chemical
formulas represent the numbers of atoms in a molecule with patterns
like this: C_{114}. Throughout this eBook, pairs of underscores enclose
italicized text, Small-caps text appears as ALL-CAPS, and pairs of
equals signs enclose boldface text.
Works by the same Author.
=PROBLEMS OF LIFE AND MIND. The Foundations of a Creed.= Two
Volumes. Octavo. Per volume, $3.00.
CONTENTS: The Method of Science and its Applications to
Metaphysics--The Rules of Philosophizing--Psychological
Principles--The Limitations of Knowledge--The Principles
of Certitude--From the Known to the Unknown--Matter and
Force--Force and Cause--The Absolute in the Correlations of
Feeling and Motion.
=THE STORY OF GOETHE’S LIFE.= New Edition. One volume. 16mo. With
Portrait. $1.50.
*.* _For sale by all Booksellers. Sent, post-paid, on receipt of price
by the Publishers,_
HOUGHTON, MIFFLIN & CO., BOSTON.
THE
PHYSICAL BASIS OF MIND.
With Illustrations.
_BEING THE SECOND SERIES_
OF
PROBLEMS OF LIFE AND MIND.
BY
GEORGE HENRY LEWES.
[Illustration: The Riverside Press.]
BOSTON AND NEW YORK:
HOUGHTON, MIFFLIN AND COMPANY.
The Riverside Press, Cambridge.
1891.
AUTHOR’S EDITION.
_From Advance Sheets._
_The Riverside Press, Cambridge, Mass., U. S. A._
Printed by H. O. Houghton & Company.
PREFACE.
The title indicates that this volume is restricted to the group of
material conditions which constitute the organism in relation to the
physical world--a group which furnishes the data for one half of the
psychologist’s quest; the other half being furnished by historical and
social conditions.
The Human Mind, so far as it is accessible to scientific inquiry, has
a twofold root, man being not only an animal organism but an unit in
the social organism; and hence the complete theory of its functions and
faculties must be sought in this twofold direction. This conception
(which has been declared “to amount to a revolution in Psychology”),
although slowly prepared by the growing conviction that Man could not
be isolated from Humanity, was first expounded in the opening volume of
these _Problems of Life and Mind_; at least, I am not aware that any
predecessor had seen _how_ the specially human faculties of Intellect
and Conscience were products of social factors co-operating with the
animal factors.
In considering the Physical Basis a large place must be assigned to
the mechanical and chemical relations which are involved in organic
functions; yet we have to recognize that this procedure of Analysis is
artificial and preparatory, that none of its results are final, none
represent the synthetic reality of _vital_ facts. Hence one leading
object of the following pages has been everywhere to substitute
the biological point of view for the metaphysical and mechanical
points of view which too often obstruct research--the one finding its
expression in spiritualist theories, the other in materialist theories;
both disregarding the plain principle that the first requisite in a
theory of biological phenomena must be to view them in the light of
biological conditions: in other words, to fix our gaze upon what passes
in the organism, and not on what may pass in the laboratory, where
the conditions are different. Analysis is a potent instrument, but
is too often relied on in forgetfulness of what constitutes its real
aid, and thus leads to a disregard of all those conditions which it
has artificially set aside. We see this in the tendency of anatomists
and physiologists to assign to _one_ element, in a complex cluster of
co-operants, the significance which properly belongs to that cluster:
as when the property of a tissue is placed exclusively in a single
element of that tissue, the function of an organ assigned to its chief
tissue, and a function of the organism to a single organ.
Another object has been to furnish the reader uninstructed in
physiology with such a general outline of the structure and functions
of the organism, and such details respecting the sentient mechanism,
as may awaken an interest in the study, and enable him to understand
the application of Physiology to Psychology. If he comes upon details
which can only interest specially educated students, or perhaps
only by them be really understood, he can pass over these details,
for their omission will not seriously affect the bearing of the
general principles. I have given the best I had to give; and must
leave each reader to find in it whatever may interest him. The uses
of books are first to stimulate inquiry by awakening an interest;
secondly, to clarify and classify the knowledge already gained from
direct contemplation of the phenomena. They are stimuli and aids to
observation and thought. They should never be allowed to see for us,
nor to think for us.
The volume contains four essays. The first, on the _Nature of Life_,
deals with the speciality of organic phenomena, as distinguished
from the inorganic. It sets forth the physiological principles which
Psychology must incessantly invoke. In the course of the exposition I
have incorporated several passages from four articles on Mr. Darwin’s
hypotheses, contributed to the _Fortnightly Review_ during the year
1868. I have also suggested a modification of the hypothesis of Natural
Selection, by extending to the _tissues and organs_ that principle of
competition which Mr. Darwin has so luminously applied to _organisms_.
Should this generalization of the “struggle for existence” be accepted,
it will answer many of the hitherto unanswerable objections.
The second essay is on the _Nervous Mechanism_, setting forth what is
known and what is inferred respecting the structure and properties of
that all-important system. If the sceptical and revolutionary attitude,
in presence of opinions currently held to be established truths,
surprises or pains the reader unprepared for such doubts, I can only
ask him to submit my statements to a similar scepticism, and confront
them with the ascertained evidence. After many years of laborious
investigation and meditation, the conclusion has slowly forced
itself upon me, that on this subject there is a “false persuasion of
knowledge” very fatal in its influence, because unhesitatingly adopted
as the ground of speculation both in Pathology and Psychology. This
persuasion is sustained because few are aware how much of what passes
for observation is in reality sheer hypothesis. I have had to point out
the great extent to which Imaginary Anatomy has been unsuspectingly
accepted; and hope to have done something towards raising a rational
misgiving in the student’s mind respecting “the superstition of the
nerve-cell”--a superstition which I freely confess to have shared in
for many years.
The third essay treats of _Animal Automatism_. Here the constant
insistance on the biological point of view, while it causes a rejection
of the mechanical theory, admits the fullest recognition of all the
mechanical relations involved in animal movements, and thus endeavors
to reconcile the contending schools. In this essay I have also
attempted a psychological solution of that much-debated question--the
relation between Body and Mind. This solution explains why physical
and mental phenomena must necessarily present to our apprehension
such profoundly diverse characters; and shows that Materialism, in
attempting to deduce the mental from the physical, puts into the
conclusion what the very terms have excluded from the premises;
whereas, on the hypothesis of a physical process being only the
objective aspect of a mental process, the attempt to interpret the one
by the other is as legitimate as the solution of a geometrical problem
by algebra.
In the final essay the _Reflex Theory_ is discussed; and here once
more the biological point of view rectifies the error of an analysis
which has led to the denial of Sensibility in reflex actions, because
that analysis has overlooked the necessary presence of the conditions
which determine Sensibility. In these chapters are reproduced several
passages from the _Physiology of Common Life_.
According to my original intention, this volume was to have included an
exposition of the part I conceive the brain to play in physiological
and psychological processes, but that must be postponed until it can be
accompanied by a survey of psychological processes which would render
the exposition more intelligible.
THE PRIORY, March, 1877.
CONTENTS.
PROBLEM I. THE NATURE OF LIFE.
CHAPTER I.
PAGE
THE PROBLEM STATED 3
(_The Position of Biology_) 4
(_Organisms_) 8
(_Vital Force_) 14
(_Vital Force controlling Physical and Chemical Forces_) 16
CHAPTER II.
DEFINITIONS OF LIFE 24
CHAPTER III.
ORGANISM, ORGANIZATION, AND ORGANIC SUBSTANCE 37
(_Organism and Medium_) 45
(_The Hypothesis of Germinal Matter_) 57
(_Organisms and Machines_) 67
CHAPTER IV.
THE PROPERTIES AND FUNCTIONS 70
(_Does the Function determine the Organ?_) 78
CHAPTER V.
EVOLUTION 89
(_Natural Selection and Organic Affinity_) 115
(_Recapitulation_) 152
PROBLEM II. THE NERVOUS MECHANISM.
CHAPTER I.
SURVEY OF THE SYSTEM, 157
(_The Early Forms of Nerve-Centres_), 168
(_The Peripheral System_), 171
(_Ganglia and Centres_), 172
CHAPTER II.
THE FUNCTIONAL RELATIONS OF THE NERVOUS SYSTEM, 176
CHAPTER III.
NEURILITY, 189
(_Origins of Nerve-Force_), 201
(_The Hypothesis of Specific Energies_), 207
CHAPTER IV.
SENSIBILITY, 211
CHAPTER V.
ACTION WITHOUT NERVE-CENTRES, 227
CHAPTER VI.
WHAT IS TAUGHT BY EMBRYOLOGY?, 237
CHAPTER VII.
THE ELEMENTARY STRUCTURE OF THE NERVOUS SYSTEM, 251
(_Difficulties of the Investigation_), 252
(_The Nerve-Cell_), 258
(_The Nerves_), 270
(_The Neuroglia_), 273
(_The Relations of the Organites_), 278
(_Recapitulation_), 299
CHAPTER VIII.
THE LAWS OF NERVOUS ACTIVITY 310
(_The Energy of Neurility_) 311
(_The Propagation of Excitation_) 314
(_Stimuli_) 321
(_Stimulation_) 324
(_The Law of Discharge_) 326
(_The Law of Arrest_) 333
(_The Hypothesis of Inhibitory Centres_) 336
(_Anatomical Interpretations of the Laws_) 339
PROBLEM III. ANIMAL AUTOMATISM.
CHAPTER I.
THE COURSE OF MODERN THOUGHT 345
CHAPTER II.
THE VITAL MECHANISM 363
CHAPTER III.
THE RELATION OF BODY AND MIND 376
CHAPTER IV.
CONSCIOUSNESS AND UNCONSCIOUSNESS 399
CHAPTER V.
VOLUNTARY AND INVOLUNTARY ACTIONS 415
CHAPTER VI.
THE PROBLEM STATED 431
CHAPTER VII.
IS FEELING AN AGENT? 440
PROBLEM IV. THE REFLEX THEORY.
CHAPTER I.
THE PROBLEM STATED 467
CHAPTER II.
DEDUCTIONS FROM GENERAL LAWS 490
CHAPTER III.
INDUCTIONS FROM PARTICULAR OBSERVATIONS 509
(_Cerebral Reflexes_) 511
(_Discrimination_) 520
(_Memory_) 522
(_Instinct_) 522
(_The Acquisition of Instinct_) 536
(_Acquisition_) 546
CHAPTER IV.
NEGATIVE INDUCTIONS 550
PROBLEM I.
THE NATURE OF LIFE.
“La Physiologie a pour but d’exposer les phénomènes de la vie
humaine et les conditions d’où ils dépendant. Pour y arriver
d’une manière sûre, il faut nécessairement avant tout déterminer
quels sont les phénomènes qu’on désigne sous le nom de vie en
général. C’est pourquoi la première chose à faire est d’étudier
les propriétés générales du corps qu’on appelle organiques ou
vivans.”--TIEDEMANN, _Traité de Physiologie de l’Homme_, I. 2.
“Some weak and inexperienced persons vainly seek by dialectics and
far-fetched arguments either to upset or establish things that are
only to be founded on anatomical demonstration and believed on the
evidence of the senses. He who truly desires to be informed of the
question in hand must be held bound either to look for himself, or
to take on trust the conclusions to which they who have looked have
come.”--HARVEY, _Second Dissertation to Riolan_.
THE NATURE OF LIFE.
CHAPTER I.
THE PROBLEM STATED.
1. Although for convenience we use the terms Life and Mind as
representing distinct orders of phenomena, the one objective and the
other subjective, and although for centuries they have designated
distinct entities, or forces having different substrata, we may now
consider it sufficiently acknowledged among scientific thinkers that
every problem of Mind is necessarily a problem of Life, referring to
one special group of vital activities. It is enough that Mind is never
manifested except in a living organism to make us seek in an analysis
of organic phenomena for the material conditions of every mental fact.
Mental phenomena when observed in others, although interpretable by our
consciousness of what is passing in ourselves, can only be objective
phenomena of the vital organism.
2. On this ground, if on this alone, an acquaintance with the
general principles of structure and function is indispensable to
the psychologist; although only of late years has this been fully
recognized, so that men profoundly ignorant of the organism have had
no hesitation in theorizing on its highest functions. In saying that
such knowledge is indispensable, I do not mean that in the absence
of such knowledge a man is debarred from understanding much of the
results reached by investigators, nor that he may not himself make
useful observations and classifications of psychological facts. It is
possible to read books on Natural History with intelligence and profit,
and even to make good observations, without a scientific groundwork of
biological instruction; and it is possible to arrive at empirical facts
of hygiene and medical treatment without any physiological instruction.
But in all three cases the absence of a scientific basis will render
the knowledge fragmentary and incomplete; and this ought to deter
every one from offering an opinion on debatable questions which pass
beyond the limit of subjective observations. The psychologist who has
not prepared himself by a study of the organism has no more right to
be heard on the genesis of the psychical states, or of the relations
between body and mind, than one of the laity has a right to be heard on
a question of medical treatment.
THE POSITION OF BIOLOGY.
3. Science is the systematic classification of Experience. It
postulates unity of Existence with great varieties in the Modes of
Existence; assuming that there is one Matter everywhere the same,
under great diversities in the complications of its elements. The
distinction of Modes is not less indispensable than the identification
of the elements. These Modes range themselves under three supreme
heads: Force, Life, Mind. Under the first, range the general properties
exhibited by _all_ substances; under the second, the general properties
exhibited by _organized_ substances; under the third, the general
properties exhibited by organized _animal_ substances. The first
class is subdivided into _Physics_, celestial and terrestrial, and
_Chemistry_. Physics treats of substances which move as masses,
or which vibrate and rotate as molecules, without undergoing any
appreciable change of structural integrity; they show changes of
_position_ and _state_, without corresponding changes in their
elements. Chemistry treats of substances which undergo molecular
changes of composition _destructive_ of their integrity. Thus the blow
which simply moves one body, or makes it vibrate, explodes another. The
friction which alters the temperature and electrical state of a bit of
glass, ignites a bit of phosphorus, and so destroys its integrity of
structure, converting phosphorus into phosphoric acid.
4. The second class, while exhibiting both physical and chemical
properties, is markedly distinguished by the addition of properties
called vital. Their peculiarity consists in this: they undergo
molecular changes of composition and decomposition which are
simultaneous, and _by this simultaneity preserve their integrity of
structure_. They change their state, and their elements, yet preserve
their unity, and even when differentiating continue specific. Unlike
all other bodies, the organized are born, grow, develop, and decay,
through a prescribed series of graduated evolutions, each stage being
the indispensable condition of its successor, no stage ever appearing
except in its serial order.
5. The third class, while exhibiting all the characteristics of the
two preceding classes, is specialized by the addition of a totally
new property, called Sensibility, which subjectively is Feeling. Here
organized substance has become animal substance, and Vegetality has
been developed into Animality by the addition of new factors,--new
complexities of the elementary forces. Many, if not most, philosophers
postulate an entirely new Existence, and not simply a new Mode, to
account for the manifestations of Mind; they refuse to acknowledge
it to be a vital manifestation, they demand that to Life be added a
separate substratum, the Soul. This is not a point to be discussed
here. We may be content with the assertion that however great the
phenomenal difference between Humanity and Animality (a difference we
shall hereafter see to be the expression of a new factor, namely, the
social factor), nevertheless the distinctive attribute of Sensibility,
out of which rise Emotion and Cognition, marks the inseparable
_kinship_ of mental with vital phenomena.
Thus all the various Modes of Existence may, at least in their
objective aspect, be ranged under the two divisions of Inorganic and
Organic,--Non-living and Living,--and these are respectively the
objects of the cosmological and the biological sciences.
6. The various sciences in their serial development develop the
whole art of Method. Mathematics develops abstraction, deduction,
and definition; Astronomy abstraction, deduction, and observation;
Physics adds experiment; Chemistry adds nomenclature; Biology adds
classification, and for the first time brings into prominence the
important notion of _conditions of existence_, and the variation
of phenomena under varying conditions: so that the relation of the
organism to its medium is one never to be left out of sight. In
Biology also clearly emerges for the first time what I regard as the
true notion of causality, namely, the _procession_ of causes,--the
combination of factors in the product, and not an _ab extra_
determination of the product. In Vitality and Sensibility we are made
aware that the causes are _in_ and not _outside_ the organism; that
the organic effect is the organic cause in operation; that there is
autonomy but no autocracy; the effect issues as a resultant of the
co-operating conditions. In Sociology, finally, we see brought into
prominence the _historical conditions of existence_. From the due
appreciation of the conditions of existence, material and historical,
we seize the true significance of the principle of Relativity.
7. Having thus indicated the series of the abstract sciences we have
now to consider more closely the character of Biology. The term was
proposed independently yet simultaneously in Germany and France, in
the year 1802, by Treviranus and Lamarck, to express “the study of the
forms and phenomena of Life, the conditions and laws by which these
exist, and the causes which produce them.” Yet only of late years has
it gained general acceptance in France and England. The term Cosmology,
for what are usually called the Physical Sciences, has not yet come
into general use, although its appropriateness must eventually secure
its recognition.
Biology,--the abstract science of Life,--embracing the whole organic
world, includes Vegetality, Animality, and Humanity; the biological
sciences are Phytology, Zoölogy, and Anthropology. Each of the
sciences has its cardinal divisions, statical and dynamical, namely,
Morphology--the science of form,--and Physiology--the science of
function.
Morphology embraces--1°, _Anatomy_, i. e. the description of the parts
then and there present in the organism; and these parts, or organs, are
further described by the enumeration of their constituent tissues and
elements; and of these again the proximate principles, so far as they
can be isolated without chemical decomposition. 2°, _Organogeny_, i. e.
the history of the evolution of organs and tissues.
Physiology embraces the properties and functions of the tissues and
organs--the primary conditions of Growth and Development out of
which rise the higher functions bringing the organism into active
relation with the surrounding medium. The first group of properties
and functions are called those of vegetal, or organic life; the second
those of animal, or relative life.
ORGANISMS.
8. It will be needful to fix with precision the terms, Organism, Life,
Property, and Function.
An organism, although usually signifying a more or less complex unity
of organs, because the structures which first attracted scientific
attention were all thus markedly distinguished from inorganic
bodies, has by the gradual extensions of research been necessarily
generalized, till it now stands for any organized substance capable of
independent vitality: in other words, any substance having the specific
combination of elements which manifests the serial phenomena of growth,
development, and decay. There are organisms that have no differentiated
organs. Thus a microscopic formless lump of semifluid jelly-like
substance (Protoplasm) is called an organism, because it feeds itself,
and reproduces itself. There are advantages and disadvantages in such
extensions of terms. These are notable in the parallel extension of
the term Life, which originally expressing only the complex activities
of complex organisms, has come to express the simplest activities of
protoplasm. Thus a Monad is an organism; a Cell is an organism; a Plant
is an organism; a Man is an organism. And each of these organisms is
said to have its Life, because
“Through all the mighty commonwealth of things
Up from the creeping worm to sovereign man”[1]
there is one fundamental group of conditions, one organized substance,
one vitality.
Obviously this unity is an abstraction. In reality, the life manifested
in the Man is _not_ the life manifested in the Monad: he has Functions
and Faculties which the Monad has no trace of; and if the two organisms
have certain vital characteristics in common, this unity is only
recognized in an _ideal construction_ which lets drop all concrete
differences. The Life is different when the organism is different.
Hence any definition of Life would be manifestly insufficient which
while it expressed the activities of the Monad left unexpressed the
conspicuous and important activities of higher organisms. A sundial
and a repeater will each record the successive positions of the sun
in the heavens; but although both are instruments for marking time,
the sundial will not do the work of the repeater; the complexity and
delicacy of the watch mechanism are necessary for its more varied and
delicate uses. A semifluid bit of protoplasm will feed itself; but it
will not feed and sustain a complex animal; nor will it feel and think.
9. Neglect of this point has caused frequent confusion in the attempts
to give satisfactory definitions. Biologists ought to have been warned
by the fact that some of the most widely accepted definitions exclude
the most conspicuous phenomena of Life, and are only applicable to the
vegetable world, or to the vegetal processes in the animal world. A
definition, however abstract, should not exclude essential characters.
The general consent of mankind has made Life synonymous with Mode of
Existence. By the life of an animal is meant the existence of that
animal; when dead the _animal_ no longer exists; the substances of
which the organism was composed exist, but under another mode; their
connexus is altered, and the organism vanishes in the alteration.
It is a serious mistake to call the corpse an organism; for that
_special_ combination which constituted the organism is not present in
the corpse. This misconception misleads some speculative minds into
assigning life to the universe. The universe assuredly exists, but it
does not live; its existence can only be identified with life, such as
we observe in organisms, by a complete obliteration of the speciality
which the term Life is meant to designate. Yet many have not only
pleased themselves with such a conception, but have conceived the
universe to be an organism fashioned, directed, and sustained by a soul
like that of man--the _anima mundi_. This is to violate all scientific
canons. The life of a plant-organism is not the same as the life of an
animal-organism; the life of an animal-organism is not the same as the
life of a human-organism; nor can the life of a human-organism be the
same as the life of the world-organism. The unity of Existences does
not obliterate the variety of Modes; yet it is the speciality of each
Mode which Science investigates; to some of these Modes the term Life
is consistently applied, to others not; and if we merge them all in a
common term, we must then invent a new term to designate the Modes now
included under Life.
10. In resisting this unwarrantable extension of the term I am not
only pointing to a speculative error, but also to a serious biological
error common in both spiritualist and materialist schools, namely
that of assigning Life to other than organic agencies. Instead of
recognizing the speciality of this Mode of Existence as dependent on
a speciality of the organic conditions, the spiritualist assigns Life
to some extra-organic Vital Principle, the materialist assigns it to
some inorganic agent--physical or chemical. Waiving for the present all
discussion of Vitalism, let us consider in what sense we must separate
organic from all inorganic phenomena.
11. There is a distinction between inorganic and organic which may
fitly be called radical: it lies at the root of the phenomena, and must
be accepted as an ultimate fact, although the synthesis on which it
depends is analytically reducible to a complication of more primitive
conditions. It has been already indicated in § 5. All organisms above
the very simplest are syntheses Of three terms: Structure, Aliment,
and Instrument. Crystals, like all other anorganisms have structure,
and in a certain sense they may be said to grow (_Mineralia crescunt_),
though the growth is by _increase_ and not by _modification_:[2]
the motherlye, which is the food of the crystal, is never brought
to the crystal, nor prepared for it, by any instrumental agency of
the crystal. Organisms are exclusively instrumental; the organ is an
instrument. The structural integrity of an organism is thus preserved
through an alimentation which is effected through special instruments.
Nothing like this is visible in anorganisms.
The increase of a crystal is further distinguishable from the growth
of an organism, in the fact Of its being simple accretion without
development; and the structure of the crystal is distinguishable from
that of an organism in the fact that its integrity is preserved by
the _exclusion_ of all molecular change, and not by the simultaneous
changes of molecular decomposition and recomposition. Inorganic
substances are sometimes as unstable as organic, sometimes even more
unstable; but their instability is the source of their structural
destruction--they change into other species; whereas the instability
of _organized_ substances (_not_ of organic) is the source of their
structural integrity: the tissue is renovated, and its renovation is a
consequence of its waste.
12. But while the distinction is thus radical, when we view the
organism from the _real_--that is, from the synthetic point of view--we
must also urge the validity of the analytical point of view, which
seizes on the conditions here complicated in a special group, and
declares these conditions to be severally recognizable equally in
anorganisms and in organisms. All the fundamental properties of Matter
are recognizable in organized Matter. The elementary substances and
forces familiar to physicists and chemists are the materials of the
biologist; nor has there been found a single organic substance, however
special, that is not reducible to inorganic elements. We see, then,
that organized Matter is only a special combination of that which in
_other_ combinations presents chemical and physical phenomena; and we
are prepared to find Chemistry and Physics indispensable aids in our
analysis of organic phenomena. Aids, but only aids; indispensable, but
insufficient.
13. There is therefore an ambiguity in the common statement that
organized matter is not _ordinary_ matter. Indisputable in one sense,
this is eminently disputable when it is interpreted as evidence of
a peculiar Vital Force “wholly unallied with the primary energy of
Motion.” If by “ordinary matter” be meant earths, crystals, gases,
vapors, then assuredly organized matter is not ordinary. “Between the
_living_ state of matter and its _non-living_ state,” says Dr. Beale,
“there is an absolute and irreconcilable difference; so far from our
being able to demonstrate that the non-living passes by gradations
into or gradually assumes the scale or condition of the _living_, the
transition is sudden and abrupt, and matter already in the living
state may pass into the non-living condition in the same sudden and
complete manner.”[3] The ambiguity here is sensible in the parallel
case of the difference between crystallizable and coagulable matter, or
between one crystal and another. If we can decompose the organic into
the inorganic, this shows that the elements of the one are elements
of the other; and if we are not yet able to recompose the inorganic
elements into organic matter (not at least in its more complex forms),
may this not be due to the fact that we are ignorant of the proximate
synthesis, ignorant of the precise way in which the elements are
combined? I may have every individual part of a machine before me, but
unless I know the proper position of each, I cannot with the parts
reconstruct the machine. Indeed the very common argument on which so
much stress is laid in favor of some mysterious Principle as the source
of organic phenomena, namely, that human skill is hopelessly baffled in
the attempt to make organic substances, still more a living cell, is
futile. Men can make machines, it is said, but not organisms, _ergo_
organisms must have a spiritual origin. But the fact is that no man can
make a machine, _unless_ he take advantage of the immense traditions of
our race, and apply the skill of millions who have worked and thought
before him, slowly and tentatively discovering the necessary means
of mechanical effect. The greatest thinker, or the deepest scholar,
who did not place himself in the line of the tradition, and learn the
principles of mechanism, and the properties of the materials, would be
as incapable of making a watch, as the physiologist now is of making
a cell. But the skill of man has already succeeded in making many
organic substances, and will perhaps eventually succeed in making a
cell, certainly will, if ever the special synthesis which binds the
elements together should be discovered. Not that such a discovery would
alter the position of Biology in relation to Chemistry. The making of
albumen, nay, the construction of an organism in the laboratory, would
not in the least affect the foundation of Biology, would not obliterate
the radical difference between organisms and anorganisms. It is the
speciality of organic phenomena which gives them a special place,
although the speciality may only be due to a complication of general
agencies.
VITAL FORCE.
14. A similar ambiguity to that of the phrase “ordinary matter” lies
in the equally common phrase “Vital Force,” which is used to designate
a special group of agencies, and is then made to designate an agent
which has no kinship with the general group; that is to say, instead of
being employed in its real signification--that which alone represents
our knowledge--as the abstract statical expression of the complex
conditions necessary to the manifestation of vital phenomena, or as
the abstract dynamical expression of the phenomena themselves, it
is employed as an expression of their unknown Cause, which, because
unknown, is dissociated from the known conditions, and erected into
a mysterious Principle, having no kinship with Matter. In the first
sense the term is a shorthand symbol of what is known and inferred.
The known conditions are the relations of an organism and its medium,
the organism being the union of various substances all of which have
their peculiar properties when isolated; properties that disappear
in the union, and are replaced by others, which result from the
combination--as the properties of chlorine and sodium all disappear in
the sea-salt which results from their union; or as the properties of
oxygen and the properties of hydrogen disappear and are replaced by the
properties of water. When therefore Vital Force is said to be exalted
or depressed, the phrase has rational interpretation in the alteration
which has taken place in one or more of the conditions, internal and
external: a change in the tissues, the plasma, or the environment,
exalts or depresses the energy of the vital manifestations; and to
suppose that this is effected through the agency of some extra-organic
Principle is a purely gratuitous fiction.
15. That we are ignorant of one or more of the indispensable conditions
symbolized in the abstract term Vitality or Vital Force, is no reason
for quitting the secure though difficult path of Observation, and
rushing into the facile but delusive path of Fiction, which proposes
metempirical Agents (in the shape of Vital and Psychical Principles)
to solve the problems of Life and Mind. We may employ the term Vital
Force to label our observations, together with all that still remains
unobserved; and we are bound to recognize the line which separates
observation from inference, what is proved from what is inferred;
but while marking the limits of the known, we are not to displace
the known in favor of the unknown. It is said that because of our
ignorance we must assume these causes of Life and Mind to be _unallied_
with known material causes, and belonging to a different order of
existences. This is to convert ignorance into a proof; and not only
so, but to allow what we do not know to displace what we do know. The
organicist is ready to admit that much has still to be discovered; the
vitalist, taking his stand upon this unknown, denies that what has been
discovered is really important, and declares that the real agent is
wholly unallied to it. How _can_ he know this?
He does not know it; he assumes it; and the chief evidence he adduces
is that the ordinary laws of inorganic matter are incapable of
explaining the phenomena of organized matter; and that physical and
chemical forces are controlled by vital force. I accept both these
positions, stripping them, however, of their ambiguities. The laws of
ordinary matter are clearly incompetent in the case of matter which is
not ordinary, but _specialized_ in organisms; and when we come to treat
of Materialism we shall see how unscientific have been the hypotheses
which disregard the distinction. The question of control is too
interesting and important to be passed over here.
VITAL FORCE CONTROLLING PHYSICAL AND CHEMICAL FORCES.
16. The facts relied on by the vitalists are facts which every
organicist will emphasize, though he will interpret them differently.
When, for example, it is said that “Life resists the effect of
mechanical friction,” and the proof adduced is the fact that the
friction which will thin and wear away a dead body is actually the
cause of the thickening of a living--the skin of a laborer’s hand
being thickened by his labor; the explanation is not that Life, an
extra-organic agent, “resists mechanical friction”--for the mechanical
effect is _not_ resisted (the skin is rubbed off the rower’s hand
sooner than the wood is rubbed off the oar)--but that Life, i. e.
organic activity repairs the waste of tissue.
17. Again, although many of the physical and chemical processes which
invariably take place under the influences to which the substances
are subjected out of the organism, will not take place at all, or
will take place in different degrees, when the substances are in the
organism, this is important as an argument against the notion of vital
_phenomena_ being deducible from physical and chemical _laws_, but is
valueless as evidence in favor of an extra-organic agent. Let us glance
at one or two striking examples.
18. No experimental inquirer can have failed to observe the often
contradictory results which seemingly unimportant variations in the
conditions bring about; no one can have failed to observe what are
called chemical affinities wholly frustrated by vital conditions. Even
the ordinary laws of Diffusion are not always followed in the organism.
The Amœba, though semifluid, resists diffusion when alive; but when it
dies it swells and bursts by osmosis. The exchange of gases does not
take place in the tissues, precisely as in our retorts. The _living_
muscle respires, that is, takes up oxygen and gives out carbonic
acid, not on the principle of simple diffusion, but by two separable
physiological processes. The carbonic acid is given out, even when
there is no oxygen whatever present in the atmosphere, and its place
may then be supplied by hydrogen; and this physiological process is so
different from the physical process which goes on in the dead muscle
(the result of putrefaction), that it has been proved by Ranke to go
on when the temperature is so low that all putrefaction is arrested.
The same experimenter finds[4] that whereas living nerve will take up,
by imbibition, 10 per cent of potash salts, it will not take up 1 per
cent of soda salts, presented in equal concentration; and he points
to the general fact that the absorption of inorganic substances does
_not_ take place according to the simple laws of diffusion, but that
living tissues have special laws, the nerve, for instance, having
a greater affinity for neutral potash salts than for neutral soda
salts. Let me add, by way of anticipating the probable argument that
may urge this in favor of Vital Principle which is lightly credited
with the prescience of final causes, that so far from this “elective
affinity” of the tissues being intelligent and always favorable,
Ranke’s experiments unequivocally show that it is more active towards
destructive, poisonous substances, than towards the reparative,
alimentary substances; which is indeed consistent with the familiar
experience that poisons are more readily absorbed than foods, when both
are brought to the tissues. Thus it is well known that of all the salts
the sulphate of copper is that which plants most readily absorb--and
it kills them. The special affinities disappear as the vitality
disappears, and dying plants absorb all salts equally.
19. The more the organism is studied, the more evident it will become
that the simple laws of diffusion, as presented in anorganisms rarely
if ever take effect in tissues; in other words, what is called
Imbibition in Physics is the somewhat different process of Absorption
in Physiology.[5] The difference is notable in this capital fact, that
whereas the physical diffusion of liquids and gases is determined
by differences of density, the physiological absorption of liquids
and gases is determined by the molecular organization of the tissue,
which is perfectly indifferent to, and resists the entrance of, all
substances incapable of entering into organic combination, either as
aliment or poison. A curious example of the indifference of organized
substances to some external influences and their reaction upon others,
is the impossibility of provoking ciliary movement in an epithelial
cell, during repose, by any electrical, mechanical, or chemical stimuli
except potash and soda. Virchow discovered that a minute quantity of
either of these, added to the water in which the cell floated, at once
called forth the ciliary movements.
20. The true meaning of the resistance of Vitality to ordinary chemical
affinity is, that the conditions involved in the phenomena of Vitality
are not the conditions involved in the phenomena of Chemistry; in other
words, that in the living organism the substances are placed under
conditions different from those in which we observe these substances
when their chemical affinities are displayed in anorganisms. But we
need not go beyond the laboratory to see abundant examples of this
so-called resistance to chemical affinity, when the conditions are
altered. The decomposition of carbonates by tartaric acid is a chemical
process which is wholly resisted if alcohol instead of water be the
solvent employed. The union of sulphur with lead is said to be due
to the affinity of the one for the other; but no one supposes this
affinity to be irrespective of conditions, or that the union will take
place when any one of these conditions is absent. If we fuse a compound
of lead and iron in a crucible containing sulphur, we find it is the
iron, and not the lead, which unites with the sulphur; yet we do not
conclude that there is a Crucible Principle which frustrates chemical
affinity and resists the union of sulphur and lead; we simply conclude
that the presence of the iron is a condition which prevents the
combination of the sulphur with the lead: not until all the iron has
taken up its definite proportion of sulphur will the affinity of the
lead come into play. This is but another illustration of the law that
_effects are processions of their causes_, summations of the conditions
of their existence. If the fire burns no hole in the teakettle so long
as there is water to conduct the heat away, this is not due to any
principle more mysterious than the presence of a readily conducting
water.[6]
21. In accordance with the law of Causation just mentioned, which
has been expounded in detail in our First Series (Vol. II. p. 335),
the special combinations of Matter in organisms must present special
phenomena. Therefore since the province of Biology is that of
explaining organic phenomena by means of their organic conditions,
it must be radically distinguished from the provinces of Physics and
Chemistry, which treat not of organized but of inorganic matter. It
is idle, it is worse, for it is misleading, to personify the organic
conditions, known and inferred, in a Vital Principle; idle, because we
might with equal propriety personify the conditions of crystallization
in a Crystal Principle; misleading, because the artifice is quickly
dropped out of sight, and the abstract term then becomes accepted as
an entity, supposed to create or rule the phenomena it was invented to
express.
22. Inquirers are but too apt to misconceive the value of Analysis,
which is an artifice of Method indispensable to research, though
needing the complementary rectification by Synthesis before a real
explanation can be reached. Analysis decomposes the actual fact into
ideal factors, separates the group into its components, and considers
each of these, not as it exists in the group, in the reality, but as
it exists when theoretically detached from the others. The oxygen
and hydrogen into which water is decomposed did not exist as these
gases in the water; the albumen and phosphate we extract from a nerve
did not exist _as_ isolated albumen and phosphate in the nerve, they
were molecularly combined. In like manner the physical and chemical
processes which may analytically be inferred in vital processes do
not really take place in the same way as out of the organism. The
real process is always a vital process, and must be explained by the
synthesis of all the co-operant conditions. The laws of Physics and
Chemistry formulate abstract expressions of phenomena, wherever and
whenever these appear, without reference to the _modes of production_;
and in _this_ sense the movement of a limb is no less a case of
Dynamics than the movement of a pulley--the decomposition of a tissue
is a case of Chemistry no less than the decomposition of a carbonate;
the electromotor phenomena observed in muscle are as purely physical
as those observed in a telegraph. But when a biologist has to explain
the movements of the limbs, or the decompositions of tissues, he has
to deal with the phenomena and their modes of production, he has
a particular group before him, and must leave out nothing that is
characteristic of it. The movements of the pulley do not depend on
Contractility and Sensibility, which in turn depend on Nutrition. The
decomposition of the carbonate does not depend on conditions resembling
those of a living tissue. Vaucanson’s duck was surprisingly like a
living duck in many of its movements; but in none of its actions was
there any real similarity to the actions of a bird, because the machine
was unlike an organism in action. The antithesis of mechanism and
organism will be treated of in § 78.
23. We conclude, then, that defining physical phenomena as the
movements which take place _without_ change of structure, and chemical
phenomena as the movements _with_ change of structure, although
both classes may be said to take place in the organism, and to be
the primary conditions on which organic phenomena depend, they do
not embrace the whole of the conditions, nor are the sciences which
formulate them capable of formulating either the special phenomena
characteristic of organisms or their special modes of production. The
biologist will employ chemical and physical analysis as an essential
part of his method; but he will always rectify what is artificial in
this procedure, by subordinating the laws of Physics and Chemistry
to the laws of Biology revealed in the synthetic observation of
the organism as a whole. The rectification, here insisted on, will
be recognized as peculiarly urgent in Psychology, which has greatly
suffered from the misdirection of Analysis.
24. No one will misunderstand this specialization of Biology to mean
a separation of Life from the series of objective phenomena, and
the introduction of a new entity; the specialization points to a
Mode of Existence. All classifications are artifices, but they have
their objective grounds; the ground of difference on which Biology
is separated from Chemistry and Physics, though all three may be
merged in a common identity, is such as to justify the term radical.
A vital process is no more to be considered physico-chemical, because
physico-chemical conditions are presupposed in it, than a feeling is
to be considered a nutritive process, because Nutrition is presupposed
in all Feeling. Organic substances have been made by chemists, and
inorganic “cells” have also been made; but these substances were not
organized, these “cells” would not live. The germ-cell is the workshop
of generation, the secreting-cell the workshop of secretion, the
muscle-cell the workshop of contraction. What is required over and
above organic substances and cell-forms, is that special state called
_organization_. See § 49.
Those who contemplate the manifestations without also taking into
account their modes of production may see nothing but physico-chemical
facts in vital facts. It is by a similar limitation of the point of
view that Vitality is often confounded with Movement, and portions
of organic matter are said to live, simply on the evidence of their
movements.[7]
CHAPTER II.
DEFINITIONS OF LIFE.
25. Biology, the science of Life, being thus assigned its place in the
hierarchy of objective laws, we now proceed to consider what the term
Life symbolizes.
By a large preliminary simplification, Life may be defined as _the
mode of existence of an organism in relation to its medium_. To render
this of any value, however, a clear conception of the organism is
first indispensable; and this must be preceded by an examination of
the various attempts to define life in anticipation of such a clear
conception.
26. Every phenomenon, or group of phenomena, may be viewed under
two aspects--the _statical_, which considers the conditions of
existence; and the _dynamical_, which considers these conditions in
their resultant,--in their _action_. The statical definition of Life
will express the connexus of the properties of organized substance,
all those conditions, of matter, form, and texture, and of relation
to external forces, on which the organism depends. These various
conditions, condensed into a single symbol, constitute Vitality or
Vital Force, and are hence taken as the Cause of vital phenomena.
The dynamical definition will express the connexus of Functions and
Faculties of the organism, which are the statical properties of
organized substance in action, under definite relations.
It is obvious that the term Life must vary with the varying
significates it condenses,--every variation in the complexity of the
organism will bring a corresponding fulness in the signification of
the term. The life of a plant is less significant than the life of
an animal; and the life of a mollusc less than that of a fish. But
not only is the term one of varying significance, it is always an
abstract term which drops out of sight particular concrete differences,
registering only the universal resemblances.
* * * * *
27. It would be a profitless labor to search out, and a wearisome
infliction to set down, the various definitions which have been
proposed and accepted; but certain characteristic examples may be
selected. All that I am acquainted with belong to two classes: 1°, the
_meta_-physiological hypothesis of an _extra_-organic agent, animating
lifeless matter by unknown powers; 2°, the physiological hypothesis
which seeks the cause of the phenomena (i. e. the conditions) _within_
the organism itself,--a group of conditions akin to those manifested
elsewhere, but differently combined. The first hypotheses are known
under the names of Animism and Vitalism,--more commonly the latter. The
second are known as Organicism and Materialism,--but the latter term
only applies to some of the definitions.
28. Under Vitalism are included all the hypotheses of a soul, a spirit,
an archæus, a vital principle, a vital force, a _nisus formativus_,
a plan or divine idea, which have from time to time represented the
metaphysical stage of Biology. The characteristic of that stage is
the personification of a mystery, accompanied by the persuasion that
to name a mystery is to explain it. In all sciences when processes
are imperfectly observed, the _theory_ of the processes (which is a
systematic survey of the available evidence marshalled in the order
of causal dependence) is supplemented by _hypothesis_, which fills up
with a guess the gap left by observation. The difference between the
metaphysical and the positive stages of a science lies in the kind of
guess thus introduced to supplement theory, and the degree of reliance
accorded to it. I have more than once insisted on the scientific
canon that “to be valid, an explanation must be expressed in terms of
phenomena already observed”; now it is quite clear that most of the
extra-organic hypotheses do not fulfil this condition; no one having
ever _observed_ a spirit, an archæus, or a vital principle; but only
_imagined_ these agents to explain the facts observed. As an example of
the difference, and a proof that the value of an hypothesis does not
rest on the facility with which it connects observations, and seems
to explain them, take the three hypotheses of animal spirits, nervous
fluid, and electricity, by which neural processes have been explained.
The animal spirits are imaginary; the nervous fluid is without a basis
in observation, no evidence of such a fluid having been detected;
but electricity (or, speaking rigorously, the movements classed as
electrical), although not proved to be _the_ agent in nerve-action,
is proved to exist in nerves as elsewhere, and its modes of operation
are verifiable. It, therefore, and it alone of the three hypotheses,
is in conformity with the scientific canon. It may not, on full
investigation, meet all requirements; it may be rejected as imperfect;
but it is the kind of guess which scientific theory demands.
The second difference noticeable between the metaphysical and the
positive stages is the degree of reliance accorded to hypothesis;
which is very much the same as that noticeable in the uncritical and
critical attitudes of untrained and trained intellects. The one accepts
a guess as if it were a proof; is fascinated by the facility of linking
together isolated observations, and, relying on the guess as truth,
proceeds to deduce conclusions from it; the other accepts a guess as
an aid in research, trying by its aid to come upon some observation
which will reveal the hidden process; but careful never to allow the
guess to _supersede observation_, or to form a basis of deductions not
immediately verified.
29. A glance at the metaphysiological definitions will detect both the
kind of guess and the kind of reliance which prevailed. The mystery
was not simply recognized, it was personified as an entity: Will and
Intelligence were liberally accorded to it, for it was supposed to
shape matter, and direct force into predestined paths by prescience of
a distant end. The observed facts of the egg passing through successive
changes into a complex organism were so marvellous, so unlike any
facts observable in the inorganic world, that they seemed to demand a
cause drawn from higher sources. The mystery of life obtruded itself
at every turn. It was named, and men fancied it explained. But in
truth no mystery is got rid of by explanation, however valid; it is
only shifted farther back. Explanation is the resolution of a complex
phenomenon into its conditions of existence--the product is reduced to
its factors; the explanation is final when this resolution has been
so complete that a reconstruction of the product is possible from
the factors. The vast majority of explanations--especially in the
organic region--are no more than what mathematicians call “a first
approximation.” It is through successive approximations that science
advances; but even when the final stage is reached a mystery remains.
We may know that certain elements combine in certain proportions
to produce certain substances; but why they produce these, and not
different substances, is no clearer than why muscles contract or
organisms die. This Why is, however, an idle question. That alone which
truly concerns us is the How, and not the Why.
30. Biology is still a long way off the How. But it can boast of
many approximations; and its theories are to be tested by the degree
of approximation they effect. In this light the physiological,
_intra_-organic, hypotheses manifestly have the advantage. Many of them
are indeed very unacceptable; they are guided by a mistaken conception
of the truths reached by Analysis. For when men first began to discard
the extra-organic hypotheses, and to look into the organism itself,
they were so much impressed by the mechanical facts observed, that they
endeavored to reduce all the phenomena to Mechanics. The circulation
became simply a question of hydraulics. Digestion was explained as
trituration. The chemists then appeared, and their shibboleths were
“affinities” and “oxidations.” With Bichat arose the anatomical school,
which decomposing the organism into organs, the organs into tissues,
and these tissues into their elements, sought the analytical conditions
of existence of the organism in the properties of these tissues, and
the functions of these organs. The extra-organic agent was thus finally
shown to be not only a fiction, but a needless fiction.
Every student of the history of the science will note how from the very
necessities of the case the metaphysiologists, without relinquishing
their Vital Principle, have been led more and more to enter on the
track of the physiologists, pursuing their researches more and more
into the processes going on in the organism, and assigning more and
more causal efficiency to these, with a corresponding restriction
of the province of their extra-organic cause. Hence in the ranks of
the vitalists have been found some of the very best observers and
theorists; but they were such in despite of, and not in consequence
of, their hypothesis, which was only invoked by them when evidence
was at fault. Nor, unscientific as vitalism is, can we deny that it
has been so far serviceable to the science, that it has corrected the
materialist error of endeavoring to explain organic phenomena by
physico-chemical laws; and has persistently kept in view the radical
difference between organic and inorganic.
31. These remarks may justify a selection of definitions, classified
under the two heads. The selection is fitly opened by the Aristotelian
definition which prevailed for centuries.
Aristotle distinguishes Life, which he says means “the faculties of
self-nourishment, self-development, and self-decay,” from the Vital
Principle. Every natural body manifesting life may be regarded as an
essential existence (οὐσία); but _then it is an existence only as a
synthesis_ (ὡς συθέτη); and since an organism is such a synthesis,
being possessed of Life, it cannot be the Vital Principle (ψυχή).
Therefore it follows that the Vital Principle must be an essence, as
being the Form of a natural body holding life in _potentiality_. The
Vital Principle is the primary reality of an organism. “It is therefore
as idle to ask whether the Vital Principle and Organism are one, as
whether the wax and the impress on it are one.... Thus if an eye
were an animal, Vision would be its Vital Principle: for Vision is,
abstractedly considered, the essence of the eye; but the eye is the
body of Vision, and if Vision be wanting, then, save in name, it is no
longer an eye.”
Apart from certain metaphysical implications, inevitable at that
period, there is profound insight in this passage. His adversary
Telesio quite misconceives the meaning here assigned to the Vital
Principle.[8]
32. Let us pass over all the intermediate forms of the hypothesis, and
descend to Kant, who defines Life “an internal principle of action”
(this does not distinguish it from fermentation); an organism he says
is “that in which every part is at once means and end.” “Each part
of the living body has its cause of existence in the whole organism;
whereas in non-living bodies each part has its cause in itself.”
Johannes Müller adopts a similar view: “The harmonious action of the
essential parts of the individual subsist only by the influence of a
force, the operation of which is extended to all parts of the body,
and does not depend on any single parts; this _force must exist before
the parts_, which are in fact formed by it during the development of
the embryo.... The vital force inherent in them generates from the
organic matter the essential organs which constitute the whole being.
This _rational creative force_ is exerted in every animal strictly in
accordance with what the nature of each requires.”
33. This is decidedly inferior to Aristotle, who did not confound
the vegetative with the rational principle. It rests on the old
metaphysical error of a _vis medicatrix_, an error which cannot
sustain itself against the striking facts which constantly point to
a _vis destructrix_, a destructive tendency quite as inexorable as
the curative tendency. And the experimental biologist soon becomes
impressed with the fact that the tissues have indeed a _selective_
action, by which from out the nutrient material only these substances
are assimilated which will enter into combination with them; but this
selective action is fatal, no less than reparative: substances which
poison the tissue are taken up as readily as those which nourish
it. The idea of prescience, therefore, cannot be sustained; it is
indeed seldom met with now in the writings of any but the Montpellier
school, who continue the traditions of Stahl’s teaching. It has been
so long exploded elsewhere that one is surprised to find an English
physiologist clinging to a modification of it--I mean Dr. Lionel Beale,
who repeatedly insists on Life as “a peculiar Force, _temporarily
associated_ with matter,” a “power capable of controlling and directing
both matter and force,” an “_undiscovered_ form of force _having no
connection with primary energy or motion_.” “The higher phenomena of
the nervous system are probably due primarily to the movements of the
germinal matter due to vital power, which vital power of this the
highest form of germinal matter is in fact the living _I_.”
34. Apart from the primary objection to all these definitions,
namely, that they seek to express organic phenomena in terms of an
extra-organic principle, to formulate the facts _observed_ in terms
of a cause _inferred_, there is the fatal objection that they speak
confidently on what is avowedly unknown. If the force be, as Dr. Beale
says, “undiscovered,” on what grounds can he assert that it has _no_
connection with the forces which are known? All that the observed facts
warrant is the assertion that organic phenomena are special (which
no one denies), and must therefore depend on special combinations of
matter and force. But on this ground we might assume a crystallizing
Force, and a coagulating Force, having no connection with the molecular
forces manifested elsewhere: these also are special phenomena, not to
be confounded with each other.
35. Schelling defines Life as “a principle of individuation” and a
“cycle of successive changes determined and fixed by this internal
principle.” Which is so vague that it may be applied in very different
senses. Bichat’s celebrated definition (which is only a paraphrase of
a sentence in Stahl), “the sum of the functions which resist Death,”
although an endeavor to express the facts from the Intra-organic point
of view, is not only vague, but misrepresents one of the cardinal
conditions, by treating the External Medium as antagonistic to Life,
whereas Life is only possible in the relation to a Medium.
36. Were it not so vague, the definition proposed by Dugès and Béclard
would be unexceptionable: the former says it is “the special activity
of organized beings”; the latter, “the sum of the phenomena proper to
organized bodies.” When supplemented by a description of organized
bodies, these formulæ are compendious and exact. The same remark
applies to the definition of Lamarck: “that state of things which
permits organic movements; and these movements, which constitute active
life, result from a stimulus which excites them.”
37. De Blainville, and after him Comte and Charles Robin, define
it thus: “Life is the twofold internal movement of composition and
decomposition at once general and continuous.” This, excellent as
regards what is called vegetal life, is very properly objected to by
Mr. Herbert Spencer in that it excludes those nervous and muscular
functions which are the most conspicuous and distinctive of vital
phenomena. The same objection must be urged against Professor Owen’s
definition: “Life is a centre of intussusceptive assimilative force
capable of reproduction by spontaneous fission.”
38. In 1853, after reviewing the various attempts to express in a
sentence what a volume could only approximately expound, I proposed the
following: “Life is a series of definite and successive changes, both
of structure and composition, which take place within an individual
without destroying its identity.” This has been criticised by Mr.
Herbert Spencer and by Dr. Lionel Beale, and if I had not withdrawn
it before their criticisms appeared, I should certainly have modified
and enlarged it afterwards. I mention it, however, because it is an
approach to a more satisfactory formula in so far as it specifies two
cardinal characteristics distinguishing organisms from all anorganisms,
namely, the incessant evolution through definite stages, and the
preservation of specific integrity throughout the changes; not only
the organism as a whole is preserved amidst incessant molecular
change, but each tissue lives only so long as the reciprocal molecular
composition and decomposition persist. On both of these points I shall
have to speak hereafter. The definition, however, is not only defective
in its restriction to the molecular changes of Nutrition, taking no
account of the Properties and Functions of the organism; but defective
also in giving no expression to equally important relations of the
organism to the medium.
39. This last point is distinctly expressed in Mr. Spencer’s
definition: “Life is the continuous adjustment of internal relations
to external relations.” Considered as a formula of the most general
significance, embracing therefore what is common to all orders of vital
phenomena, this is the best yet proposed.[9] If I propose another it
will not be to displace but to run alongside with Mr. Spencer’s; and
this only for more ready convenience. Before doing so I must say a few
words by way of clearing the ground.
40. What does the term Life stand for? What are the concrete
significates of this abstract symbol? As before stated, it is sometimes
a compendious shorthand for the special phenomena distinguishing living
from non-living bodies; and sometimes it expresses not these observed
phenomena, but their conditions of existence, which are by one school
personified in an abstract and extra-organic cause. Thus the life of
an animal, a man, or a nation, means--1°, the special manifestations
of these organisms, and groups of organisms; or 2°, the causes which
produce these manifestations. We are often misunderstood by others, and
sometimes vague to ourselves, when we do not bear these two different
meanings in view. It was probably some sense of this which made
Aristotle distinguish Vitality from Life, as that of the one uniform
cause separated from its multiple effects; it was certainly the motive
of Fletcher, who thus expressly limits the meanings: “_Vitality_ or
_Irritability_, the property which characterizes organized beings
of being acted on by certain powers otherwise than either strictly
mechanically or strictly chemically; _Life_, the sum of the actions
of organized beings resulting directly from their vitality so acted
on.”[10]
Vitality and Life being thus discriminated as the statical and
the dynamical aspects of the organism, we find in relation to the
former two radically opposed conceptions: the metaphysiological or
extra-organic, and the physiological or intra-organic. The first
conceives Vitality to be a Vital Principle, or extra-organic agent,
sometimes a soul, spirit, archæus, idea, and sometimes a force, which
easily becomes translated into a property.
The conception of an entity must be rejected, because it is
metempirical and unverifiable, § 34. The conception of a force must
be rejected, because it is irreconcilable with any definite idea we
have of force. What the term Force signifies in Physics and Chemistry,
namely, mass animated by velocity, or _directed pressure_, which is
the activity of the agent,--is precisely that which these vitalists
pertinaciously exclude. They assume a force which has nothing in
common with mass and velocity; which is _not a resultant, but a
principle_; which instead of being a _directed quantity_, is itself
autonomous and _directive_, shaping matter into organization, and
endowing it with powers not assignable to matter. If this vital force
has any mass at its back, it is a spiritual mass; if it is directed,
the direction issues from a “Mind somewhere.” Now this conception is
purely metempirical. Not only is it inexact to speak of Vitality as
a force, it is almost equally inexact to speak of it as a property;
since it is a term which includes a variety of properties; and when
Fletcher assigns the synonym of Irritability, this at once reveals the
inexactness; for beside this property, we must place Assimilation,
Evolution, Disintegration, Reproduction, Contractility, and
Sensibility,--all characteristic properties included in Vitality.
41. Having thus rejected the conceptions of entity, force, and
property, we are left in presence of--1°, the organic conditions as the
elements, and 2°, of their synthesis (in the state called organization)
as the personified principle. Vital forces, or the vital force, if
we adopt the term for brevity’s sake, is a _symbol of the conditions
of existence of organized matter_; and since organisms are specially
distinguishable from anorganisms by this speciality of their synthesis,
and not by any difference in the nature of the elements combined, this
state of organization is the “force” or “principle” of which we are in
quest. To determine what Life means, we must observe and classify the
phenomena presented by living beings. To determine what Vitality--or
organization--means, we must observe and classify the processes which
go on in organized substances. These will occupy us in the succeeding
chapters; here I may so far anticipate as to propose the following
definitions:--
42. Life is the functional activity of an organism in relation to
its medium, as a synthesis of three terms: Structure, Aliment, and
Instrument; it is the sum of functions which are the resultants of
Vitality; Vitality being the sum of the properties of matter in the
state of organization.
43. Vital phenomena are the phenomena manifested _in_ organisms when
external agencies disturb their molecular equilibrium; and _by_
organisms when they react on external objects. Thus everything done in
an organism, or by an organism, is a vital act, although physical and
chemical agencies may form essential components of the act. If I shrink
when struck, or if I whip a horse, the blow is in each case physical,
but the shrinking and the striking are vital.
Every part of a living organism is therefore vital, as _pertaining_
to Life; but no part has this Life when isolated; for Life is the
synthesis of all the parts: a federation of the organs when the
organism is complex, a federation of the organic substances when the
organism is a simple cell.
44. All definitions, although didactically placed at the introduction
of a treatise, are properly the final expression of the facts which
the treatise has established, and they cannot therefore be fully
apprehended until the mind is familiarized with the details they
express. Much, therefore, which to the reader may seem unintelligible
or questionable in the foregoing definition, must be allowed to pass
until he has gone through the chapters which follow.
CHAPTER III.
ORGANISM, ORGANIZATION, AND ORGANIC SUBSTANCE.
45. There is a marked difference between organ_ic_ and organ_ised_
substances. The organic are non-living, though capable of living
when incorporated in organized tissue (albumen is such a substance);
or they may be incapable of living because they have lived, and are
products of waste, e. g. urea. The organized substance is a specific
combination of organic substances of various kinds, a combination
which is organization. Any organized substance is therefore either an
independent organism, or part of a more complex organism. Protoplasm,
either as a separate organism or as a constituent of a tissue, is
organized substance.
Organic substances are numerous and specific. They are various
combinations of proximate principles familiar to the chemist, which may
conveniently be ranged under three classes: The first class of organic
substances comprises those composed of principles having what is called
a mineral origin; these generally quit the organism unchanged as they
entered it. The second class comprises those which are crystallizable,
and are formed _in_ the organism, and generally quit it in this state
as excretions. The third class comprises the colloids, i. e. substances
which are coagulable and not crystallizable, and are formed in and
decomposed in the organism, thus furnishing the principles of the
second class. All the principles are in a state of solution. Water is
the chief vehicle of the materials which enter and the materials which
quit the organism; and bodies in solution are solvents of others, so
that the water thus acquires new solvent properties.
45_a_. Two points must be noted respecting organic substances: they are
mostly combinations of _higher multiples_ of the elements; and their
combinations are not _definite_ in quantity. Albumen, for example,
has (according to one of the many formulas which have been given) an
elementary composition of 216 atoms of Carbon, 169 of Hydrogen, 27 of
Nitrogen, 3 of Sulphur, and 68 of Oxygen; whereas in its final state,
in which it quits the organism as Urea, it is composed of 2 atoms
of Carbon, 4 of Hydrogen, 2 of Nitrogen, and 2 of Oxygen, all the
Sulphur having disappeared in other combinations. In like manner in
the organism Stearin falls from C_{114}, H_{110}, O_{12}, to Oxalic
Acid, which is C_{4}, H_{2}, O_{8}. It is obvious that the necessary
modifiability of organic substance is due to this multiplicity of its
elementary parts and the variety of its molecular structure.
45_b_. Nor is the indefiniteness of the quantitative composition less
important, though seldom adequately appreciated, or even suspected.
Robin and Verdeil[11] are the only writers I can remember who have
distinctly brought the fact into prominence. That all inorganic
substances are definite in composition, every one knows. Quicklime,
for example, may be got from marble, limestone, oyster-shells, or
chalk; but however produced, it always contains exactly 250 ounces
of calcium to 100 ounces of oxygen; just as water is always OH_{2}.
Not so the pre-eminently vital substances, those which are coagulable
and not crystallizable: no precise formula will express one of these;
for the same specific substance is found to vary from time to time,
and elementary analyses do not give uniform results. Thus, if after
causing an acid to combine with one of these substances, we remove
the acid, we are not certain of finding the substance as it was
before--as we are, for example, after urea is combined with nitric
acid and then decomposed. The same want of definiteness is of course
even more apparent in the _combinations_ of these proximate principles
into organized substance. Protoplasm differs greatly in different
places. Epithelial cells differ. Muscular and nervous fibres are never
absolutely the same in different regions. A striped and unstriped
muscular fibre, the muscular fibre of a sphincter or of a limb, a
nerve-fibre in a centre, in a trunk, or in a gland, will present
variations of composition. The elastic fibres of the ligaments are
larger in the horse than in man; and in other animals they are smaller.
These differences are sometimes due to the constituents, and sometimes
to the arrangement of the constituents; the conversion of Albumen into
Fibrine without elementary loss or addition, is a good example of the
latter. That the tissues of one man are not absolutely the same as
the tissues of another, in the sense in which it is true to say that
the chalk of one hill is the same as that of another, or as gold in
Australia is the same as gold in Mexico, is apparent in their very
different reactions under similar external conditions: the substance
which poisons the one leaves the other unaffected. The man who has once
had the small-pox, or scarlet fever, is never the same afterwards,
since his organism has now become insusceptible of these poisons. And
Sir James Paget has called attention to the striking fact revealed in
disease, namely, that in the same tissue--say the bone or the skin--a
morbid substance fastens only on certain small portions leaving all
the rest unaltered, but fastens on exactly corresponding spots of the
opposite sides of the body; so that on both arms, or both legs, only
the corresponding bits of tissue will be diseased. “Manifestly when
two substances display different relations to a third their composition
cannot be identical; so that though we may speak of all bone or
of all skin as if it were all alike, yet there are differences of
intimate composition. No power of artificial chemistry can detect the
difference; but a morbid material can.”[12] It is to this variability
of composition that we must refer individual peculiarities, and those
striking forms of variety known as idiosyncrasies, which cause some
organisms to be affected by what seem inexplicable influences--physical
and moral.
In spite of all these variations, however, there are certain specific
resemblances dependent of course on similarity of composition and
structure, so that the muscle of a crustacean is classed beside the
muscle of a vertebrate, although the elementary analysis of the two
yields different results. Nerve-tissue, according to my experience,
is the most variable of all, except the blood; variable not only from
individual to individual, and from genus to genus, but even in the same
individual it never contains the same quantities of water, phosphates,
etc. Hence it is that different nerves manifest different degrees of
excitability, and the same nerve differs at different times. Thus the
fifth pair, in a poisoned animal, retains its excitability long after
the others are paralyzed; and the patient under chloroform feels a
prick on the brow or at the temples, when insensible at any other spot.
The pneumogastric which is excitable during digestion is--in dogs at
least--inexcitable when the animal is fasting.
46. The organic substances are what analysis discovers in organized
substances, but none of them, not even the highest, is living, except
as organized. Albumen alone, or Stearin alone, is as incapable of
Vitality, as Plumbago, or Soda; but all organic substances are
capable of playing a part in vital actions; and this part is the
more important in proportion to their greater molecular variety.
Organization is a special synthesis of substances belonging to all
three classes; and the organized substance, thus formed, alone merits
the epithet living. We see how organized substances, being constituted
by principles derived from the inorganic world, and principles derived
from the organic world, have at once a dependence on the external
Medium, and an independence of it, which is peculiar to living beings.
An analogous dependence and independence is noticeable with respect to
the parts; and this is a character not found in inorganic compounds.
The organism, even in its simplest forms, is a structure of different
substances, each of which is complex. While one part of a crystal is
atomically and morphologically identical with every other, and is the
whole crystal “writ small,” one part of an organism is unlike another,
and _no part_ is like the whole. Hence the dependence of one organ and
one tissue on another, and each on all. Yet, while every part is, so to
speak, a condition of existence of every other, and the unity of the
organism is but the expression of this solidarity,--wherever organized
substance has been differentiated into morphological elements (cells,
etc.), each of these has its own course of evolution independently of
the others,--is born, nourished, developed, and dies.
47. The interdependence of nerve and muscle is seen in this, that the
more the muscle is excited the feebler its contractions become; this
decrease in contractility is compensated by an increased excitability
in its nerve; so that while the muscle demands a more powerful
stimulus, the nerve acquires a more energetic activity. Ranke’s curious
and careful experiments seem to prove that this depends on the wearied
muscle absorbing more water, owing to the acids developed by its
activity, and on the nerve losing this water--a nerve being always
more irritable when its quantity of water diminishes.
48. Herein we see illustrated the great law of organized activity,
that it is a simultaneity of opposite tendencies, as organized matter
is a synthesis of compositions and decompositions, always tending
towards equilibrium and disturbance, storing up energy and liberating
it. Unlike what is observed in unorganized matter, the conditions of
waste bring with them conditions of repair, and thus--within certain
limits--every loss in one direction is compensated by gain in another.
There is a greater flow of nutrient material, or, more properly
speaking, a greater assimilation of it by the tissue, where there has
been made a greater opening for it by previous disintegration. The
alkaline state of the nutrient material, and the acid state of the
material that has been used,--the alkaline state which characterizes
repose and assimilation, and the acid state which characterizes
activity and deassimilation, are but cases of this general law; on the
synthesis of these opposite tendencies depends the restless change,
together with the continued specific integrity, of organized matter.
49. The state of organization may therefore be defined as the
_molecular union of the proximate principles of the three classes
in reciprocal dissolution_. An organism is formed of matter thus
organized, which exists in two states--the _amorphous_ and the
_figured_. The amorphous substances are liquid, semi-liquid, and solid;
the figured are the cells, fibres, and tubes, called “anatomical
elements.” For these I prefer the term suggested, I believe, by Milne
Edwards, namely, _organites_, because they are the individual elements
which mainly constitute the organs, and are indeed by many biologists
considered as elementary organisms. These organites, which go to form
the tissues, and by the tissues the organs, have their specific form,
volume, structure, and chemical reactions. They exist in textures
or tissues, or separately (e. g. blood corpuscles), and are in many
respects like the simplest organisms known, such as Monads, Vibrios,
Amœbæ, etc.
50. The simplest form of life is not--as commonly stated--a cell, but
a microscopic lump of jelly-like substance, or protoplasm, which has
been named _sarcode_ by Dujardin, _cytode_ by Haeckel, and _germinal
matter_ by Lionel Beale. This protoplasm, although entirely destitute
of texture, and consequently destitute of organs, is nevertheless
considered to be living, because it manifests the cardinal phenomena
of Life: Assimilation, Evolution, Reproduction, Mobility, and
Decay. Examples of this simplest organism are Monads, Protamœbæ,
and Polythalamia.[13] Few things are more surprising than the vital
activity of these organites, which puzzle naturalists as to whether
they should be called plants or animals. All microscopists are familiar
with the spectacle of a formless lump of albuminous matter (a Rhizopod)
putting forth a process of its body as a temporary arm or leg, or else
slowly wrapping itself round a microscopic plant, or morsel of animal
substance, thus converting its whole body into a mouth and a stomach;
but these phenomena are surpassed by those described by Cienkowski,[14]
who narrates how one Monad fastens on to a plant and sucks the
chlorophyll first from one cell and then from another; another Monad,
unable to make a hole in the cell-wall, thrusts long processes of its
body into the opening already made, and drags out the remains of the
chlorophyll left there by its predecessor; while a third Monad leads a
predatory life, falling upon other Monads that have filled themselves
with food. Here, as he says, we stand on the threshold of that dark
region where Animal Will begins; and yet there is here only the
simplest form of organization.[15]
51. Now let our glance pass on to the second stage--the Cell. Here we
have a recognized differentiation in the appearance of a nucleus amid
the protoplasm. The nucleus is chemically different from the substance
which surrounds it; and although perhaps exaggerated importance has
been attributed to this nucleus, and mysterious powers have been
ascribed to it, yet as an essential constituent of the cell it commands
attention. Indeed, according to the most recent investigations, the
definition of a cell is “a nucleus with surrounding protoplasm.” The
cell-wall, or delicate investing membrane--that which makes the cell a
closed sac--is no longer to be regarded as a necessary constituent, but
only as an accessory.[16]
52. The cell may be either an organism or an organite. It may lead an
isolated life as plant or animal, or it may be united with others and
lead a more or less corporate existence; but always, even as an element
of a higher organism, it preserves its own individuality. At first we
see that the corporate union is very slight, merely the contact of one
cell with another of its own kind, as in the filament of a Conferva.
Rising higher, we see the cell united with others different from
it; plants and animals appear, having structures composed of masses
of various cells. Rising still higher, we see animal forms of which
the web is woven out of myriads upon myriads of cells, with various
cell-products, processes, fibres, tubes.
ORGANISM AND MEDIUM.
53. But we have only one half of the great problem of life, when we
have the organism; and it is to this half that the chief researches
have been devoted, the other falling into neglect. What is that
other? The Medium in which the organism lives. Every individual
object, organic or inorganic, is the product of two factors:--first,
the relation of its constituent molecules to each other; secondly,
the relation of its substance to all surrounding objects. Its
properties, as an object or an organism, are the results of its
constituent molecules, and of its relation to external conditions.
Organisms are the results of a peculiar group of forces, exhibiting
a peculiar group of phenomena. Viewing these in the abstract, we
may say that there are three regulative laws of life:--(1) The _Lex
Formationis_--the so-called _nisus formativus_, or “organizing force”;
(2) the _Lex Adaptationis_, or adaptive tendency; (3) the _Lex
Hereditatis_, or tendency to reproduce both the original form and its
acquired modifications. We have always to consider the organizing
force in relation to all surrounding forces--a relation succinctly
expressed in the word Adaptation. Just as water is water only under a
certain relation of its constituent molecules to the temperature and
atmospheric pressure--just as it passes into other forms (ice or steam)
in adapting itself to other conditions; so, likewise, the organism only
preserves its individuality by the adjustment of its forces with the
forces which environ it.
54. This relation of Organism and Medium, the most fundamental of
biological data, has had a peculiar fortune: never wholly unrecognized,
for it obtrudes itself incessantly in the facts of daily experience,
it was very late in gaining recognition as a principle of supreme
importance; and is even now often so imperfectly apprehended that one
school of philosophers indignantly rejects the idea of the Organism and
Medium being the two factors of which Life is the product. Not only
is there a school of vitalists maintaining the doctrine of Life as an
entity independent both of Organism and Medium, and using these as its
instruments; but there is also a majority among other biologists, who
betray by their arguments that they fail to keep steadily before them
the fundamental nature of the relation. Something of this is doubtless
due to the imperfect conception they have formed of what constitutes
the Medium; instead of recognizing in it the sum of external conditions
affecting the organism--i. e. the sum of the relations which the
organism maintains with external agencies,--they restrict, or enlarge
it, so as to misapprehend its significance--restrict it to only a few
of the conditions, such as climate, soil, temperature, etc., or enlarge
it to embrace a vast array of conditions which stand in no directly
appreciable relation to the organism. Every one understands that an
organism is dependent on proper food, on oxygen, etc., and will perish
if these are withheld, or be affected by every variation in such
conditions. Every one understands that an animal which can devour or be
devoured by another, will flourish or perish according to the presence
of its prey or its enemy. But it is often forgotten that among external
existences, all those which stand in no appreciable relation to the
organism are not properly to be included in its Medium. In consequence
of this oversight we frequently hear it urged as an objection to the
Evolution Hypothesis, that manifold organisms exist under the _same_
external conditions, and that organisms persist unchanged amid a
great variety of conditions. The objection is beside the question. In
the general sum of external forces there are certain items which are
nearly related to particular organisms, and constitute their Medium;
those items which are so distantly related to these organisms as to
cause no reactions in them, are, for them, as if non-existent.[17] Of
the manifold vibrations which the ether is supposed to be incessantly
undergoing, only certain vibrations affect the eye as light; these
constitute the Medium of Sight; the others are as if they were not.
Only certain vibrations of the air affect the ear as Sound; to all
other vibrations we are deaf; though ears of finer sensibility may
detect them and be deaf to those which affect us.
55. “The external conditions of existence” is therefore the correct
definition of the Medium. An animal may be surrounded with various
foods and poisons, but if its organism is not directly affected by them
they cannot be food or poison to it. An animal may be surrounded with
carnivorous rivals, but if it is not adapted to serve them as food, or
is too powerful to be attacked by them, they only indirectly enter into
its Medium, by eating the food it would eat. The analogy is similar
with anorganisms and their relation to their media. Every physical or
chemical phenomenon depends on the concurrence of definite conditions:
namely, the substance which manifests the change, and the medium in
which the change is manifested. Alter the medium, solid, liquid, or
gaseous, change its thermal or electrical state, and the phenomenon is
altered. But although similar alterations in the medium notoriously
influence the organism, yet, because a great many variations in
external conditions are unaccompanied by appreciable changes in the
organism, there are biologists who regard this as a proof of Life being
independent of physical and chemical laws; an error arising from their
not recognizing the precise nature of organic conditions.
56. To give greater precision to the conception of a Medium it will
be desirable to adopt the distinction much insisted on by Claude
Bernard, namely, 1°, an External or Cosmical Medium, embracing the
whole of the circumstances outside the organism, capable of directly
affecting it, and 2°, an Internal or Physiological Medium, embracing
the conditions inside the organism, and in direct relation with
it--that is to say, the plasma in which its tissues are bathed, by
which they are nourished. To these add its temperature and electrical
conditions. Bernard only includes the nutritive fluid; but inasmuch as
each organism possesses a temperature and electrical state of its own,
and these are only indirectly dependent on the external temperature
and electricity, and as it is with these internal conditions that
the organism is in direct relation, I include them with the plasma
among the constituents of the Physiological Medium. Any change in the
External Medium, whether of temperature or electricity, of food or
light, which does not disturb the Internal Medium, will of course leave
the organism undisturbed; and for the most part all the changes in
the External Medium which do affect the organism, affect it by first
changing the Internal Medium. External heat or cold raises or depresses
the internal temperature _indirectly_ by affecting the organic
processes on which the internal temperature depends. We see here the
rationale of acclimatization. Unless the organism can adapt itself to
the new External Medium by the readjustment of its Internal Medium, it
perishes.
57. We are now enabled to furnish an answer to the very common
objection respecting the apparent absence of any direct influence of
external conditions. Let the objection first be stated in the words
of a celebrated naturalist, Agassiz: “It is a fact which seems to be
entirely overlooked by those who assume an extensive influence of
physical causes upon the very existence of organized beings, that the
most diversified types of animals and plants are everywhere found under
identical circumstances. The smallest sheet of fresh water, every
point of the sea-shore, every acre of dry land, teems with a variety
of animals and plants. The narrower the boundaries which are assigned
as the primitive home of all these beings, the more uniform must be
the conditions under which they must be assumed to have originated; so
uniform indeed that in the end the inference would be that the same
physical causes can produce the most diversified effects.”
Obviously there is a complete misstatement of the argument here; and
the excess of the misstatement appears in the following passage: “The
action of physical agents upon organized beings presupposes the very
existence of those beings.” Who ever doubted it? “The simple fact that
there has been a period in the history of our earth when none of these
organized beings as yet existed, and when, nevertheless, the material
constitution of our globe and the physical forces acting upon it were
essentially the same as they are now, shows that these influences are
insufficient to call into existence any living being.”[18] Although
most readers will demur to the statement that because the material
constitution of our globe was “essentially the same” before and after
animal life appeared, therefore there could have been no special
conditions determining the appearance of Life, the hypothesis of
Evolution entirely rejects the notion of organic forms having been
diversified by diversities in the few physical conditions commonly
understood as representing the Medium. Mr. Darwin has the incomparable
merit of having enlarged our conception of the conditions of existence
so as to embrace _all_ the factors which conduce to the result. In
his luminous principle of the Struggle for Existence, and the Natural
Selection which such a struggle determines, we have the key to most of
the problems presented by the diversities of organisms; and the Law of
Adaptation, rightly conceived, furnishes the key to all organic change.
58. In consequence of the defective precision with which the phrase
“Medium,” or its usual equivalent “physical conditions,” is employed,
several biological errors pass undetected. Haeckel[19] calls attention
to the common mistake of supposing the organism to be passive under the
influence of external conditions, whereas every action, be it of light
or heat, of water or food, necessarily calls forth a corresponding
reaction, which manifests itself in a modification of the nutritive
process. He points out the obverse of this error in the current notion
that Habit is solely due to the spontaneous action of the organism,
in opposition to the influence of external agency,--as if every
action were not the response to a stimulus. Corresponding with the
fluctuations in the Medium there must necessarily be fluctuations of
Adaptation, and I think we may safely assume that it is only when these
fluctuations cease that the Adaptation becomes Habit. This is the
interpretation of the phrase “Habit is _second_ Nature,” and is very
different from the common interpretation which attributes it to the use
or disuse of organs; as if use or disuse were a spontaneous uncaused
activity.
59. The organism, simple or complex, is, we have already seen, built
up from materials originally derived from the External Medium, but
proximately from the Internal Medium. This statement, however, requires
some qualification, especially in view of the hypothesis that organized
substance was originally created such as we now find it, and not
evolved from inorganic materials. Whether this hypothesis be adopted,
or rejected, we have the fact that the immense majority of organisms
_now_ existing--if not all--are products of pre-existing organisms;
and therefore organized matter is now mainly, if not solely, formed by
organized matter.
We take, therefore, as our point of departure, the protoplasm; this
is the first of the three terms of the vital synthesis: Structure,
Aliment, and Instrument. The evolution of this is proximately
dependent on the _pabulum_ afforded it in the Internal Medium, which
is the true nutrient material, and to which what is usually called
_food_ stands in an external relation: for between the reception of
food and its assimilation by the organite, there is an indispensable
intermediary stage, through which matter passes from the unorganized
to the organized state. This intermediate is now recognized in plants
as in animals. The old belief that plants were nourished _directly_
from the soil and atmosphere can no longer be sustained. The process
of Nutrition is alike in both: in both the materials drawn from the
External Medium are formed into proximate principles and organic
substances. It is daily becoming more and more probable that the
inorganic materials, water and oxygen, so freely entering into the
organism, never pass directly from the External Medium to the tissues,
but have to pass through the Internal Medium where they are changed,
so that the water is no longer free, but exists in a fixed state
which has no analogue out of the living substance. Only a part of
the water can be pressed out mechanically; the rest--that which is
already incorporated with the other elements--can only be got rid
of in a vacuum and at a high temperature. Oxygen, also, comports
itself differently in the tissue; as is proved by the fact that its
physiological absorption is markedly different from any chemical
oxidation in a dead or decomposing tissue.[20] Be this as it may, we
know that organic substances have to be unbuilt and rebuilt in the
organism; that the albumen of our food never passes directly into
the albumen of our tissues; any more than the milk drunk by a nursing
mother will pass into her breasts, and increase her supply, except by
nourishing her.
60. In the First Series of these Problems the term Bioplasm was
employed to designate this organized part of the Internal Medium. I
was led to adopt it as a corresponding term to that of Psychoplasm,
by which I wished to designate the _sentient_ material of the
psychological medium. There can be little doubt that the term Bioplasm
was an unconscious reproduction of the title of Dr. Beale’s work,
which I must have seen advertised. I withdraw it now that I have read
Dr. Beale’s work, and see that the signification he attaches to the
term is almost identical with Protoplasm. In lieu thereof, the term
Plasmode (from _plasma_, anything formed, and _odos_, a pathway) may
be substituted: it represents the _nutrient_ material on its way to
form Protoplasm, which is _formative_ material; while the materials
_formed_ may be termed Organites and Products: the organite being
the cell or cell-derivative (fibre, tube); the products being the
gaseous liquid and solid derivatives of vital processes, which are
_secretions_ when they form intercellular substance or return into the
plasmode and re-enter the vital circle; _excretions_ when they are
rejected, as incapable of further assimilation. The liver-cell will
furnish an example of each kind of product. The bile, though containing
principles serviceable in the chemical transformations, is for the
most part excreted; but besides bile, the liver-cell produces starchy
and saccharine principles which are true secretions, and re-enter the
plasmode.
61. The organite is thus composed of sap, substance, and product;
the organism, of plasmode, tissue, and product. A glance at the
vegetable-cell shows it to be constituted by the primordial utricle,
or protoplasm, the outermost layer of which is condensed into a
membrane, or cell-wall, and the cavity thus enclosed is filled with
sap. The cell-wall grows as the protoplasm grows, and the protoplasm
draws its material from the plasmode. A glance at the blood, the great
reservoir of the river of life, shows us plasmode in the serum, and
organites in the corpuscles; the one distinguished by sodic salts,
the other by potassic salts. The plasmode, or serum, is in a constant
change of composition and decomposition, giving up to the various
tissue-organites and intercellular plasmodes the requisite materials,
and receiving from organites and plasmodes the products of their
changes. The serum is fed from the food _and_ the tissues; and it feeds
the several plasmodes which bathe the several tissues. Passing into the
capillaries, it becomes transformed as it passes through their walls
into the intercellular spaces, saturating the acid products of the
cell-activities with its alkalies, and furnishing the protoplasms with
their needed materials.
62. It will be understood that, although in appearance these stages
are sharply defined, in reality they are insensible. But from the
analytical point of view we may regard Nutrition as the office
of the plasmode, and Evolution as the office of the protoplasm.
Although evolution or genesis of form depends on assimilation, it is
not a necessary consequence: the plasmode or the protoplasm might
preserve such perfect equality in the waste and repair, such complete
equilibrium, as not to undergo any development. The ova, for example,
which exist in the ovaries at birth are not all subsequently developed;
and if with modern embryologists we conclude that there is no
replacement of these by proliferation we shall in them have examples of
organites remaining unchanged through a period of fifty years.[21] But
such an equilibrium is perhaps only possible in complete inactivity.
63. Again, although the office of the plasmode is primarily that of
forming protoplasm, I think there is evidence to suggest that it not
only does this, but that some of it is used in the direct development
of energy, especially heat and electricity. The various forms of starch
and sugar taken in with the food or formed in the liver, certainly do
not as such enter into protoplasm. The same with alcohol.
64. It is perhaps in forgetfulness of the artificial nature of
analytical distinctions that controversies rage respecting what are
called intercellular substances and cell-walls. Now that the wall
is no longer regarded as an essential constituent of the cell, but
as a secondary formation, two opinions are maintained: first, that
it is merely a concentration of the external layer of protoplasm;
secondly, that it is a product of secretion from the protoplasm.
Both positions may be correct. Certainly in some cases there is no
other appreciable difference between wall and protoplasm than that
of a greater consistence; whereas in many other cases there exists a
decided difference in their chemical reactions, showing a difference
of composition. Taking both orders of fact, we may conclude that the
cell-wall is sometimes part of the organite, and sometimes product: a
blood-cell and a cartilage-cell may be cited as examples of each. And
this argument applies to the intercellular substance also.
65. The terms plasmode and protoplasm are general, and include many
species. There are different plasmodes for the different tissues,
so that we find phosphates of soda in the blood-serum, phosphates
of potash in the nerve-plasma, phosphates of magnesia in the
muscle-plasma, and phosphates of lime in the bone-plasma; having
severally to form the specifically different protoplasms of these
tissues. Observe, moreover, the gradations of these in respect of their
physical state: the blood being the most liquid, the nerve a degree
more solid, the muscle still more solid, and the bone almost entirely
solid; and since solubility of material is a necessary condition of
the chemical changes, we can understand how the blood, the nerve, the
muscle, and the bone represent degrees of vital activity: the greater
the instability of organized substance, the more active its molecular
renovation. Many serious errors result from overlooking the specific
differences of protoplasms; among them may be mentioned that very
common one of asserting that the ovum of a man is not distinguishable
from the ovum of any other mammal, nor the ovum of a mammal from that
of a reptile; nay, we sometimes see it stated that the protoplasm from
which a mammal may be developed is the same as that which is the germ
of an oak. So long as this simply asserts that we have at present no
means of distinguishing them by any chemical or physical tests, there
can be no objection raised; but it is a serious misconception, which
any embryological investigation ought to rectify, to suppose that the
ovum is not specific from the first.
66. Between the organites and their plasmodes there is the necessary
relation, which corresponds with the relation between organisms and
their mediums. Once formed, the organites are arranged side by side,
or end on end, into textures or tissues, and these are grouped into
organs, every organ being constituted by a collection of tissues, as
every apparatus is by a collection of organs, and the organism by the
federation of all the parts. We have more than once insisted on the
necessity of synthetic interpretation to complete the indications of
analysis: which means that no account of vital phenomena is _real_
unless it takes in all the co-operant factors, both those of the
organism and the medium. Neglect of this canon vitiates Dr. Beale’s
otherwise remarkable labors.
THE HYPOTHESIS OF GERMINAL MATTER.
67. It may help to elucidate certain important points if I here examine
the hypothesis which Dr. Beale has worked out with such patient skill,
but with what seem to me such unphysiological results. He deserves, I
think, more applause than has been awarded to him, not only for the
admirable patience with which he has pursued the idea, but also for
the striking definiteness of the idea itself--always a great advantage
in an hypothesis, since it gives precision to research. If biologists
have paid but little attention to it, this is no doubt due to the
theoretical, still more than to the observational contradictions it
presents. Histologists dispute his facts, or his interpretations;
while other biologists do not see their way in the application of
his hypothesis. Respecting all disputed points of observation I
shall be silent, for I have myself made no systematic researches in
this direction, such as would entitle me to form an estimate of the
evidence. But my dissent from the hypothesis is founded on biological
principles so fundamental that I should be willing to take my stand
entirely on the facts he himself puts forward.[22]
68. The hypothesis is that nothing in the organism has any claim
to vitality except the minute masses of protoplasm (by him called
bioplasm), which in the egg represent, he thinks, about the
one-thousandth part of the whole mass, the rest being lifeless matter,
namely, pabulum, and formed material. This bioplasm is the _germinal
matter_ out of which, by a _process of dying_, arise the tissues and
humors constituting the _formed material_--these, with the pabulum
which feeds the germinal matter, being all dead material. The germinal
matter itself, though living, only lives because there is temporarily
associated with it that Vital Force of which we have already spoken (§
14). In virtue of this association, a particle of matter not exceeding
the one hundred-thousandth of an inch in diameter is said to be alive;
and, presumably, to contain within it all those manifold powers which
the term Life condenses. The pabulum brought under the influence of
this Vital Force is transformed into germinal matter which, escaping
from this mysterious influence, _dies into tissue_. Muscle-fibres and
nerve-fibres are thus not living parts, nor are their actions vital. So
that, to be consistent, we must not speak of the organism as living,
but as a dead structure _produced_ by the Vital Force, and _set in
action_ by the aid of scattered bits of germinal matter. He has not, I
think, stated whether each of these bioplasms has its own Vital Force,
so that the organism is the theatre of millions of Vital Forces; or
whether it is one Vital Force which animates the whole organic world of
plants and animals. But nothing can be less equivocal than his position
respecting the lifelessness of every part of the organism except the
germinal matter.
69. The germinal matter may be selected as the primary stage of the
formed material, the initial point of growth, and thus stand for the
pre-eminently distinctive centre of Nutrition; but were we to limit all
Nutrition to the germinal matter, as defined by Dr. Beale, and deny
the co-operation of all the formed material, we should still not be
justified in restricting Life to simple Nutrition. We cannot exclude
such phenomena as those of Sensation and Motion, nor can we assign
these to the germinal matter.[23] To suppose this, would be equivalent
to saying that the steam which issues from a teakettle is capable of
the actions of a locomotive engine. The steam from the kettle is like
the steam from the boiler, it has molecular energy, and by this will
co-operate in the production of mechanical work, if the mechanism be
adjusted to it. The molecular energy of the protoplasm in muscular
fibre may be indispensable to the movements of the muscles, but these,
and not the protoplasmic movements alone, are muscular contractions. An
hypothesis, therefore, which is obliged to declare that muscle-fibre
and nerve-fibre are not living, even when active in the organism,
seems to me defective at its base. If we view these apart from the
organism, they may, like all the other formed materials, be regarded
as dead; and no one doubts that epidermis, nail, horn, hair, and bone
are dead in this sense, that they cannot live independently, and do not
reproduce themselves. But so long as even these form constituents of
the living organism, they also are _living_ (§ 42).[24] It is only by a
misconception of the analytical artifice that so simple a truth could
have been missed.
70. But this misconception meets us at many a turn. The Vitalist
hypothesis of an extra-organic agent of course refuses to regard Life
as the expression of all the co-operant conditions; and even opponents
of that hypothesis often fall into the same error of principle, when
they attempt to explain Life by localizing it in the cells; which is
simply a morphological substitution for the once popular doctrine that
only the vascular parts were organized, and every part destitute of
blood-vessels was dead. This idea seemed supported by the facts of the
most highly vascular parts being the most vital, and of a parallelism
existing between the vital activity of those organs which when injected
seemed almost entirely composed of blood-vessels, as the liver and
brain, and those which showed scarcely a trace of vessels, as cartilage
and bone; it seemed supported also by the appearance of blood-vessels
in all new formations, and by the idea of the blood as the nutrient
fluid. Then came the cell-doctrine, and the belief that the cell was
the really ultimate morphological element--which may be true--and that
“here alone there is any manifestation of life to be found, so that
we must not transfer the seat of vital action anywhere beyond the
cell,”[25]--which is very questionable.
71. We have already seen that the cell is an anatomical element, or
organite; the organism is but an aggregate of organites _and_ their
plasmodes. But Biology, which deals with the organism as a whole, and
with functions which are the resultants of all the vital properties,
must not be restricted to any single factor, however important.
It would assuredly be deemed absurd to say that diamond rings and
lead-pencils were the same, because the diamond and the plumbago,
which are the specific elements of each, are both the same chemical
element,--carbon. The substance is really different in diamond and
plumbago, is different in properties, and is, in rings and pencils,
united with different substances into objects having very different
properties. Whatever analysis may discover as to the identities of
organic structures, we cannot explain a single vital phenomenon
without taking into account the three terms, Structure, Aliment,
and Instrument; and whenever a cell is said to be the seat of vital
action, these three terms must be implied. In Dr. Beale’s hypothesis
the restriction is carried to its extreme; not content with the cell,
he withdraws vital action from the cell as a whole, assigning it to
the protoplasm and nucleus--cell-contents and cell-wall being, in his
view, dead. If it be true that the protoplasm is alone concerned in
Nutrition, yet Nutrition is not Life. Occupied mainly with formative
processes, it leaves other indispensable processes to other parts. He
instances the removal of all the tissues during the metamorphoses of
insects:--“new organs and textures are laid down afresh and developed
_ab initio_, instead of being built up upon those first formed.” But to
show how he restricts the idea of Life, he adds: “Such complete change,
however, necessitates a state of existence during which _action_ or
_function remains in complete abeyance_.”[26]
The muscles and nerves which are instrumental in this functional life
are said to be dead. It is true that the muscle-fibre does not develop
fresh fibres. But it is equally true that the protoplasm of muscle does
not alone execute _muscular_ contraction. Each has its special office.
Hence I reject the idea that formed material is dead. He further says
“formed material may _be_ changed, it cannot _change_ itself.” The
antithesis is doubly inexact: 1°, nothing changes itself, but only
yields to pressure, or reacts on being stimulated; and 2°, all the
evidence at hand is against the notion that the formed material is
not the seat of incessant molecular change; it is wasted and repaired
molecule by molecule. Kölliker properly protests against the growing
tendency of histologists to deify protoplasm, and to make it the sole
seat of vital changes, the cell-wall and cell-products having also, he
says, their physiological importance. It is manifestly erroneous to
deny vital changes to the red blood-corpuscles on the ground of their
no longer containing germinal matter.[27]
72. The analytical view may separate certain parts as active, and
other parts as passive, and thus regard the cells as the seats of
vital activity, the intercellular substance as merely accessory and
instrumental; but the real or synthetical view must recognize both
parts as equally indispensable, equally vital. Take cartilage, for
instance, with its enormous preponderance of intercellular substance
(formed material), and consider how absolutely impossible any of its
uses would be were it reduced to the germinal matter of its corpuscles!
And so of all the tissues.
73. If formed material is not to be excluded from the living parts of
the organism, neither is the plasmode, out of which the germinal matter
arises, since here we have the nutritive changes in their highest
activity; and because the property of Nutrition is here most active,
the other property of Development is in abeyance. Dr. Beale holds that
pabulum necessarily becomes germinal matter; but when we come to treat
of Nutrition it will appear that this is not more true than that Food
necessarily becomes Tissue: some of it does; but much of it is used up
for heat and other purposes.
74. What is true and important in the distinction between germinal
matter and formed material is, that from the former onwards there is a
gradual process of devitalization, the older parts of every organite
and tissue approaching more and more to the state of inorganic matter.
But to show how vain is the attempt to restrict Vitality to any one
out of a complex of co-operant factors, we might set up a chemical
hypothesis to the effect that Vitality depends on phosphates, and
with it explain the phenomena quite as well as with the hypothesis of
germinal matter. For not only is it found that the productive quality
of a soil depends on its richness in phosphates, but, as Lehmann has
shown, wherever cells and fibres make their appearance phosphates
are found, even in the lowest organisms, which, however, contain but
little. Phosphates abound in seeds and ova, in muscles and ganglia,
and are deficient in the woody parts of plants and the elastic fibres
of animals. The infant absorbs phosphates in large quantities and
excretes them in small quantities. Nervous activity is accompanied
by the consumption of a third more phosphorus than accompanies
muscular activity. Phosphates are among the most energetic of organic
stimulants. But who would endow the phosphates with Vitality, on the
ground of their indispensable presence in all vital processes?
75. Life, as we saw, is the expression of the whole organism. Many of
the parts are incapable of manifesting any vital phenomena except in
connection with all the rest; and of those parts which may be separated
from the organism and continue to manifest some vital phenomena, none
are capable of manifesting all. When the connexus of the parts is
destroyed the organism is dead. Long after that cessation which we call
Death, there are still evidences of Vitality in some of the parts:
the heart will continue to beat, the glands will secrete, the hair
will grow, the temperature will still be above that of the surrounding
medium, the muscles will be excitable; these vital properties are
the activities of organized substances, and so long as the state of
organization is preserved they are preserved; but the Life, which
is the synthesis of all the vital properties, vanishes with the
destruction of that synthesis.
76. May we not generalize this, and say that every special form of
existence, organic or inorganic, is determined by the synthesis of its
elements? Atoms are grouped into molecules, molecules into masses,
masses into systems. Out of the textureless germinal membrane and
the yolk, with no additions from without except oxygen and heat,
are developed all the textures and organs of the chick; and this
chick weighs no more than the egg out of which it was evolved. The
development has been a succession of syntheses--epigenesis upon
epigenesis. We may, if we please, regard each organite, as it appears,
living its separate life, and each tissue its separate life; but we
must not confound under the same symbol modes of existence so widely
different as the activities of an organite, and the activities of an
organism constituted by millions of organites.
77. If therefore we cannot restrict Life to the processes of Nutrition,
Dr. Beale’s hypothesis, whatever value it may have as explaining
histogenesis, is quite unacceptable. Neither Vital Force nor Bioplasm
covers the whole ground. For the former there is no better evidence
than our ignorance of the real synthesis; for the latter the evidence
is positive in its nature, but its interpretation is questionable. Dr.
Beale selects as the germinal matter those portions of tissue which
are susceptible of being deeply stained by the carmine solution, the
formed material being only stained in a faint degree; the nucleus
and nucleolus are the portions of germinal matter which are most
deeply stained; and hence he concludes that the older the matter the
fainter will be its coloration. There is no dispute as to the value
of the staining process, invented by Gerlach, for the discrimination
of chemically different parts of a tissue; and Dr. Beale has made
excellent use of it in his researches.[28] But I altogether dispute
the conclusion that the staining process reveals the parts which are
exclusively vital; and for this reason: it depends solely on the acid
reaction of those parts; and we cannot divorce the acid from the
alkaline agencies, both being indispensable. Nay, it has been proved
that in the _living animal_ no organized substance can be stained. Lord
Godolphin Osborne first discovered, in 1856, that the protoplasm of
growing wheat was susceptible of coloration;[29] but Gerlach, in 1858,
found that this never took place in the _animal_ during life. He kept
tadpoles and intestinal worms for weeks in colored fluids, without a
single spot becoming stained; although no sooner did these animals die
than the staining began. Nor even when he injected the colored fluids
under the skin and into the stomach, was the slightest coloration
produced.[30]
To Gerlach’s testimony may be added that of Stein, who, in his
magnificent work on _Infusoria_, says that not only has no foreign
substance ever been found in the protoplasm of the _Opalina_, but
in the _Acineta_, and all the embryos of the higher Infusoria known
to him, he has been unable to color the living substance.[31] This
resistance of the living protoplasm is surely a serious objection
to the hypothesis that only those parts of the dead organism which
are stained were the truly vital parts. Ranke sums up the results
of his experiments thus: “They all show that the living cell resists
the imbibition of every substance which it cannot assimilate. It is
precisely the impossibility of staining the cell that proves this
conclusively, since every particle of carmine absorbed would have
revealed its presence.”
It is not to be supposed that Dr. Beale was unacquainted with Gerlach’s
experiments. He has at any rate so far qualified the statement of his
hypothesis as to admit that it is only after death that the germinal
matter is stained. “The living matter” (he says, _How to Work with the
Microscope_, p. 107) “possesses an acid reaction, or to speak more
correctly, an acid reaction is always developed immediately after its
death.” Now, since this acid reaction only presents itself after death,
and it is this which is revealed by the carmine, we have no right to
conclude that the carmine singles out the vital parts. Every one knows
that the living muscle and nerve, when in repose, present an alkaline
or faintly neutral reaction, and after excitation this is changed into
an acid reaction, which increases with the exhaustion of the tissue. In
strict logic, therefore--if we could logically apply such a test--it
is the unstained parts that ought to be called vital. But, in truth,
alkalinity and acidity are equally indispensable.
78. The main object of my bringing this question forward was to
illustrate the danger of being misled by analysis: a danger we shall
see to be very serious in psychological inquiries. The aid derived from
analysis need never be undervalued; all that we have to bear in mind is
that it is only a logical artifice, and that our real explanation must
always be synthetic. Because of the tendency to rely on analysis there
has been an imperfect discrimination of the profound difference between
ORGANISMS AND MACHINES;
and while on the one hand the legitimate striving of the biologist
to display the mechanism of organic actions has been denounced by a
certain school as Materialism and a hateful attempt to “rob Life of
its mystery,” there has been on the other hand a misconception of this
mechanism, as if its dependent actions were of the nature of machines,
that is to say, as if organized mechanisms were strictly comparable
with machines constructed of inorganic parts. No doubt the laws of
Mechanics are the same in both, for these are abstract laws which take
no account of concrete differences. But when elaborate parallels are
drawn up between steam-engines and animal organisms, the coal consumed
in the one likened to the food in the other, and the force evolved in
the combustion in both being the same, there is a complete obliteration
of all that specially distinguishes vital activity.
79. Between an organism and a machine there is the superficial
resemblance that both have a complex structure, and are constructed of
different and dependent parts. But underneath this resemblance there
is a radical diversity.[32] The arrangement of parts in the organism
is more than a _juxtaposition_, it is a _solidarity_, arising from
the fact of their being all differentiations from a common substance
which is a special combination of the three classes of proximate
principles. Thus they are not parts which have been _put together_, but
which have been _evolved_, each out of a pre-existing part, and each
co-operating in the very existence of the other. The machine is made
of independent and primarily unrelated parts; its integrity depends
on the continued preservation of the substance of each part; waste
is here destruction. The organism is constituted by interdependent
and primarily related parts; its integrity depends on the continued
destruction and renovation of their substance; waste is a condition of
vitality. The actions of the machine are _sub_ordinated; the actions
of an organism are _co_-ordinated. The lever moves a wheel, and the
wheel in moving liberates a spring, each transmitting a communicated
impulse, but otherwise each acts independently--no slight modification
in the structure or movement of the wheel will modify the structure or
the movements of the lever, no alteration in the tension of the spring
will affect the structure of the wheel. But in the organism all are
parts of one sympathetic whole; each reacts on each; each is altered
by the other. Not a nerve is stimulated, nor a muscle moved, but the
entire organism is affected. A condensation here is the cause of a
greater imbibition there. The injection of salt or sugar under the skin
of the frog’s leg will produce cataract in its eye. The activity of
a secreting cell in the ovary, or liver, alters the condition of the
brain; the activity of the brain will check the secretion of a gland,
or relax the sphincters of the bladder. When we observe the growth of
horns, or the appearance of the beard, concomitant with the secretion
of spermatic cells--and especially when we observe with these a
surprising change in the physical and moral capabilities and tendencies
of the organism--we understand how the remotest parts of this mechanism
are bound together by one subtle yet all-powerful tie. Nothing of
this is visible in a machine. In a machine the material is so far of
secondary importance that it may be replaced by materials of various
kinds: a pulley may be worked with a hempen cord, a silken cord, or an
iron chain; a wheel may be wood, iron, copper, brass, or steel; the
actions will in each case be similar. Not so the organic mechanism:
the slightest variation, either in composition or intimate structure,
will affect, and may frustrate the organic activity. It is only in the
skeleton that the specific character of the materials may be changed;
and here only in the substitution of one phosphate for another in the
solid masonry.[33]
80. Another marked characteristic of the organism is that it has a
connexus of actions, the simultaneous effect of a continuous evolution,
appearing in stages and ages. And in the animal organism there is a
_consensus_ as well as a _connexus_, through which there is evolution
of Mind; and in the Social Organism an evolution of Civilization.
This consensus forms an intermediate stage through which the animal
actions are sensitive as well as nutritive, and the nutritive are
regulated by the sensitive. It is obvious that nothing like this is to
be found in a machine; and we conclude, therefore, that any view of the
organism which regards its mechanism without taking in these cardinal
characteristics must be radically defective. We no more deny the
existence of mechanical phenomena in denying that the organism is like
a machine, than we deny the existence of chemical phenomena in denying
that Vitality is chemical.
CHAPTER IV.
THE PROPERTIES AND FUNCTIONS.
81. The terms Property and Function are not always used with desirable
precision. There is, however, a marked distinction between the property
which characterizes a tissue in whatever organ the tissue may be found,
and the function which is exhibited by an organ composed of several
tissues. We ought never to speak of a function unless we imply the
existence of a correlative organ; and it is therefore incorrect to
speak of the function of Nutrition, since _all_ the tissues nourish
themselves; but we may speak of certain organs as special instruments
in facilitating Nutrition. Thus also with respiration, usually, but not
accurately, spoken of as the function of the lungs; the lungs being
simply the most effective of the instruments by which the interchange
of gases (which also takes place in every tissue) is facilitated. If
by Respiration we mean Breathing, then, indeed, Respiration is the
function of the lungs; if we mean the absorption of oxygen and the
exhalation of carbonic acid, Respiration is a general property of
vital tissue. A fragment of muscle removed from the body respires, so
long as its organization is intact; but it does not _breathe_--it has
no accessory instruments, nor does it need them. The co-operation of
nerve centres, diaphragm, ribs, circulating system, etc., necessary
in the complex organism to bring the due amount of oxygen to the
tissues, and convey away the carbonic acid, is here needless. In
the ascending animal series we find this necessity growing with the
complexity of the organism. The whole skin respires in the amphibia,
and to some extent in man also: a frog will live for ten or fourteen
days after extirpation of its lungs, the skin respiring sufficiently
to keep up a feeble vitality. But the skin does not suffice; and, very
early, certain portions are specialized into organs (at first in the
shape of external gills, and finally as internal lungs), for the more
energetic, because more specialized, performance of this office. In the
simpler organisms the blood is easily reached by the air; therefore no
instrument is needed. In primitive societies the transport of goods is
effected by men and women carrying them; in civilized societies by the
aid of horses and camels, and wagons drawn by oxen; till finally these
are insufficient, and railways are created, whose power of transport
transcends the earlier methods, as the breathing of a mammal transcends
the respiration of a mollusc. Breathing is the special function of an
organ--the lungs (or more strictly, the thoracic apparatus)--as Railway
Transport is a special social function. Although each of the tissues
forming this organ can, and does, exhale carbonic acid and absorb
oxygen--and each of the railway servants can, and does, transport
objects to and from the locomotive--yet the main work is thrown upon
the special apparatus.
82. What is meant by properties of tissue and functions of organs
may be thus illustrated. Let us suppose ourselves investigating the
structure of a ship. We find it composed of various _materials_--wood,
iron, copper, hemp, canvas, etc.; and these under various
_configurations_ are formed into particular parts serving particular
purposes, such as deck, masts, anchor, windlass, chains, ropes, sails,
etc. In all these parts the materials preserve their properties; and
wherever wood or iron may be placed, whatever purpose the part may
serve, the properties of wood and iron are unaffected; and it is
through a combination of these properties that the part is effective;
while through the connection of one part with another the purpose
becomes realized. The purposes to which masts, ropes, or sails are
subservient may be called their functions; and these of course only
exist, _as such_, in the ship. It is the same with the organism. We
find it composed of various Tissues, and these are combined into
various Organs or Instruments.[34] The properties of Tissues remain
the same, no matter into what Organs they may be combined; they
preserve and exert their physical, chemical, and vital properties,
as wood and iron preserve their properties. Each Tissue has its
characteristic quality; and the Organ which is constructed out of a
combination of several Tissues, more or less modified, is effective
solely in virtue of these properties,[35] while the Function of that
organ comes into play through its combination with other organs. For
example, muscular tissue has a vital property which is characteristic
of it, Contractility; and muscles are organs constituted by this
tissue and several others;[36] such organs have the general function
of Contraction, but whether this shall be specially manifested in
the beating of the heart, the winking of the eyelid, the movement
of the chest, or the varied movements of the limbs, will depend on
the _anatomical connections_. The reader unfamiliar with Biology is
requested to pay very particular attention to this point; he will find
many obscurities dissipated if he once lays hold of the “principal
connections.”
82_a_. Although Bichat’s conception was of great value, it was
not sufficiently disengaged from the metaphysical mode of viewing
biological phenomena. Both he and his disciples will be found treating
Properties as entities, and invoking them as _causes_ of the phenomena
instead of recognizing them simply as abstract _expressions_ of the
phenomena. Readers of my First Series will remember how often I have
had occasion to point out this common error: men having baptized
observed facts with a comprehensive name, forget the process of
baptism, and suppose the name to represent a mysterious agency. The
fact that gases combine is expressed in the term affinity; and then
Affinity is understood to be the cause of the combinations. The fact
that bodies tend towards each other is called their gravitation, and
Gravitation is then said to cause the tendency. The doctrine of vital
properties has been thus misunderstood. While no one imagines that
he can operate on affinity otherwise than by operating on the known
conditions under which gases combine, many a biologist and physician
speaks as if he could operate on the Irritability of a tissue, or the
Co-ordination of muscles, by direct action on these abstractions.
Let it be therefore once for all expressly stated that by the property
of a tissue is simply meant the _constant mode of reaction of that
tissue under definite conditions_. The property is not a cause,
otherwise than the conditions it expresses are a cause. And these
conditions are first those of the organized structure itself, and
secondly those of the medium in which it lives. Oxygen unites with
Hydrogen to form water, but only under certain pressures; so likewise
muscles manifest Contractility on being stimulated (that is their mode
of reaction), but only under certain degrees of temperature, humidity,
and a certain chemical composition of the plasmode. The property is
so truly an expression of the co-operant conditions, that it is found
to vary with those conditions, and to vanish when they vary beyond a
certain limit.
An attempt has been made to restrict the notion of a property to an
ultimate fact. Whatever is not reducible to known conditions is to
be accepted as a property. Combustion, for example, is reducible to
the molecular combination of oxygen and some other gas; but this
combination itself is not reducible, and it is therefore christened
affinity. I cannot accept this view. Admitting our inability to say
_why_ gases combine under certain conditions (and in this sense all
facts are inexplicable and ultimate, unless we take the _how_ as
ample explanation of the _why_), I must still say that since affinity
itself depends on the co-operation of known conditions, it is not less
explicable than combustion. But the point is unimportant: what we have
here to settle is the meaning of a property of tissue,--and that is the
mode of reaction which that tissue manifests under constant conditions,
internal and external.
83. The evolution of Life is the evolution of special properties and
functions from general properties and functions. The organism rises in
power as it ramifies into variety. Out of a seemingly structureless
germinal membrane, by successive differentiations certain portions
are set apart for the dominant, or exclusive, performance of certain
processes; just as in the social organism there is a setting apart
of certain classes of men for the dominant or exclusive performance
of offices, which by their co-operation constitute Society. The
soldier fights, but ceases to build or reap, weave or teach; the
mason builds; the agriculturist sows and reaps; the priest and
thinker teach; the statesman governs. In simple societies each
does all, or nearly all; but the social life thus manifested is
markedly inferior to the energetic life of a complex society. So with
organisms. An amœba manifests the general properties of Nutrition,
Reproduction, Sensibility, and Movement. But it has no special organs,
consequently no special functions. The polype has a certain rudimentary
specialization of parts: it has a simple alimentary cavity, and
prehensile tentacles; and although by these it can seize and digest its
prey, it can only do so in a limited way--all the manifold varieties
and power of prehension and digestion observed in more complex
organisms are impossible with such organs as the polype possesses.
84. Differences of structure and connection necessarily bring about
corresponding differences in Function, since Function is the _directed
energy_ of the Properties of tissues. One organ will differ from
another in structure, as the liver from the pancreas, or the kidney
from the spleen; or one organ may closely resemble another but differ
from it only in _connections_, as a sensory and a motor nerve, or an
extensor and a flexor muscle. We must therefore always bear both points
in mind. Every modification, structural or connectional, is translated
by a corresponding modification in the office. The hand and the foot
show this well. The tissues are the same in both, the properties are
the same, and both have the same general function of Prehension; but
their morphological differences carry corresponding differences in
their uses.
Suppose we have a galvanic battery, we know that its electric force
may be variously applied. Two pieces of charcoal fixed to the ends of
its conducting wires give us the electric light; replacing the charcoal
by a telegraphic apparatus we can transmit a message from one continent
to the other; the wires dipped in a solution effect a chemical
decomposition, dipped into a mixture of gases they effect a chemical
composition. In these, and many other applications, the property of the
battery is constant; but the functions it subserves have varied with
the varying co-operants. So with the properties of tissue.[37] Not only
have we to bear in mind the organic connections of the tissues, but
also the relation of the organs to their media. Swimming and Walking,
for example, are both functions of the locomotive apparatus, but they
are specially differenced by the media in which the animal moves.
85. The properties of tissues are their peculiar modes of reaction, and
each tissue has its dominant characteristic, such as the Contractility
of the muscle, and the Neurility of the nerve. But there has of late
years sprung up a misleading conception, partly a consequence of the
cell-theory, and partly of the almost inevitable tendency of analysis
to disregard whatever elements it provisionally sets aside; this
conception is the removal of the property from its _tissue_, and the
localization of it in one of the _organites_--cell or fibre. This has
been conspicuously mischievous in the case of the nerve-cell, which has
been endowed with mysterious powers, and may be said to have usurped
the place of nerve-tissue. I shall have to speak of this in the next
problem. Here I only warn the student against the common error. The
properties of a tissue depend on the structure and composition of
that tissue, together with its plasmode and products; they vary as
these vary. To select any one element in this complex, and ascribe the
reaction of the tissue to that, is only permissible as a shorthand
expression.
86. What has just been expounded may be condensed in the following
biological law:--
_Identity of tissue everywhere implies identity of property; and
similarity of tissue corresponding similarity of property. Identity
of organic connection everywhere implies identity of function; and
similarity of organic connection similarity of function._
87. This law, first formulated by me in 1859, and then applied to the
interpretation of nervous functions, was so little understood that for
the most part it met with either decided denial or silent neglect;
no doubt because of the general disinclination to admit that the
properties and functions of the spinal cord could be _similar_ to those
of the brain, in correspondence with the similarity of their tissues
and organic connections. Even Professor Vulpian, who adopted it, as
well as my principal interpretations, hesitated, and relapsed into the
orthodox view in assigning three different properties to one and the
same tissue in cord, medulla oblongata, and cerebrum.[38] In the course
of our inquiries we shall so frequently have to invoke this law that I
earnestly beg the reader to meditate upon it, and ask himself upon what
other grounds, save those of structure and connection, the properties
and functions can possibly rest? If on no other, then similarity in
structure and connection by logical necessity involves similarity in
property and function.
DOES THE FUNCTION DETERMINE THE ORGAN?
88. Closely connected with this law, which simply formulates the
self-evident principle that _every action is rigorously determined by
the nature of the agent, and the conditions under which the act takes
place_, is the surprising question whether functions are dependent
upon organs, or organs dependent on functions?--a question which
sometimes takes this shape: Is Life the result of organization, or is
organization the result of Life?
The vitalist, who holds that Life is an extra-organic agent, is logical
in declaring organization to be the consequence of Life;[39] but there
are many organicists who conclude from certain facts that organs are
developed by functions, and that organization is a result of Life.
There seems, however, to be some equivoque here. I cannot otherwise
understand how Mr. Spencer should have written: “There is one fact
implying that Function must be regarded as taking the precedence of
Structure. Of the lowest rhizopods which present no distinctions
of parts, and nevertheless feed and grow and move about, Professor
Huxley has remarked that they exhibit Life without Organization.”[40]
The equivoque here arises from the practice of calling all living
bodies “organisms,” even those destitute of the differentiations
called organs; but if we substitute the term “living body” in lieu of
“organism,” the equivoque will disappear, and Function no longer seem
to precede Structure. Neither Mr. Spencer nor Mr. Huxley would affirm
that Life can be manifested without a living body; and every living
body must have a structure of some sort--unless by structure be meant
a special configuration of parts. The properties of a body, whether it
be simple or complex in structure, result from the properties of its
components; and the vital phenomena vary with these varying components.
The substance of a Rhizopod is indeed simple as compared with that of
higher organisms, but is complex as compared with anorganisms; and
corresponding with this simplicity of structure there is simplicity of
vital function.[41]
89. The _properties_ of steam are exhibited by the kettle on the fire,
no less than by the gigantic engine which animates a manufactory;
but the _uses_ of steam (the functions of the engine) vary with the
varying structure, and the applications of that structure to other
structures. Precisely analogous is the case of the organ and its
function, in relation to the living substance of which it is a peculiar
modification. Vital actions are manifested by a lump of protoplasm; but
these actions are as sharply demarcated from the actions of more highly
organized animals, as the phenomena of a steam-engine are from those of
a teakettle.
90. Mr. Spencer has nowhere defined what he means by Structure, nor
given a definition of Organ, and this neglect makes it difficult
rightly to appreciate his view. But whether we take structure to
signify the _substance_ of the living body, or the _differentiations_
of that substance into separate tissues and organs, in either case
the actions (functions) of which this structure is the agent must be
rigorously determined by it. Mr. Spencer has avowed this in declaring
that the “general physiologist may consider functions in their widest
sense as the correlatives of tissue.” Is this true in the widest sense
and not true in the narrowest? I am puzzled to find him insisting that
“function from beginning to end is the determining cause of structure.
Not only is this manifestly true where the modification of structure
arises by reaction from modification of function; but it is also
true where a modification of structure otherwise produced apparently
initiates a modification of function.” Such language would be
consistent were he a vitalist who believed in a Principle independent
of Matter which shapes matter into organic forms; but as a positive
thinker he can scarcely escape the admission that since Function is the
activity of the Agent (Function in the widest sense being the action
of the whole Organism, and in its narrowest sense the action of the
special Organ) there cannot be an _activity preceding the agent_. I
suspect that he does not always bear in mind the distinction between
Property and Function, and consequently is led into statements at
variance with the principles he professes. As far as I understand the
course of his thought, it runs somewhat thus: With the increased use
of an organ its volume may be increased, its structure altered; this
alteration will, by reaction, cause alterations in other organs, and
thus the result of a change in the habitual activities of an animal
will be an alteration in the arrangement of its parts.
91. We speak loosely of an organ being developed by increased activity;
but this is loose speech, and investigation shows that the organ is not
developed _by_, but accompanies the increased activity, every increment
of activity being necessarily preceded by a corresponding increment
of structure. This is evident _à priori_: the force manifested is
inherent in the structure manifesting it. Thus we ought not to say
“the vascular system furnishes good instances of the increased growth
that _follows_ increased function”; we ought to say, “that _permits_
increased function.” The muscle having a contractile power represented
by 10, expends, we will suppose, 7 units of force in its normal
activity, and these are replaced by its normal nutrition. If from an
extra demand upon it 9 units are expended, the muscle becomes fatigued,
if 10, exhausted, and it will no longer contract, the whole disposable
sum of its contractility being dissipated. During all these stages the
structure of the muscle--or to prevent all equivoque, let us say the
substance of the muscle--has been changing, not indeed in any degree
appreciable to the eye, but appreciable by the more decisive tests of
chemical and physiological reactions. Yet inasmuch as in the ordinary
course of things the waste is quickly repaired, the muscle in repose
once more regains its original state, once more represents 10 units of
contractility. Now let us consider what takes place when extra labor
is thrown upon the muscle, when exercise causes growth. At the outset
of a walking tour we may not be able to compass more than twenty miles
a day, at its close we manage thirty. Is it the increased activity
of the function which has caused this increase of structure? In one
sense, yes; but let us understand it. Had the increase of activity
been temporary, there would have been only a temporary increase of
structure. But when the ordinary expenditure of 7 units rises to 9,
on several successive days, this extra expenditure of tissue has had
to be met by an extra nutrition--i. e. more plasmode has been formed
and more protoplasm. It is a physiological law, easily explained,
that, within due limits, extra waste brings about extra repair: as the
channels are widened and multiplied, the _derived_ currents become
stronger, and the increased flow of nutrition which was temporary
becomes permanent, because this increase is no longer dependent on an
extra stimulus, but on an enlarged channel.[42] When the channels have
not become multiplied or enlarged, which must be the case whenever the
extra stimulus is fluctuating and temporary, the extra expenditure is
not followed by increased size of the muscle: the currents resume their
old directions, no longer being diverted.
92. Let the social organism furnish us with an illustration. At the
present moment there is a movement against the retail shopkeepers of
London in favor of Co-operative Stores. The stimulus of getting better
goods and cheaper, attracts the flow of custom from its old channels;
and if this continue a certain time the new arrangements will be so
thoroughly organized, and will work so easily, that Co-operative Stores
will to a great extent supplant the retail shops. But if from any
causes the stimulus slackens before this reorganization has passed from
the oscillating into the permanent stage--if the goods are not found
to be superior, or the cheapness not worth the extra trouble--the old
influences (aiding our indolence) which have been long and continuously
at work, will cause the social organism to resume its old aspect,
and the co-operative “varieties” will disappear, or exist beside the
ancient “species.”
In the one case as in the other a glance at the process is enough
to detect that the increase in the activity has been preceded by
a corresponding increase in the structure. The muscle has not been
enlarged _by_ extra activity, but _with_ it. The co-operative action
has grown with each additional co-operator. Looking at the cases from
afar we may justly say that development has been due to function; but
looking to the process we see that each increment of activity was
necessarily dependent on an increment of substance. When changes of
habit or adaptation are said to produce modifications in structures,
this is true in as far as one modification of structure necessarily
brings with it correlative modifications, the growth of one part
affecting the growth of all more or less; but we must remember that
to render the structure capable of new adaptations corresponding
modifications must have been going on. The retail shopkeepers might
securely laugh at the co-operative movement if the respectable families
would not or could not become co-operant. When Mr. Spencer urges that
“not only may leaf-stalks assume to a great degree the character of
stems when they have to discharge the functions of stems by supporting
many leaves, and very large leaves, but they may assume the characters
of leaves when they have to undertake the functions of leaves,” I would
ask if he is not reversing the actual process? The stem cannot assume
the functions of a leaf until it has first assumed the character of a
leaf. The assumptions of both must be gradual, and _pari passu_.
93. The hand is an organ, its function is prehension. The performance
of this function in any of its numerous applications is rigorously
limited by the structure of the hand--the bones, muscles, nerves,
circulating and absorbent vessels, connective tissue, fat, etc. Fatigue
the nerve, and the function will be feebly performed; exhaust it,
and the function ceases; diminish the action of the heart, tie an
artery, or vitiate the structure of the blood, and the function will
be correspondingly affected; stiffen the tendons, soften the bones,
diminish the synovial fluid, or increase the fat--in short, make _any_
alteration whatever in the structure of the hand, and an alteration
is necessarily produced in its function. So rigorously is function
dependent upon structure, that the hand of one man will execute
actions which are impossible to another. The hand of a baby is said to
be the same in structure as the hand of a man; and since the powers
(functions) of the two are notoriously different, we might rashly
conclude that here function was dissociated from structure. The case is
illustrative. In baby and man the structure is similar, not the same;
the resemblance is of kind, not of degree; and the function likewise
varies with the degree. The penny cannon which delights the child is
similar in structure to the ten-pounder which batters down walls; and
though, speaking generally, we may say that the function of both is to
fire gunpowder for human ends, no one expects the penny cannon to be
employed in warfare. In physiology, as in mechanics, the effect varies
with the forces involved.
There can be no doubt that an exaggerated activity will produce a
modification in the active organ, for this is only the familiar case of
increased growth with increased exercise, and this is the biological
meaning in which Function can be said not, indeed, to _create_, but to
_modify_ an existing Organ. Preceding the activity there must be the
agent. Every organ although having its special function has also the
properties of all the tissues which constitute it. The function is only
the synthesis of these properties to which a dominant tissue gives a
special character. The eye, for example, though specially characterized
by its retinal sensibility to light, is largely endowed with muscles,
and its movements are essential to Vision. The intestinal canal, again,
though specially characterized by its secretions for the decomposition
of food, has muscles which are essential to Digestion. In many animals,
especially vegetable-feeders, there is an exaggeration of the muscular
activity in certain parts of the intestinal canal which is only
possible through a corresponding development of the muscular tissue, so
that in some birds, crustaceans, and molluscs we find a gizzard, which
is wholly without a mucous membrane to secrete fluids, and which aids
Digestion solely by trituration.
94. Mr. Spencer, as I have already suggested, seems to have been
led into his view by not keeping distinctly present to his mind the
differences between Properties of tissue and Function, the activity
of an organ. “That function takes precedence of structure,” he says,
“seems implied in the definition of Life. If Life consist of inner
actions so adjusted as to balance outer actions--if the actions are
the _substance_ of Life, while the adjustment constitutes its _form_;
then may we not say that the actions formed must come before that which
forms them--that the continuous change which is the basis of function
must come before the structure which brings the function into shape?”
The separation of “actions formed” from “that which forms them” is
inadmissible. An action cannot come _before_ the agent: it is the
agent in act. The continuous change, which is the basis of Vitality,
is a change of molecular arrangements; and the organ which gives a
special _direction_ to the vital activity, e. g. which shapes the
property of Contractility into the function of Prehension, this organ
must itself be formed before it can manifest this function. It is true
that in one sense the organs are formed by, or are differentiated in,
a pre-existent organism; true that the general activity of living
substance must precede the special activity of any organ, as the
expansions of steam must precede any steam-engine action; but the
general activity depends on the general structure; and the special
actions on the special structures. If by Organization we are to
understand not simply organized substance, but a more or less complex
arrangement of that substance into separate organs, the question is
tantamount to asking whether the simplest animals and plants have life?
And to ask the question, whether Life precedes organic substance? is
tantamount to asking whether the convex aspect of a curve precedes
the concave! or whether the motions of a body precede the body! To
disengage ourselves from the complicated suggestions of such a word as
Life, let us consider one of the vital phenomena, Contraction. This
is a phenomenon manifested by simple protoplasm, and by the highly
differentiated form of protoplasm known as muscle. In one sense it
would be correct to say that Contractility as a general property of
tissue precedes Contraction, which is specialized in muscle. But
it would be absurd to say that _muscular_ contraction preceded the
existence of muscle, and formed it. The contractions of the protoplasm
are not the same as muscular contractions any more than the hand of
a baby is the same as a man’s; the general property which both have
in common depends on the substance both have in common; the special
property which belongs to the muscle depends on its special structure.
An infinite activity of the contractile protoplasm would be incompetent
to form a muscle, unless it were accompanied by that peculiar change in
structure which constitutes muscle. The teakettle might boil forever
without producing a steam-engine or the actions of a steam-engine. That
which is true of one function is true of all functions, and true of
Life, which is the sum of vital activities.
95. It is this haziness which made Agassiz “regret to observe that
it has almost become an axiom that identical functions presuppose
identical organs. There never was a more incorrect principle leading
to more injurious consequences.”[43] And elsewhere he argues that
organs can exist without functions. But this is obviously to pervert
the fundamental idea of an organ. “The teeth of the whale which never
eat through the gums, and the breasts of the males of all classes
of mammalia,” are cited by him as examples of such organs without
functions; but in the physiological significance of the term these are
not organs at all. It is no more to be expected that the breasts of
the male should act in lactation, than that the slackened string of a
violin should yield musical tones; but the breasts of the male may be
easily stimulated into yielding milk, and the slackened string of the
violin may be tightened so as to yield tone. Even the breasts of the
female do not yield milk except under certain conditions, and in the
absence of these are on a par with those of the male.
96. Organized substance has the general properties of Assimilation,
Evolution, Sensibility, and Contractility; each of the special
tissues into which organized substance is differentiated manifests a
predominance of one of these properties. Thus although the embryo-cells
all manifest contractility, it is only the specialized muscle-cell
which continues throughout its existence to manifest this property,
and in a dominant form; the muscle-cell also assimilates and develops,
but besides having these properties in common with all other cells, it
has the special property of contracting with an energy not found in
the others. All cells respire; but the blood-cells have this property
of absorbing oxygen to a degree so far surpassing that of any other
cell that physiologists have been led to speak of their containing a
peculiar respiratory substance. In like manner all, or nearly all,
the tissues contain _myeline_--which indeed is one of the chief
constituents of the yolk of eggs--but only in the white sheath of the
nerves is it detached and specialized as a tissue.
97. But while Sensibility and Contractility are general properties
of organized substance, specialized in special tissues; Sensation
and Contraction are functions of the organs formed by such tissues;
and these organs are only found in animal organisms. It is a serious
error, which we shall hereafter have to insist on, to suppose that
Sensation can be the property of ganglionic cells, or, as it is more
often stated, the property of the central gray matter. Sensation is
the function of the organism; it varies with the varying organ; the
sensation of Touch not being the same as the sensation of Sight, or of
Sound.
98. We may consider the organism under two aspects--that of Structure
and that of Function. The latter has two broad divisions corresponding
with the vegetal and animal lives; the one is Nutrient, the other
Efficient. The one prepares and distributes Food, the other distributes
Motion. Of course this separation is analytical. In reality the two are
interblended; and although the neuro-muscular system is developed out
of the nutritive system, it is no sooner developed than it plays its
part as Instrument in the preparation and distribution of Aliment.
This not being a treatise on Physiology, there can be no necessity for
our here considering the properties and functions in detail. What is
necessary to be said on Sensibility and Contractility will find its
place in the course of future chapters; for the present we will confine
ourselves to Evolution on account of its psychological, no less than
its physiological, interest.
CHAPTER V.
EVOLUTION.
99. That organized substance has the property of nourishing itself
by assimilating from its internal medium substances there present in
an unorganized state, and that this is followed by a development or
differentiation of structure, is familiar to every inquirer.
Every one who has pursued embryological researches, and in a lesser
degree every one who has merely read about them, must have been
impressed by this marvel of marvels: an exceedingly minute portion
of living matter, so simple in aspect that a line will define it,
passes by successive modifications into an organism so complex that a
treatise is needed to describe it; not only do the cells in which the
ovum and the spermatozoon originate, pass into a complex organism,
reproducing the forms and features of the parents, and with these
the constitutional peculiarities of the parents (their longevity,
their diseases, their mental dispositions, nay, their very tricks and
habits), but they may reproduce the form and features, the dispositions
and diseases, of a grandfather or great-grandfather, which had lain
dormant in the father or mother. Consider for an instant what this
implies. A microscopic cell of albuminous compounds, wholly without
trace of organs, not appreciably distinguishable from millions of other
cells, does nevertheless contain within it the “possibilities” of an
organism so complex and so special as that of a Newton or a Napoleon.
If ever there was a case when the famous Aristotelian notion of a
“potential existence” seemed justified, assuredly it is this. And
although we can only by a fallacy maintain the oak to be _contained_
in the acorn, or the animal contained in the ovum, the fallacy is so
natural, and indeed so difficult of escape, that there is no ground
for surprise when physiologists, on first learning something of
development, were found maintaining that the perfect organism existed
already in the ovum, having all its lineaments in miniature, and only
growing into visible dimensions through the successive stages of
evolution.[44] The preformation of the organism seemed an inevitable
deduction from the opinions once universal. It led to many strange,
and some absurd conclusions; among them, to the assertion that the
original germ of every species contained within it all the countless
individuals which in process of time might issue from it; and this in
no metaphysical “potential” guise, but as actual boxed-up existences
(_emboîtés_); so that Adam and Eve were in the most literal sense
progenitors of the whole human race, and contained their progeny
already shaped within them, awaiting the great accoucheur, time.
100. This was the celebrated “emboîtement” theory. In spite of obvious
objections it gained scientific acceptance, because physiologists could
not bring themselves to believe that so marvellous a structure as that
of a human organism arose by a series of successive modifications, or
because they could not comprehend how it was built up, part by part,
into forms so closely resembling the parent-forms. That many and
plausible reasons pleaded in favor of this opinion is evident in the
fact that illustrious men like Haller, Bonnet, Vallisneri, Swammerdamm,
Réaumur, and Cuvier, were its advocates; and if there is not a sigle
physiologist of our day who accepts it, or who finds any peculiar
difficulty in following the demonstrations of embryologists, how from
the common starting-point of a self-multiplying epithelial cell parts
so diverse as hairs, nails, hoofs, scales, feathers, crystalline lens,
and secreting glands may be evolved, or how from the homogeneous
germinal membrane the complex organism will arise, there are very
few among the scorners of the dead hypothesis who seem capable of
generalizing the principles which have destroyed it, or can conceive
that the laws of Evolution apply as rigorously to the animal and
vegetable _kingdoms_ as to the individual _organisms_. The illustrious
names of those who advocated the preformation hypothesis may serve to
check our servile submission to the authorities so loudly proclaimed as
advocates of the fixity of species. The more because the two doctrines
have a common parentage. The one falls with the other, and no array of
authorities can arrest the fall. That the manifold differentiations
noticeable in a complex organism should have been evolved from a
membrane wholly destitute of differences is a marvel, but a marvel
which Science has made intelligible. Yet the majority of those to
whom this has been made intelligible still find an impossibility in
admitting that the manifold forms of plant and animal were successively
evolved from equally simple origins. They relinquish the hypothesis of
preformation in the one case, and cling to it in the other. Evolution,
demonstrable in the individual history, seems preposterous in the
history of the class. And thus is presented the instructive spectacle
of philosophers laughing at the absurdities of “preformation,” and
yet exerting all their logic and rhetoric in defence of “creative
fiats”--which is simply the preformation hypothesis “writ large.”
101. It would not be difficult to show that the doctrine of
Epigenesis, with which Wolff forever displaced the doctrine of
Preformation, leads by an inevitable logic to the doctrine of universal
Evolution; and that we can no more understand the appearance of a
new organism which is not the modification of some already existing
organism, than we can understand the sudden appearance of a new organ
which is not the modification of some existing structure. In the one
case as in the other we may disguise the process under such terms as
creative fiat and preformation; but these terms are no explanations;
they re-state the results, they do not describe the process; whereas
Epigenesis describes the process as it passes under the eye of science.
102. If any reader of these pages who, from theological or zoölogical
suspicion of the Development Hypothesis, clings to the hypothesis
of a creative Plan which once for all arranged the organic world in
Types that could not change, will ask what rational interpretation can
be given to the succession of phases each embryo is forced to pass
through, it may help to give him pause. He will observe that _none_ of
these phases have any adaptation to the future state of the animal, but
are in positive contradiction to it, or are simply purposeless; whereas
all show stamped on them the unmistakable characters of _ancestral_
adaptations and the progressions of Organic Evolution. What does the
fact imply? There is not a single known example of a complex organism
which is not developed out of simpler forms. Before it can attain the
complex structure which distinguishes it, there must be an evolution of
forms similar to those which distinguish the structures of organisms
lower in the series. On the hypothesis of a Plan which prearranged
the organic world, nothing could be more unworthy of a supreme
intelligence than this inability to construct an organism at once,
without previously making several tentative efforts, undoing to-day
what was so carefully done yesterday, and _repeating for centuries the
same tentatives, and the same corrections, in the same succession_. Do
not let us blink this consideration. There is a traditional phrase much
in vogue among the anthropomorphists, which arose naturally enough from
the tendency to take human methods as an explanation of the divine--a
phrase which becomes a sort of argument--“The Great Architect.” But
if we are to admit the human point of view, a glance at the facts of
embryology must produce very uncomfortable reflections. For what should
we say to an architect who was unable, or being able was obstinately
unwilling, to erect a palace except by first using his materials in the
shape of a hut, then pulling it down and rebuilding them as a cottage,
then adding story to story and room to room, _not_ with any reference
to the ultimate purposes of the palace, but wholly with reference to
the way in which houses were constructed in ancient times? What should
we say to the architect who could not form a museum out of bricks
and mortar, but was forced to begin as if going to build a mansion:
and after proceeding some way in this direction, altered his plan
into a palace, and that again into a museum? Yet this is the sort of
succession on which organisms are constructed. The fact has long been
familiar; how has it been reconciled with Infinite Wisdom? Let the
following passage answer for a thousand:--“The embryo is nothing like
the miniature of the adult. For a long while the body in its entirety
and its details presents the strangest of spectacles. Day by day and
hour by hour the aspect of the scene changes, and this instability is
exhibited by the most essential parts no less than by the accessory
parts. One would say that Nature feels her way, and only reaches the
goal after many times missing the path,--on dirait que la nature
tâtonne et ne conduit son œuvre à bon fin qu’après s’être souvent
trompée.”[45] Writers have no compunction in speaking of Nature feeling
her way and blundering; but if in lieu of Nature, which may mean
anything, the Great Architect be substituted, it is probable that the
repugnance to using such language of evasion may cause men to revise
their conceptions altogether; they dare not attribute ignorance and
incompetence to the Creator.
103. Obviously the architectural hypothesis is incompetent to explain
the phenomena of organic development. Evolution is the universal
process; not creation of a direct kind. Von Baer, who very properly
corrected the exaggerations which had been put forth respecting the
identity of the embryonic forms with adult forms lower in the scale,
who showed that the mammalian embryo never was a bird, a reptile,
or a fish, nevertheless emphasized the fact that the mammalian
embryo passes through all the lower typical forms; so much so that,
except by their size, it is impossible to distinguish the embryos of
mammal, bird, lizard, or snake. “In my collection,” he says, “there
are two little embryos which I have omitted to label, so that I am
now quite incompetent to say to what class they belong. They may be
lizards, they may be small birds, or very young mammals; so complete
is the similarity in the mode of formation of the head and trunk.
The extremities have not yet made their appearance. But even if they
existed in the earliest stage we should learn nothing from them, for
the feet of lizards, mammals, and the wings of birds, all arise from
the same common form.” He sums up with his formula: “The special type
is always evolved from a more general type.”[46]
Such reminiscences of earlier forms are intelligible on the supposition
that originally the later form was a modification of the earlier form,
and that this modification is repeated; or on the supposition that
there was a similarity in the organic conditions, which similarity
ceased at the point where the new form emerged. But on no hypothesis
of creative Plan are they intelligible. They are useless structures,
failing even to subserve a temporary purpose. Sometimes, as Mr. Darwin
remarks, a trace of the embryonic resemblance lasts till a late age:
“Thus birds of the same genus, and of closely allied genera, often
resemble each other in their first and second plumage: as we see in
the spotted feathers in the thrush group. In the cat tribe most of the
species are striped and spotted in lines; and stripes or spots can
plainly be distinguished in the whelp of the lion and the puma. We
occasionally, though rarely, see something of this kind in plants....
The points of structure in which the embryos of widely different
animals of the same class resemble each other often have no direct
relation to their conditions of existence. We cannot, for instance,
suppose that in the embryos of the vertebrata the peculiar loop-like
courses of the arteries near the bronchial slits are related to similar
conditions in the young mammal which is nourished in the womb of its
mother, in the egg of a bird which is hatched in a nest, and in the
spawn of a frog under water.”
104. It would be easy to multiply examples, but I will content myself
with three. The tadpole of the Salamander has gills, and passes his
existence in the water; but the _Salamandra atra_, which lives high
up among the mountains, brings forth its young full-formed. This
animal never lives in the water. Yet if we open a gravid female, we
find tadpoles inside her with exquisitely feathered gills, and (as I
have witnessed) these tadpoles “when from the mother’s womb untimely
ripped,” if placed in water, swim about like the tadpoles of water
newts. Obviously this aquatic organization has no reference to the
future life of the animal, nor has it any adaptation to its embryonic
condition; it has solely reference to ancestral forms, it repeats a
phase in the development of its progenitors. Again, in the embryo of
the naked Nudibranch, we always observe a shell, although the animal
is without a shell, and there can be no purpose served by the shell in
embryonic life.[47] Finally, the human embryo has a tail, which is of
course utterly purposeless, and which, although to be explained as a
result of organic laws, is on the creative hypothesis only explained as
an adherence to the general plan of structure--a specimen of pedantic
trifling “worthy of no intellect above the pongo’s.”[48]
105. Humanly appreciated, not only is it difficult to justify the
successive stages of development, the incessant building up of
structures immediately to be taken down, but also to explain why
development was necessary at all. Why are not plants and animals
formed at once, as Eve was mythically affirmed to be taken from Adam’s
rib, and Minerva from Jupiter’s head? The theory of Evolution answers
this question very simply; the theory of Creation can only answer
it by affirming that such was the ordained plan. But the theory of
Evolution not only gives the simpler and more intelligible answer to
this question, it gives an answer to the further question which leaves
the theory of Creation no loophole except a sophism--namely, why the
formation of organisms is constantly being frustrated or perverted?
And, further, it gives an explanation of the law noticed by Milne
Edwards, that Nature is as economical in her means as she is prodigal
in her variation of them: “On dirait qu’avant de recourir à des
ressources nouvelles elle a voulu épuiser, en quelque sorte, chacun
des procédés qu’elle avait mis en jeu.”[49] The applause bestowed on
Nature for being economical is a curious transference to Nature of
human necessities. Why, with a whole universe at her disposal, should
Nature be economical? Why must she always be working in the same
groove, and using but a few out of the many substances at her command?
Economy is a virtue only in the poor. If Nature, in organic evolutions,
is restricted to a very few substances, and a very few modes of
combination, always creating new forms by modification of the old, and
apparently incapable of creating an organism at once, this must imply
an inherent necessity which is very unlike the free choice that can
render economy a merit.
106. There may indeed be raised an objection to the Development
Hypothesis on the ground that if the complex forms were all developed
from the simpler forms, we ought to trace the identities through all
their stages. If the fish developed into the reptile, the reptile
into the bird, and the bird into the mammal (which I, for one, think
questionable), we ought to find, it is urged, evidence of this passage.
And at one time it was asserted that the evidence existed; but this
has been disproved, and on the disproof the opponents of Evolution
take their stand. Although I cannot feel much confidence in the idea
of such a passage from Type to Type, and although the passage, if ever
it occurred, must have occurred at so remote a period as to leave
no evidence more positive than inference, I cannot but think the
teaching of Embryology far more favorable to it than to our opponents.
Supposing, for the sake of argument, that the passage did take place,
ought we to find the embryonic stages accurately reproducing the
permanent forms of lower types? Von Baer thinks we ought; and lesser
men may follow him without reproach. But it seems to me that he starts
from an inadmissible assumption, namely, that the development must
necessarily be in a straight line rather than in a multiplicity of
divergent lines. “When we find the embryonic condition,” he says,
“differing from the adult, we ought to find a corresponding condition
somewhere in the lower animals.”[50] Not necessarily. We know that
the mental development of a civilized man passes through the stages
which the race passed through in the course of its long history, and
the psychology of the child reproduces the psychology of the savage.
But as this development takes place under conditions in many respects
different, and as certain phases are hurried over, we do not expect
to find a complete parallel. It is enough if we can trace general
resemblances. Von Baer adds, “That certain correspondences should occur
between the embryonic states of some animals and the adult states of
others seems inevitable and of no significance(?). They could not fail,
since the embryos lie within the animal sphere, and the variations
of which the animal body is capable are determined for each type by
the internal connection and mutual reaction of its organs, so that
particular repetitions are inevitable.” A profound remark, to which I
shall hereafter have occasion to return, but its bearing on the present
question is inconclusive. The fact that the embryonic stages of the
higher animals resemble in general characters the permanent stages
of the lower animals, and very closely resemble the embryonic stages
of those animals, is all that the Development Hypothesis requires.
Nor is its value lessened by the fact that many of the details and
intermediate stages seem passed over in the development of the higher
forms, for the recapitulation can only be of outlines, not of details;
since there are differences in the forms, there must be differences in
their histories.
107. In the preceding observations the object has simply been to show
that the phenomena to be explained can be rationally conceived as
resulting from gradual Evolution, whereas they cannot be so rationally
interpreted on any other hypothesis. And here it may be needful to say
a word respecting Epigenesis.
The Preformation hypothesis, which regarded every organism as a simple
educt and not the product of a germ, was called by its advocates an
evolution hypothesis--meaning that the adult form was an outgrowth of
the germ, the miniature magnified. Wolff, who replaced that conception
by a truer one, called his, by contrast, Epigenesis, meaning that
there was not simply _out_-growth but _new_ growth. “The various
parts,” he says, “arise one _after_ the other, so that always one is
secreted from (_excernirt_), or deposited (_deponirt_) on the other;
and then it is either a free and independent part, or is only fixed
to that which gave it existence, or else is contained within it. So
that _every part is the effect of a pre-existing part, and in turn
the cause of a succeeding part_.”[51] The last sentence expresses
the conception of Epigenesis which embryologists now adopt; and
having said this, we may admit that Wolff, in combating the error
of preformation, replacing it with the truer notion of gradual and
successive formation, was occasionally open to the criticism made
by Von Baer, that he missed the true sense of Evolution, since the
new parts are not _added on_ to the old parts as new formations,
but _evolved from_ them as transformations. “The word Evolution,
therefore, seems to me more descriptive of the process than Epigenesis.
It is true that the organism is not preformed, but the course of its
development is precisely the course which its parents formerly passed
through. Thus it is the Invisible--the course of development--which is
predetermined.”[52] When the word Epigenesis is used, therefore, the
reader will understand it to signify that necessary succession which
determines the existence of new forms. Just as the formation of chalk
is not the indifferent product of any combination of its elements,
carbon, oxygen, and calcium, but is the product of only one series of
combinations, an evolution through necessary successions, the carbon
uniting with oxygen to form carbonic acid, and this combining with the
oxide of calcium to form chalk, so likewise the formation of a muscle,
a bone, a limb, or a joint has its successive stages, each of which
is necessary, none of which can be transposed. The formation of bone
is peculiarly instructive, because the large proportion of inorganic
matter in its substance, and seemingly deposited in the organic tissue,
would lead one to suppose that it was almost an accidental formation,
which might take place anywhere; yet although what is called
connective tissue will ossify under certain conditions, true bone is
the product of a very peculiar modification, which almost always needs
to be preceded by cartilage. That the formation of bone has its special
history may be seen in the fact that it is the last to appear in the
animal series, many highly organized fishes being without it, and all
the other systems appearing before it in the development of the embryo.
Thus although the mother’s blood furnishes all the requisite material,
the fœtus is incapable of assimilating this material and of forming
bone, until its own development has reached a certain stage. Moreover,
when ossification does begin, it generally begins in the skull (in
man in the clavicle); and the only approach to an internal skeleton
in the Invertebrates is the so-called skull of the Cephalopoda.
Not only is bone a late development, but cartilage is also; and
although it is an error to maintain that the Invertebrates are wholly
destitute of cartilage, its occasional presence having been fully
proved by Claparède and Gegenbaur, the rarity of its presence is very
significant. The animals which can form shells of chalk and chitine are
yet incapable of forming even an approach to bone.
108. Epigenesis depends on the laws of succession, which may be likened
to the laws of crystallization, if we bear in mind the essential
differences between a crystal and an organism, the latter retaining
its individuality through an incessant molecular change, the former
only by the exclusion of all change. When a crystalline solution
takes shape, it will always take a definite shape, which represents
what may be called the _direction_ of its forces, the polarity of
its constituent molecules. In like manner, when an organic plasmode
takes shape--crystallizes, so to speak--it always assumes a specific
shape dependent on the polarity of its molecules. Crystallographers
have determined the several forms possible to crystals; histologists
have recorded the several forms of Organites, Tissues, and Organs.
Owing to the greater variety in elementary composition, there is in
organic substance a more various polar distribution than in crystals;
nevertheless, there are sharply defined limits never overstepped, and
these constitute what may be called the specific forms of Organites,
Tissues, Organs, Organisms. An epithelial cell, for example, may be
ciliated or columnar, a muscle-fibre striated or non-striated, a
nerve-fibre naked or enveloped in a sheath, but the kind is always
sharply defined. An intestinal tube may be a uniform canal, or a canal
differentiated into several unlike compartments, with several unlike
glandular appendages. A spinal column may be a uniform solid axis, or
a highly diversified segmented axis. A limb may be an arm, or a leg, a
wing, or a paddle. In every case the anatomist recognizes a specific
type. He assigns the uniformities to the uniformity of the substance
thus variously shaped, under a history which has been similar; the
diversities he assigns to the various conditions under which the
processes of growth have been determined. He never expects a muscular
tissue to develop into a skeleton, a nervous tissue into a gland,
an osseous tissue into a sensory organ. He never expects a tail to
become a hand or a foot, though he sees it in monkeys and marsupials
serving the offices of prehension and locomotion. He never expects
to find fingers growing anywhere except from metacarpal bones, or an
arm developed from a skull. The well-known generalization of Geoffroy
St. Hilaire that an organ is more easily annihilated than transposed,
points to the fundamental law of Epigenesis. In the same direction
point all the facts of growth. Out of a formless germinal membrane we
see an immense variety of forms evolved; and out of a common nutritive
fluid this variety of organs is sustained, repaired, replaced; and
this not indifferently, not casually, but according to rigorous laws
of succession; that which precedes determining that which succeeds
as inevitably as youth precedes maturity, and maturity decay. The
nourishment of various organs from plasmodes derived from a common
fluid, each selecting from that fluid only those molecules that are
like its own, rejecting all the rest, is very similar to the formation
of various crystals in a solution of different salts, each salt
separating from the solution only those molecules that are like itself.
Reil long ago called attention to this analogy. He observed that if
in a solution of nitre and sulphate of soda a crystal of nitre be
dropped, all the dissolved nitre crystallizes, the sulphate remaining
in solution; whereas on reversing the experiment, a crystal of sulphate
of soda is found to crystallize all the dissolved sulphate, leaving the
nitre undisturbed. In like manner muscle selects from the blood its own
materials which are there in solution, rejecting those which the nerve
will select.
109. Nay, so definite is the course of growth, that when a limb or part
of a limb is cut off from a crab or salamander, a new limb or new part
is reproduced in the old spot, exactly like the one removed. Bonnet
startled the world by the announcement that the _Naïs_, a worm common
in ponds, spontaneously divided itself into two worms; and that when he
cut it into several pieces, each piece reproduced head and tail, and
grew into a perfect worm. This had been accepted by all naturalists
without demur, until Dr. Williams, in his “Report on British Annelida,
1851,” declared it to be a fable. In 1858, under the impulse of Dr.
Williams’s very emphatic denial, I repeated experiments similar to
those of Bonnet, with similar results. I cut two worms in half, and
threw away the head-bearing segments, placing the others in two
separate vessels, with nothing but water and a little mud, which was
first carefully inspected to see that no worm lay concealed therein. In
a few days the heads were completely reformed, and I had the pleasure
of watching them during their reconstruction. When the worms were quite
perfect, I again cut away their heads, and again saw these reformed.
This was repeated, till I had seen four heads reproduced; after which
the worms succumbed.
110. The question naturally arises, Why does the nutritive fluid
furnish only material which is formed into a part like the old one,
instead of reproducing another part, or one having a somewhat different
structure? The answer to this question is the key to the chief problem
of organic life. That a limb _in situ_ should replace its molecular
waste by molecules derived from the blood, seems intelligible enough
(because we are familiar with it), and may be likened to the formation
of crystals in a solution; but how is it that the limb _which is not
in existence_ can assimilate materials from the blood? How is it that
the blood, which elsewhere in the organism will form other parts,
here will only form this particular part? There is, probably, no one
who has turned his attention to these subjects who has not paused to
consider this mystery. The most accredited answer at present before the
world is one so metaphysiological that I should pass it by, were it
not intimately allied with that conception of Species, which it is the
object of these pages to root out. It is this:
111. The organism is determined by its Type, or, as the Germans say,
its Idea. All its parts take shape according to this ruling plan;
consequently, when any part is removed, it is reproduced according to
the Idea of the whole of which it forms a part. Milne Edwards, in a
very interesting and suggestive work, concludes his survey of organic
phenomena in these words: “Dans l’organisme tout semble calculé en
vue d’un résultat déterminé, et l’harmonie des parties ne résulte
pas de l’influence qu’elles peuvent exercer les unes sur les autres,
mais de leur co-ordination sous l’empire d’une puissance commune,
d’un plan préconçu, d’une force pré-existante.”[53] This is eminently
metaphysiological. It refuses to acknowledge the operation of immanent
properties, refuses to admit that the harmony of a complex structure
results from the mutual relations of its parts, and seeks _outside_
the organism for some mysterious force, some plan, not otherwise
specified, which regulates and shapes the parts. Von Baer, in his great
work, has a section entitled, “The nature of the animal determines
its development”; and he thus explains himself: “Although every stage
in development is only made possible by the pre-existing condition
[which is another mode of expressing Epigenesis], nevertheless the
entire development is ruled and guided by the Nature of the animal
which is about to be (von der gesammten Wesenheit des Thieres welches
werden soll), and it is not the momentary condition which alone
and absolutely determines the future, but more general and higher
relations.”[54] One must always be slow in rejecting the thoughts
of a master, and feel sure that one sees the source of the error
before regarding it as an error; but in the present case I think the
positive biologist will be at no loss to assign Von Baer’s error to
its metaphysical origin. Without pausing here to accumulate examples
both of anomalies and slighter deviations which are demonstrably due
to the “momentary conditions” that preceded them, let us simply note
the logical inconsistency of a position which, while assuming that
_every separate stage_ in development is the necessary sequence of its
predecessor, declares the _whole of the stages_ independent of such
relations! Such a position is indeed reconcilable on the assumption
that animal forms are moulded “like clay in the hands of the potter.”
But this is a theological dogma, which leads to very preposterous and
impious conclusions; and whether it leads to these conclusions or to
others, positive Biology declines theological explanations altogether.
Von Baer, although he held the doctrine of Epigenesis, coupled it,
as many others have done, with metaphysical doctrines to which it is
radically opposed. He believed in Types as realities; he was therefore
consistent in saying, “It is not the Matter and its arrangements which
determine the product, but the nature of the parent form--the Idea,
according to the new school.” How are we to understand this Idea? If
it mean an independent Entity, an agency external to the organism, we
refuse to acknowledge its existence. If it mean only an _a posteriori_
abstraction expressing the totality of the conditions, then, indeed,
we acknowledge that it determines the animal form; but this is only an
abbreviated way of expressing the law of Evolution, by which each stage
determines its successor. The Type does not _dominate_ the conditions,
it _emerges_ from them; the animal organism is not cast in a mould, but
the imaginary mould is the form which the polarities of the organic
substance assume. It would seem very absurd to suppose that crystals
assumed their definite shapes (when the liquid which held their
molecules in solution is evaporated) under the determining impulse
of phantom-crystals, or Ideas; yet it has not been thought absurd to
assume phantom forms of organisms.
112. The conception of Type as a determining influence arises from
that fallacy of taking a resultant for a principle, which has played
so conspicuous a part in the history of philosophy. Like many others
of its class it exhibits an interesting evolution from the crude
metaphysical to the subtle metaphysical point of view, which at last
insensibly blends into the positive point of view. At first the Type or
Idea was regarded as an objective reality, external to the organism it
was supposed to rule. Then this notion was replaced by an approach to
the more rational interpretation, the idea was made an internal not an
external force, and was incorporated with the material elements of the
organism, which were said to “endeavor” to arrange themselves according
to the Type. Thus Treviranus declares that the seed “dreams of the
future flower”; and “Henle, when he affirms that hair and nails grow in
virtue of the Idea, is forced to add that the parts endeavor to arrange
themselves according to this Idea.”[55] Even Lotze, who has argued
so victoriously against the vitalists, and has made it clear that an
organism is a vital mechanism, cannot relinquish this conception of
legislative Ideas, though he significantly adds, “these have no power
in themselves, but only in as far as they are grounded in mechanical
conditions.” Why then superfluously add them to the conditions? If
every part of a watch, in virtue of the properties inherent in its
substance, and of the mutual reactions of these and other parts,
has a mechanical value, and if the sum of all these parts is the
time-indicating mechanism, do we add to our knowledge of the watch, and
our means of repairing or improving it, by assuming that the parts have
over and above their physical properties the metaphysical “tendency”
or “desire” to arrange themselves into this specific form? When we
see that an organism is constructed of various parts, each of which
has its own properties inalienable from its structure, and its uses
dependent on its relation to other parts, do we gain any larger insight
by crediting these parts with desires or “dreams” of a future result
which their union will effect? That which is true in this conception of
legislative Ideas is that when the parts come together there is mutual
reaction, and the resultant of the whole is something very unlike
the mere addition of the items, just as water is very unlike oxygen
or hydrogen; further, the connexus of the whole impresses a peculiar
direction on the development of the parts, and the law of Epigenesis
necessitates a serial development, which may easily be interpreted as
due to a preordained plan.
113. In a word, this conception of Type only adds a new name to the
old difficulty, adding mist to darkness. The law of Epigenesis,
which is simply the expression of the material process determined by
the polarity of molecules, explains as much of the phenomena as is
explicable. A lost limb is replaced by the very processes, and through
the same progressive stages as those which originally produced it. We
have a demonstration of its not being reformed according to any Idea
or Type which exists apart from the immanent properties of the organic
molecules, in the fact that it is not reformed at once, but by gradual
evolution; the mass of cells at the stump are cells of embryonic
character, cells such as those which originally “crystallized” into
muscles, nerves, vessels, and integument, and each cell passes through
all its ordinary stages of development. It is to be remembered that so
intimately dependent is the result on the determining conditions, that
any external influence which disturbs the normal course of development
will either produce an anomaly, or frustrate the formation of a new
limb altogether. One of my tritons bit off the leg of his female;[56]
the leg which replaced it was much malformed, and curled over the back
so as to be useless; was this according to the Idea? I cut it off, and
examined it; all the bones were present, but the humerus was twisted,
and of small size. In a few weeks a new leg was developed, and this
leg was normal. If the Idea, as a ruling power, determined the growth
of this third leg, what determined the second, which was malformed?
Are we to suppose that in normal growth the Idea prevails, in abnormal
the conditions? That it is the polarity of the molecules which at
each moment determines the group those molecules will assume, is well
seen in the experiment of Lavalle mentioned by Bronn.[57] He showed
that if when an octohedral crystal is forming, an angle be cut away,
so as to produce an artificial surface, a similar surface is produced
spontaneously on the corresponding angle, whereas all the other angles
are sharply defined. “Valentin,” says Mr. Darwin, “injured the caudal
extremity of an embryo, and three days afterwards it produced rudiments
of a double pelvis, and of double hind limbs. Hunter and others have
observed lizards with their tails reproduced and doubled. When Bonnet
divided longitudinally the foot of the salamander, several additional
digits were occasionally formed.”[58] Where is the evidence of the Idea
in these cases?
114. I repeat, the reproduction of lost limbs is due to a process which
is in all essential respects the same as that which originally produced
them; the genesis of one group of cells is the necessary condition
for the genesis of its successor, nor can this order be transposed.
But--and the point is very important--it is not every part that can be
reproduced, nor is it every animal that has reproductive powers. The
worm, or the mollusk, seems capable of reproducing every part; the crab
will reproduce its claws, but not its head or tail; the perfect insect
of the higher orders will reproduce no part (indeed the amputation of
its antennae only is fatal), the salamander will reproduce its leg,
the frog not. In human beings a muscle is said never to be reproduced;
but this is not the case in the rare examples of supplementary fingers
and toes, which have been known to grow again after amputation.
The explanation of this difference in the reproductive powers of
different animals is usually assigned to the degree in which their
organisms retain the embryonic condition; and this explanation is made
plausible by the fact that the animals which when adult have no power
of replacing lost limbs, have the power when in the larval state. But
although this may in some cases be the true explanation, there are
many in which it fails, as will be acknowledged after a survey of the
extremely various organisms at widely different parts of the animal
series which possess the reproductive power. Even animals in the same
class, and at the same stage of development, differ in this respect.
I do not attach much importance to the fact that all my experiments
on marine annelids failed to furnish evidence of their power of
reproducing lost segments; because it is difficult to keep them under
conditions similar to those in which they live. But it is significant
that, among the hundreds which have passed under my observation, not
one should have been found with a head-segment in the process of
development, replacing one that had been destroyed; and this is all the
more remarkable from the great tenacity of life which the mutilated
segments manifest. Quatrefages had observed portions of a worm, after
gangrene had destroyed its head and several segments, move about in the
water and avoid the light![59]
115. A final argument to show that the reproduction is not determined
by any ruling Idea, but by the organic conditions and the necessary
stages of evolution, is seen in the reappearance of a tumor or cancer
after it has been removed. We find the new tissue appear with all the
characters of the normal tissue of the gland, then rapidly assume one
by one the characters of the diseased tissue which had been removed;
and there as on is, that the regeneration of the tissue is accompanied
by the same abnormal conditions which formerly gave rise to the tumor:
the directions of “crystallization” are similar because the conditions
are similar. In every case of growth or regrowth the conditions being
the same, the result must be the same.
116. It seems a truism to insist that similarity in the results must be
due to similarity in the conditions; yet it is one which many theorists
disregard; and especially do we need to bear it in mind when arguing
about Species. I will here only touch on the suggestive topic of the
analogies observed not simply among animals at the extreme ends of the
scale, but also between animals and plants where the idea of a direct
kinship is out of the question.
My very imperfect zoölogical knowledge will not allow me to adduce a
long array of instances, but such an array will assuredly occur to
every well-stored mind. It is enough to point to the many analogies
of Function, more especially in the reproductive processes--to the
existence of burrowers, waders, flyers, swimmers in various classes--to
the existence of predatory mammals, predatory birds, predatory
reptiles, predatory insects by the side of herbivorous congeners,--to
the nest-building and incubating fishes; and in the matter of Structure
the analogies are even more illustrative when we consider the widely
diffused spicula, setæ, spines, hooks, tentacles, beaks, feathery
forms, nettling-organs, poison-sacs, luminous organs, etc.; because
these have the obvious impress of being due to a community of substance
under similar conditions rather than to a community of kinship. The
beak of the tadpole, the cephalopod, the male salmon, and the bird,
are no doubt in many respects unlike; but there is a significant
likeness among them, which constitutes a true analogy. I think there
is such an analogy between the air-bladder of fishes and the tracheal
rudiment which is found in the gnat-larva (_Corethra plumicornis_).[60]
Very remarkable also is the resemblance of the _avicularium_, or
“bird’s-head process,” on the polyzoon known popularly as the Corkscrew
Coralline (_Bugula avicularia_), which presents us in miniature
with a vulture’s head--two mandibles, one fixed, the other moved by
muscles visible within the head. No one can watch this organ snapping
incessantly, without being reminded of a vulture, yet no one would
suppose for a moment that the resemblance has anything to do with
kinship.
117. Such cases are commonly robbed of their due significance by being
dismissed as coincidences. But what determines the coincidence? If we
assume, as we are justified in assuming, that the _possible directions_
of Organic Combination, and the resultant forms, are limited, there
must inevitably occur such coincident lines: the hooks on a Climbing
Plant will resemble the hooks on a Crustacean or the claws of a Bird,
as the one form in which under similar external forces the more solid
but not massive portions of the integument tend to develop. I am too
ill acquainted with the anatomy of plants to say how the hooks so
common among them arise; but from examination of the Blackberry, and
comparison of its thorns with the hooks and spines of the Crustacea,
I am led to infer that in each case the mode of development is
identical--namely, the secretion of chitine from the cellular matrix of
the integument.
Another mode of evading the real significance of such resemblances
is to call them analogies, not homologies. There is an advantage in
having two such terms, but we ought to be very clear as to their
meaning and their point of separation. Analogy is used to designate
similarity in Function with dissimilarity in Structure. The wing
of an insect, the wing of a bird, and the wing of a bat are called
analogous, but not homologous, because their anatomical structure is
different: they are not constructed out of similar anatomical parts.
The fore-leg of a mammal, the wing of a bird, or the paddle of a
whale, are called homologous, because in spite of their diverse uses
they are constructed out of corresponding anatomical parts. To the
anatomist such distinctions are eminently serviceable. But they have
led to some misconceptions, because they are connected with a profound
misconception of the relation between Function and Organ. Embryology
teaches that the wing of the bird and the paddle of the whale are
developed out of corresponding parts, and that these are not like the
parts from which the wing of an insect or the flying-fish will be
developed; nevertheless, the most cursory inspection reveals that the
wing of a bird and the paddle of a whale are very unlike in structure
no less than in function, and that their diversities in function
correspond with their diversities in structure; whereas the wing of the
insect, of the bird, and of the bat, are in certain characters very
similar, and correspondingly there are similarities in their function.
It is, however, obvious that the resemblance in function is strictly
limited to the resemblance in anatomical structure; only in loose
ordinary speech can the flight of an insect, a bird, or a bat be said
to be “the same”: it is different in each--the weight to be moved, the
rapidity of the movement, the precision of the movements, and their
endurance, all differ.
NATURAL SELECTION AND ORGANIC AFFINITY.
118. It is impossible to treat of Evolution without taking notice
of that luminous hypothesis by which Mr. Darwin has revolutionized
Zoölogy. There are two points needful to be clearly apprehended before
the question is entered upon. The first point relates to the lax use
of the phrase “conditions,” sometimes more instructively replaced by
“conditions of existence.” Inasmuch as Life is only possible under
definite relations of the organism and its medium, the “conditions of
existence” will be those physical, chemical, and physiological changes,
which _in_ the organism, and _out_ of it, _co-operate_ to produce the
result. There are myriads of changes in the external medium which have
no corresponding changes in the organism, not being in any direct
relation to it (see § 54). These, not being co-operant conditions,
must be left out of the account; they are not conditions of existence
for the organism, and therefore the organism does not vary with their
variations. On the other hand, what seem very slight changes in the
medium are often responded to by important changes in the vital
chemistry, and consequently in the structure of the organism. Now the
nature of the organism at the time being, that is to say, its structure
and the physico-chemical state of its tissues and plasmodes, is the
main _condition_ of this response; the same external agent will be
powerful, or powerless, over slightly different organisms, or over the
same organism at different times. Usually, and for convenience, when
biologists speak of conditions, they only refer to external changes.
This usage has been the source of no little confusion in discussing
the Development Hypothesis. Mr. Darwin, however, while following the
established usage, is careful in several places to declare that of the
two factors in Variation--the nature of the organism and the nature of
the conditions--the former is by far the more important.
118_a_. A still greater modification of terms must now be made. Instead
of confining the “struggle for existence” to the competition of rivals
and the antagonism of foes, we must extend it to the competition and
antagonism of tissues and organs. The existence of an organism is not
only dependent on the external existence of others, and is the outcome
of a struggle; but also on the internal conditions which co-operate in
the formation of its structure, this structure being the outcome of a
struggle. The organism is this _particular_ organism, differing from
others, because of the particular conditions which have co-operated.
The primary and fundamental struggle must be that of the organic
forces at work in creating a structure capable of pushing its way
amid external forces. The organism must find a footing in the world,
before it can compete with rivals, and defend itself against foes.
Owing to the power of reproduction, every organism has a potential
indefiniteness of multiplication; that potential indefiniteness is,
however, in reality restricted by the supply of food, and by the
competition of rivals for that supply. The multiplication of any one
species is thus kept down by the presence of rivals and foes: a balance
is reached, which permits of the restricted quantities of various
species. This balance is the result of a struggle.
Now let me call attention to a similar process in the formation of the
organism itself. Every organite, and every tissue, has a potential
growth of indefinite extent, but its real growth is rigorously limited
by the competition and antagonism of the others, each of which has
its potential indefiniteness, and its real limits. Something, in the
food assimilated, slightly alters the part which assimilates it. This
change may be the origin of other changes in the part itself, or in
neighboring parts, stimulating or arresting the vital processes. A
modification of structure results. Or there may be no new substance
assimilated, but external forces may call a part into increased
activity--which means increased waste and repair; and this increase
here is the cause of a corresponding decrease somewhere else. Whatever
the nature of the change, it finds its place amid a complex of changes,
and its results are compounded with theirs. When organites and tissues
are said to have a potential indefiniteness of growth, there is
assumed a potential indefiniteness in the pabulum supplied: _if_ the
pabulum were supplied, and _if_ there were no antagonism thwarting its
assimilation, growth would of course continue without pause, or end;
but in reality this cannot be so. For, take the blood as the vehicle
of the pabulum--not only is its quantity limited, and partly limited
by the very action of the tissues it feeds, but even in any given
quantity there is a limit to its composition--it will only take up a
limited quantity of salts, iron, albumen, etc.; no matter how abundant
these may be in the food. So again with the plasmodes of the various
tissues--they have each their definite capacities of assimilation. What
has already been stated respecting chemical affinity (§ 20) is equally
applicable to organic affinity; as the presence of fused iron in the
crucible partially obstructs the combination of sulphur and lead, so
the presence of connective tissue partially obstructs the combination
of muscle protoplasm with its pabulum.
118 _b_. Owing to the action and reaction of blood and plasmode, of
tissues on tissues, and organs on organs, and their mutual limitations,
the growth of each organism has a limit, and the growth of each organ
has a limit. Beyond this limit, no extra supply of food will increase
the size of the organism; no increase of activity will increase the
organ. “Man cannot add a cubit to his stature.” The blacksmith’s arm
will not grow larger by twenty years of daily exercise, after it has
once attained a certain size. Increase of activity caused it to enlarge
up to this limit; but no increase of activity will cause it to pass
this limit. Why? Because here a balance of the co-operating formative
forces has been reached. Larger muscles, or more muscle-fibres, demand
arteries of larger calibre, and these a heart of larger size; with
the increase of muscle would come increase of connective tissue; and
this tissue would not only compete with the muscle for pabulum, but
by mechanical pressure would diminish the flow of that pabulum. And
why would connective tissue increase? Because, in the first place,
there is a formative association between the two, so that owing to a
law, not yet understood, the one always accompanies the other; and,
in the second place, there is a functional association between the
two, a muscle-fibre being _inoperative_ unless it be attached to a
tendon, or connective tissue; it will contract _out_ of the body
although separated from its tendon or other attachment; but _in_ the
body its contraction would be useless without this attachment. We must
bear in mind that muscle-fibres are very much shorter than ordinary
muscles; according to the measurements of W. Krause they never exceed
4 _cm_ in length, and usually range between 2 and 3 _cm_; their fine
points being fixed to the interstitial connective tissue, as the whole
muscle is fixed to its tendon. The function of the muscle is thus
dependent on a due balance of its component tissues; if that balance
is disturbed the function is disturbed. Should, from any cause, an
excess of muscle-fibre arise, the balance would be disturbed; should an
encroachment of connective tissue, or of fat, take place, there would
be also a defect of function.
Here we have the co-operation and limitation of the tissues
illustrated; let us extend our glance, and we shall see how the
co-operation and limitation of the organs come into play, so that
the resulting function depends on the balance of their forces. The
contractile power of each individual muscle is always limited by the
resistance of antagonists, which prevent the muscle being contracted
more than about a third of its _possible_ extent, i. e. possible when
there are no resistances to be overcome. Not only the increasing
tension of antagonist muscles, but the resistance of tendons, bones,
and softer parts must be taken into account. Thus, the increase of
the blacksmith’s muscular power would involve a considerable increase
in all the tissues of the arm; but such an increase would involve a
reconstruction of his whole organism.
Whenever there is an encroachment of one tissue on another, there
is a disturbance of the normal balance, which readily passes into a
pathological state. If the brain is overrun with connective tissue, or
the heart with fatty tissue, we know the consequences. If connective
tissue is deficient, epithelial runs to excess, no longer limited by
its normal antagonist, and pus, or cancer, result.
118_c_. It is unnecessary here to enlarge on this point. I have
adduced it to show that we must extend our conception of the struggle
for existence beyond that of the competition and antagonism of
organisms--the external struggle; and include under it the competition
and antagonism of tissues and organs--the internal struggle.
Variability is inherent in organic substances, as the result of
their indefiniteness of composition (§ 45_b_). This variability is
indefinite, and is rendered definite by the competition and antagonism,
so that every particular variation is the resultant of a composition
of forces. The forces in operation are the internal and external
conditions of existence--i. e. the nature of the organism, and its
response to the actions of its medium. A change may take place in
the medium without a corresponding response from the organism; or the
change may find a response and the organism become modified. Every
modification is a selection, determined by laws of growth; it is the
resultant of a struggle between what, for want of a better term, may
be called the _organic affinities_--which represent in organized
substances what chemical affinities are in the anorganized. Just as
an organism which has been modified and thereby gained a superiority
over others, has by this modification been _selected_ for survival--the
selection being only another aspect of this modification--so one
tissue, or one organ, which has surpassed another in the struggle
of growth, will thereby have become selected. Natural Selection,
or survival of the fittest, therefore, is simply the metaphorical
expression of the fact that any balance of the forces which is best
adapted for survival will survive. Unless we interpret it as a
shorthand expression of _all_ the internal and external conditions of
existence, it is not acceptable as the origin of species.
118_d_. Mr. Darwin has so patiently and profoundly meditated on the
whole subject, that we must be very slow in presuming him to have
overlooked any important point. I know that he has not altogether
overlooked this which we are now considering; but he is so preoccupied
with the tracing out of his splendid discovery in all its bearings,
that he has thrown the emphasis mainly on the external struggle,
neglecting the internal struggle; and has thus in many passages
employed language which implies a radical distinction where--as I
conceive--no such distinction can be recognized. “Natural Selection,”
he says, “depends on the survival under various and complex
circumstances of the best-fitted individuals, but has no relation
whatever to the primary cause of any modification of structure.”[61]
On this we may remark, first, that selection does not _depend_ on
the survival, but _is_ that survival; secondly, that the best-fitted
individual survives because of that modification of its structure
which has given it the superiority; therefore if the primary cause
of this modification is not due to selection, then selection cannot
be the cause of species. He separates Natural Selection from all the
primary causes of variation, either internal or external--either as
results of the laws of growth, of the correlations of variation, of
use and disuse, etc., and limits it to the slow accumulations of such
variations as are profitable in the struggle with competitors. And for
his purpose this separation is necessary. But biological philosophy
must, I think, regard the distinction as artificial, referring only
to one of the great factors in the production of species. And for
this reason: Selection only comes into existence in the modifications
produced either by external or internal changes; and the selected
change cannot be developed further by mere inheritance, unless the
successive progeny have such a disposition of the organic affinities
as will repeat the primary change. Inherited superiority will not by
mere transmission become greater. The facts which are relied on in
support of the idea of “fixity of species” show at any rate that a
given superiority will remain stationary for thousands of years; and
no one supposes that the progeny of an organism will vary unless some
external or internal cause of variation accompanies the inheritance.
Mr. Darwin agrees with Mr. Spencer in admitting the difficulty of
distinguishing between the effects of some definite action of external
conditions, and the accumulation through natural selection of inherited
variations serviceable to the organism. But even in cases where the
distinction could be clearly established, I think we should only see an
_historical_ distinction, that is to say, one between effects produced
by particular causes now in operation, and effects produced by very
complex and obscure causes in operation during ancestral development.
118_e_. The reader will understand that my criticism does not pretend
to invalidate Mr. Darwin’s discovery, but rather to enlarge its
terms, so as to make it include all the biological conditions, and
thus explain many of the variations which Natural Selection--in the
restricted acceptation--leaves out of account. Mr. Darwin draws a broad
line of distinction between Variation and Selection, regarding only
those variations that are favorable as selected. I conceive that all
variations which survive are by that fact of survival, _selections_,
whether favorable or indifferent. A variety is a species in formation;
now Selection itself is not a cause, or condition, of variation, it is
the _expression_ of variation. Mr. Darwin is at times explicit enough
on this head: “It may metaphorically be said that Natural Selection
is daily and hourly scrutinizing throughout the world the slightest
variations; rejecting those that are bad, preserving and adding up
all that are good; silently and insensibly working, whenever and
wherever opportunity offers, at the improvement of each organic being
in relation to its organic and inorganic conditions of life.”[62] But
the metaphorical nature of the term is not always borne in mind, so
that elsewhere Natural Selection is said to “act on and modify organic
beings,” as if it were a positive condition and not the expression
of the modifying processes. Because grouse are largely destroyed by
birds of prey, any change in their color which would render them less
conspicuous would enable more birds to escape; but it is obvious that
this change of color will be due to Organic Affinity; and only when
the change is _effected_ will there have been that selection which
_expresses_ it. Mr. Darwin’s language, however, is misleading. He
says: “Hence Natural Selection might be most effective in _giving_ the
proper color to each kind of grouse, and in _keeping_ that color when
once acquired.” This is to make Selection an agent, a condition of
the development of color; which may be accepted if we extend the term
so as to include the organic changes themselves. Again: “Some writers
have imagined that Natural Selection _induces variability_, whereas it
only implies the _preservation_ of such variations as are beneficial to
the being under its conditions of life.” It, however, is made to imply
more than this, namely, the accumulation and further modification of
such variations. “The mere existence of individual variability and of
some well-marked varieties, though necessary as the foundation, helps
us but little in understanding how species arise in nature. How have
all those exquisite adaptations of one part of the organization to
another part, and to the conditions of life, and of one organic being
to another being, been perfected?” My answer to this question would
be: By Organic Affinity, and the resulting struggle of the tissues and
organs, the consequences of which are that very _adaptation_ of the
organism to external conditions, which is expressed as the _selection_
of the structures best adapted. The selections are the results of the
struggle, according to my proposed extension of the term “struggle.”
Mr. Darwin defines the struggle: “The dependence of one being on
another, and including (what is more important) not only the life of
the individual but success in leaving progeny.” This definition seems
defective, since it omits the primary and more important struggle
which takes place between the organic affinities in operation. To
succeed in the struggle with competitors, the organism must have first
acquired--by selection--a superiority in one or more of its organs.
118_f_. A little reflection will disclose the importance of keeping
our eyes fixed on the internal causes of variation, as well as on the
external conditions of the struggle. Mr. Darwin seems to imply that the
external conditions which cause a variation are to be distinguished
from the conditions which accumulate and perfect such variation, that
is to say, he implies a radical difference between the process of
variation and the process of selection. This, I have already said, does
not seem to me acceptable; the selection, I conceive, to be simply the
variation which has survived.[63]
If it be true that a Variety is an incipient Species and shows
us Species in formation, it is in the same sense true that a
variation is an incipient organ. A species is the result of a slowly
accumulating divergence of structure; an organ is the result of a
slowly accumulating differentiation. At each stage of differentiation
there has been a selection, but we cannot by any means say that this
selection was determined by the fact of its giving the organism a
superiority over rivals, inasmuch as during all the early stages,
while the organ was still in formation, there could be no advantage
accruing from it. One animal having teeth and claws developed will
have a decided superiority in the struggle over another animal that
has no teeth and claws; but so long as the teeth and claws are in an
undeveloped state of mere preparation they confer no superiority.
118_g_. Natural Selection is only the expression of the results of
obscure physiological processes; and for a satisfactory theory of such
results we must understand the nature of the processes. In other words,
to understand Natural Selection we must recognize not only the facts
thus expressed, but the factors of these facts,--we must analyze the
“conditions of existence.” As a preliminary analysis we find _external
conditions_, among which are included not only the dependence of the
organism on the inorganic medium, but also the dependence of one
organism on another,--the competition and antagonism of the whole
organic world; and _internal conditions_, among which are included not
only the dependence of the organism on the laws of composition and
decomposition whereby each organite and each tissue is formed, but also
the dependence of one organite and one tissue on all the others--the
competition and antagonism of all the elements.
The changes wrought in an organism by these two kinds of conditions
determine Varieties and Species. Although many of the changes are due
to the process of natural selection brought about in the struggle
with competitors and foes, many other changes have no such relation
to the external struggle, but are simply the results of the organic
affinities. They may or they may not give the organism a greater
stability, or a greater advantage over rivals; it is enough that they
are no disadvantage to the organism, they will then survive by virtue
of the forces which produced them.
119. The position thus reached will be important in our examination
of the Theory of Descent by which Mr. Darwin tentatively, and his
followers boldly, explain the observed resemblances in structure and
function as due to blood-relationship. The doctrine of Evolution
affirms that all complex organisms are evolved by differentiation from
simpler organisms, as we see the complex organ evolved from simpler
forms. But it does not necessarily affirm that the vast variety of
organisms had one starting-point--one ancestor; on the contrary, I
conceive that the principles of Evolution are adverse to such a view,
and insist rather on the necessity of innumerable starting-points. Let
us consider the question.
That the Theory of Descent explains many of the facts must be admitted;
but there are many which it leaves obscure; and Mr. Darwin, with
that noble calmness which distinguishes him, admits the numerous
difficulties. Whether these will hereafter be cleared away by an
improvement in the Geological Record, now confessedly imperfect, or
by more exhaustive exploration of distant countries, none can say;
but, to my mind, the probability is, that we shall have to seek our
explanation by enlarging the idea of Natural Selection, subordinating
it to the laws of Organic Affinity. It does not seem to me, at present,
warrantable to assume Descent as the sole principle of morphological
uniformities; there are other grounds of resemblance beyond those of
blood-relationship; and these have been too much overlooked; yet a
brief consideration will disclose that similarity in the physiological
laws and the conditions of Organic Affinity must produce similarity
in organisms, independently of relationship; just as similarity in
the laws and conditions of inorganic affinity will produce identity
in chemical species. We do not suppose the carbonates and phosphates
found in various parts of the globe, or the families of alkaloids and
salts, to have any nearer kinship than that which consists in the
similarity of their elements and the conditions of their combination.
Hence, in organisms, as in salts, morphological identity may be due
to a community of conditions, rather than community of descent. Mr.
Darwin justly holds it to be “incredible that individuals identically
the same should have been produced through Natural Selection from
parents _specifically distinct_,” but he, since he admits analogous
variations, will not deny that identical forms might issue from parents
having widely different origins, provided that these parent forms
and the conditions of their reproduction were identical, as in the
case of vegetable and animal resemblances. To deny this would be to
deny the law of causation. And that which is true of identical forms
under identical conditions is true of similar forms under similar
conditions. When History and Ethnology reveal a striking uniformity in
the progression of social phases, we do not thence conclude that the
nations are directly related, or that the social forms have a common
parentage; we conclude that the social phases are alike because they
have had common causes. When chemists point out the uniformity of type
which exists in compounds so diverse in many of their properties as
water and sulphuretted or selenetted hydrogen, and when they declare
phosphoretted hydrogen to be the congener of ammonia, they do not mean
that the one is descended from the other, or that any closer link
connects them than that of resemblance in their elements.
In the case of vegetal and animal organisms, we observe such a
community of elementary substance as of itself to imply a community in
their laws of combination; and under similar conditions the evolved
forms must be similar. With this community of elementary substance,
there are also diversities of substance and of co-operant conditions;
corresponding with these diversities there must be differences of
form. Thus, although observation reveals that the bond of kinship does
really unite many widely divergent forms, and the principle of Descent
with Natural Selection will account for many of the resemblances and
differences, there is at present no warrant for assuming that all
resemblances and differences are due to this one cause, but, on the
contrary, we are justified in assuming a deeper principle which may be
thus formulated: All the complex organisms are evolved from organisms
less complex, as these were evolved from simpler forms; the link which
unites all organisms is not always the common bond of heritage, but the
uniformity of organized substance acting under similar conditions.
It is therefore consistent with the hypothesis of Evolution to admit a
variety of origins or starting-points, though not consistent to admit
the sudden appearance of complex Types, such as is implied in the
hypothesis of specific creations.
119 _a_. The analogies of organic forms and functions demand a more
exhaustive scrutiny than has yet been given them. Why is it that
vessels, nerves, and bones _ramify_ like branches, and why do these
branches take on the aspect of many crystalline forms? Why is it that
cavities are constantly prolonged in ducts, e. g. the mouth succeeded
by the œsophagus, the stomach by the intestines, the bladder by the
urethra, the heart by the aorta, the ovary by the oviduct, and so
on? Why are there never more than four limbs attached to a vertebral
column, and these always attached to particular vertebræ? Why is
there a tendency in certain tissues to form tubes, and in these tubes
commonly to assume a muscular coat?[64] To some of these queries an
answer might be suggested which would bring them under known physical
laws. I merely notice them here for the sake of emphasizing the fact
that such analogies lie deeply imbedded in the laws of evolution, and
that what has been metaphorically called organic crystallization will
account for many similarities in form, without forcing us to have
recourse to kinship. To take a very simple case. No one will maintain
that the crystalline forms of snow have any kinship with the plants
which they often resemble. Mr. Spencer has noticed the development
of a wing-bearing branch from a wing of the _Ptilota plumosa_, when
its nutrition is in excess. “This form, so strikingly like that of the
feathery crystallizations of many inorganic substances, proves to us
that in such crystallizations the simplicity or complexity of structure
at any place depends on the quantity of matter that has to be polarized
at that place in a given time. How the element of time modifies the
result, is shown by the familiar fact that crystals rapidly formed
are small, and that they become larger when they are formed more
slowly.”[65]
It may be objected, and justly, that in the resemblance between
crystals and organisms the analogy is purely that of form, and usually
confined to one element, whereas between organisms there is resemblance
of substance no less than of form, and usually the organisms are alike
in several respects. The answer to this objection is, that wherever
there is a similarity in the causal conditions (substance and history)
there must be a corresponding similarity in the results; if this
similarity extends to only a few of the conditions, the analogy will
be slight; if to several, deep. But whether slight or deep we are not
justified, simply on the ground of resemblance, in assuming, short of
evidence, that because they are alike, two organisms are related by
descent from a common ancestor.
120. Let us glance at a few illustrations. It has been urged as a
serious objection to Mr. Darwin’s hypothesis,[66] that it fails to
explain the existence of phosphorescent organs in a few insects; and
certainly, when one considers the widely different orders in which
these organs appear, and their absence in nearly related forms, it
is a difficulty. In noctilucæ, earthworms, molluscs, scolopendra,
and fireflies, we may easily suppose the presence of similar organic
conditions producing the luminosity; but it requires a strong faith to
assign Descent as the cause.[67] We may say the same of the electric
organs possessed by seven species of fish, belonging to five widely
separated genera. Although each species appears to have a limited
geographical range, one or the other is found in almost every part
of the globe. These organs occupy different positions, being now on
each side of the head, now along the body, and now along the tail;
and in different species they are innervated from different sources.
Their intimate structure also varies; as appears from the remarkable
investigations of Max Schultze.[68] They cannot, therefore, be
homologous. How could they have arisen? Not by the slow accumulations
of Natural Selection, because, until the organs were fully formed, they
could be of no advantage in the struggle; hence the slow growth of
the organ must have proceeded without the aid of an advantage in the
struggle--in each case from some analogous conditions which produced
a differentiation in certain muscles. The fundamental resemblance to
muscles was pointed out by Carus long ago. It has been insisted on by
Leydig:[69] and Owen says, “The row of compressed cells constituting
the electric prism of the Torpedo offers some analogy to the row of
microscopic discs of which the elementary muscle fibre appears to
consist.”[70] We must not, however, forget that these resemblances are
merely such as suggest that the electric organ is a _differentiation_
of the substance which elsewhere becomes muscular, and that Dr.
Davy was justified in denying the organ to be muscular.[71] That it
is substituted for muscle cannot be doubted. Now, although we are
entirely ignorant of the conditions which cause this differentiation of
substance which elsewhere becomes muscular, but here becomes electric
organs, we can understand that, when once such a development had
taken place, if it in any way profited the fish in its struggle for
existence, Natural Selection would _tend_ to its further increase and
propagation. So far Mr. Darwin carries us with him; but we decline
proceeding further. The development of these organs in fishes so widely
removed, does not imply an ancestral community. It is interpretable as
mere growth on a basis once laid; and therefore would occur with or
without any advantage in the struggle with rivals. The similarity in
concurrent conditions is quite enough to account for the resemblance
in structure. This, with his accustomed candor, Mr. Darwin admits. “If
the electric organs,” he says, “had been inherited from one ancient
progenitor thus provided, we might have expected that all electric
fishes would be specially related to each other. Nor does Geology at
all lead to the belief that formerly most fishes had electric organs
which most of their modified descendants have lost.”
121. It may seem strange that he should urge a difficulty against
his hypothesis when it could be avoided by the simple admission that
even among nearly allied animals great differences in development
are observable, and the electric organs might be ranged under such
diversities. But Mr. Darwin has so thoroughly wrought out his scheme,
that he foresees most objections, and rightly suspects that if this
principle of divergent development be admitted, it will cut the ground
from under a vast array of facts which his hypothesis of Descent
requires.
The sudden appearance of new organs, not a trace of which is
discernible in the embryo or adult form of organisms lower in the
scale,--for instance, the phosphorescent and electric organs,--is
like the sudden appearance of new instruments in the social organism,
such as the printing-press and the railway, wholly inexplicable
on the theory of Descent,[72] but is explicable on the theory of
Organic Affinity. For observe: if we admit that differentiations
of structure, and the sudden appearance of organs, can have arisen
spontaneously--i. e. not hereditarily--as the outcome of certain
changed physical conditions, we can hardly refuse to extend to the
whole organism what we admit of a particular organ. If, again, we
admit that organs very similar in structure and function spontaneously
appear in organisms of widely different kinds--e. g. the phosphorescent
and electric organs--we must also admit that similar resemblances may
present themselves in organisms having a widely different parentage;
and thus the admission of the spontaneous evolution of closely
resembling organs carries with it the admission of the spontaneous
evolution of closely resembling organisms: that the protoplasm of
muscular tissue should, under certain changed conditions, develop
into the tissue of electric organs, is but one case of the law that
organized substance will develop into organisms closely resembling each
other when the conditions have been similar.
122. It is to be remarked that Mr. Darwin fixes his attention somewhat
too exclusively on the adaptations which arise during the external
struggle for existence, and to that extent neglects the laws of organic
affinity; just as Lamarck too exclusively fixed his attention on the
influence of external conditions and of wants. Not that Mr. Darwin can
be said to overlook the organic laws; he simply underestimates the part
they play. Occasionally he seems arrested by them, as when instancing
the “trailing palm in the Malay Archipelago, which climbs the loftiest
trees by the aid of exquisitely constructed hooks, clustered around
the ends of the branches, and this contrivance no doubt is of the
highest service to the plant; but as there are nearly similar hooks
on many trees which are not climbers, the hooks on the palm may have
arisen from unknown laws of growth, and have been subsequently taken
advantage of by the plant undergoing further modification and becoming
a climber.”
123. I come round to the position from which I started, that the
resemblances traceable among animals are no proof of kinship; even a
resemblance so close as to defy discrimination would not, in itself,
be such a proof. The absolute identity of chalk in Australia and in
Europe is a proof that there was absolute identity in the formative
conditions and the constituent elements, but no proof whatever that the
two substances were originally connected by genesis. In like manner
the similarity of a plant or animal in Africa and Europe may be due
to a common kinship, but it may also be due to a _common history_. It
is indeed barely conceivable that the history, from first to last,
would ever be so rigorously identical in two parts of the globe as
to produce complex identical forms in both; because _any_ diversity,
either in structure or external conditions, may be the starting-point
of a wide diversity in subsequent development; and the case of organic
combinations is so far unlike the inorganic, that while only one form
is possible to the latter (chalk is either formed or not formed), many
forms are possible to organic elements owing to the complexity and
indefiniteness of organic composition. But although forms so allied as
those of Species are not readily assignable to an identical history
in different quarters of the globe, it is not only conceivable, but
is eminently probable, that Orders and Classes have no nearer link of
relationship than is implied in their community of organized substance
and their common history. The fact that there is not a single mammal
common to Europe and Australia is explicable, as Mr. Darwin explains
it, on the ground that migration has been impossible to them; but it
is also explicable on the laws of Evolution--to have had mammals of
the same species and genera would imply a minute coincidence in their
history, which is against the probabilities. Again, in the Oceanic
Islands there are no Batrachians; but there are Reptiles, and these
conform to the reptilian type. Mr. Darwin suggests that the absence of
Batrachia is due to the impossibility of migration, their ova being
destroyed by salt water. But may it not be due to the divergence
from the reptilian type, which was effected elsewhere, not having
taken place in these regions? When we find the metal Tin in Prussia
and Cornwall, and nowhere else in Europe, must we not conclude that
in these two countries, and nowhere else, a peculiar conjunction of
conditions caused this peculiar evolution?
124. The question at issue is, Are the resemblances observable
among organic forms due to remote kinship, and their diversities
to the divergences caused by adaptation to new conditions? or
are the resemblances due to similarities, and the diversities to
dissimilarities in the _substance and history_ of organic beings?
Are we to assume one starting-point and one centre of creation, or
many similar starting-points at many centres? So far from believing
that all plants and animals had their origin in one primordial cell,
at one particular spot, from which descendants migrated and became
diversified under the diverse conditions of their migration, it seems
to me more consistent with the principle of Evolution to admit a vast
variety of origins more or less resembling each other; and this initial
resemblance will account for the similarities still traceable under
the various forms; while the _early differences_, becoming intensified
by development under different conditions, will yield the diversities.
The evolution of organisms, like the evolution of crystals, or the
evolution of islands and continents, is determined, 1st, by laws
_inherent in the substances evolved_, and, 2d, by relations to the
medium in which the evolution takes place. This being so, we may
_à priori_ affirm that the resultant forms will have a community
strictly corresponding with the resemblance of the substances and
their conditions of evolution, together with a diversity corresponding
with their differences in substance and conditions. It is usually
supposed that the admission of separate “centres of creation” is
tantamount to an admission of “successive creations” as interpreted by
the majority of those who invoke “creative fiats.” But the doctrine
of Evolution, which regards Life as making its appearance _consequent
upon a concurrence of definite conditions_, and regards the specific
forms of Life as the necessary consequences of special circumstances,
must also accept the probability of similar conditions occurring at
different times and in different places. Upon what grounds, cosmical
or biological, are we to assume that on only _one_ microscopic spot of
this developing planet such a group of conditions was found--on only
one spot a particle of protein substance was formed out of the abundant
elements, and under conditions which caused it to grow and multiply,
till in time its descendants overran the globe? The hypothesis that
all organic forms are the descendants of a single germ, or of even
a few germs, and are therefore united by links of kinship more or
less remote, is not more acceptable than the hypothesis that all
the carbonates and phosphates, all the crystals, and all the strata
found in different parts of the globe, are the _descendants of a
single molecule_, or a few molecules; or,--since this may seem too
extravagant,--than that the various maladies which afflict organic
beings are, in a literal sense, members of _families_ having a nearer
relationship than that of being the phenomena manifested by similar
organs under similar conditions--a conception which might have been
accepted by those metaphysical pathologists who regarded Disease as
an entity. Few philosophers have any hesitation in supposing that
other planets besides our own are peopled with organic forms, though,
from the great differences in the conditions, these forms must be
extremely unlike those of our own planet. If separate worlds, why not
separate centres? The conclusion seems inevitable that wherever and
whenever the state of things permitted that peculiar combination of
elements known as organized substance, there and then a centre was
established--Life had a root. From roots closely resembling each other
in all essential characters, but all more or less different, there have
been developed the various stems of the great tree. Myriads of roots
have probably perished without issue; myriads have developed into forms
so ill-adapted to sustain the fluctuations of the medium, so ill-fitted
for the struggle of existence, that they became extinct before even our
organic record begins; myriads have become extinct since then; and the
descendants of those which now survive are like the shattered regiments
and companies after some terrific battle.
125. There seems to me only one alternative logically permissible to
the Evolution Hypothesis, namely, that all organic forms have had
either a single origin, or else numerous origins; in other words, that
a primordial cell was the starting-point from which all organisms
have been successively developed; or that the development issued
from many independent starting-points, more or less varied. This is
apparently not the aspect presented by the hypothesis to many of its
advocates; they seem to consider that if all organic forms are not the
lineal descendants of one progenitor, they must at any rate be the
descendants of not more than four or five. The common belief inclines
to one. Mr. Darwin, whose caution is as remarkable as his courage, and
whose candor is delightful, hesitates as to which conclusion should
be adopted: “I cannot doubt,” he says, “that the theory of descent,
with modifications, embraces all the members of the same class. I
believe that animals have descended from, at most, only four or five
progenitors, and plants from an equal or lesser number. Analogy would
lead me one step further, namely, to the belief that all animals and
plants have descended from some one prototype. But analogy may be a
deceitful guide.”
126. I cannot see the evidence which would warrant the belief that Life
originated solely in one microscopic lump of protoplasm on one single
point of our earth’s surface; on the contrary, it is more probable that
from innumerable and separate points of this teeming earth, myriads
of protoplast sprang into existence, _whenever_ and _wherever_ the
conditions of the formation of organized substance were present. It is
probable that this has been incessantly going on, and that every day
new protoplasts appear, struggle for existence, and serve as food for
more highly organized rivals; but whether an evolution of the lower
forms is, or is not, still going on, there can be no reluctance on
the part of every believer in Evolution to admit that when organized
substance was first evolved, it was evolved at many points. If this be
so, the community observable in organized substance, wherever found,
may as often be due to the fact of a common elementary composition as
to the fact of inheritance. If this be so, we have a simple explanation
both of the fundamental resemblances which link all organisms together,
and of the characteristic diversities which separate them into
kingdoms, classes, and orders. The resemblances are many, and close,
because the forms evolved had a similar elementary composition, and
their stages of evolution were determined by similar conditions.
The diversities are many, because the forms evolved had from the
first some diversities in elementary composition, and their stages of
evolution were determined under conditions which, though similar in
general, have varied in particulars. Indeed, there is no other ground
for the resemblances and differences among organic beings than the
similarities and dissimilarities in their Substance and History; and,
whether the similarities are due to blood-relationship, or to other
causes, the results are the same. There is something seductive in the
supposition that Life radiated from a single centre in ever-increasing
circles, its forms becoming more and more various as they came under
more various conditions, until at last the whole earth was crowded
with diversified existences. “From one cell to myriads of complex
organisms, through countless æons of development,” is a formula of
speculative grandeur, but I cannot bring myself to accept it; and I
think that a lingering influence of the tradition of a “creative fiat”
may be traced in its conception. May we not rather assume that the
earth at the dawn of Life was a vast germinal membrane, every slightly
diversified point producing its own vital form; and these myriads upon
myriads of forms--all alike and all unlike--urged by the indwelling
tendencies of development, struggled with each other for existence,
many failing, many victorious, the victors carrying their tents into
the camping ground of the vanquished. The point raised is the immense
improbability of organized substance having been evolved only in one
microscopic spot; if it were evolved at more than one spot, and under
slightly varying conditions, there would necessarily have arisen in
these earliest formations the _initial_ diversities which afterwards
determined the essential independence and difference of organisms.
129. Let us for a moment glance at the resemblances and diversities
observable in all organisms. All have a _common basis_, all being
constructed out of the same fundamental elements: carbon, hydrogen,
nitrogen, and oxygen; these (the organogens, as they are named),
with varying additions of some other elements, make up what we know
as Organic Substance, vegetal and animal. Another peculiarity all
organisms have in common, namely, that their matter is neither solid
nor liquid, but viscid. Beside this community of _Substance_ we must
now place a community of _History_. All organisms grow and multiply by
the same process; all pass through metamorphic stages ending in death;
all, except the very simplest, differentiate parts of their substance
for special uses, and these parts (cilia, membranes, tubes, glands,
muscles, nerves) have similar characters in whatever organism they
appear, and their development is always similar, so that the muscles or
nerves of an intestinal worm, a lobster, or a man, are in structure and
history fundamentally alike. When, therefore, we see that there is no
biological character of fundamental importance which is not universal
throughout the organic world, when we see that in Structure and History
all organisms have a community pervading every variety, it is difficult
not to draw the conclusion that some hidden link connects all organisms
into one; and when, further, it is seen that the most divergent forms
may be so arranged by the help of intermediate forms only slightly
varying one from the other, that the extreme ends--the monad and the
man--may be connected, and a genealogical tree constructed, which
will group all forms as modified descendants from a single form, the
hypothesis that kinship is the bidden link of which we are in search
becomes more and more cogent.
130. But now let the other aspect be considered. If there is
an unmistakable uniformity, there is also a diversity no less
unmistakable. The chemical composition of organic substances is
various. Unlike inorganic substances, the composition of which is
rigorously definite, organic substances are, within narrow limits,
variable in composition (§ 45).
I pass over the resemblances and differences observed in the earliest
stages of development, marked as they are, and direct attention to the
fact, that down at what must be considered the very lowest organic
region, we meet with differences not less striking than those met with
in the highest, we find structures (if structures they may be called),
which cannot be affiliated, so widely divergent is their composition.
The structureless vibrio, for example, is not only capable of living
in a medium destitute of Oxygen, but is, according to M. Pasteur,
actually killed by oxygen; whereas the equally simple bacteria can
no more dispense with Oxygen than other animals can. Consider for a
moment the differences implied in the fact that one organism cannot
even form an enveloping membrane to contain its protoplasm, whereas
another contrives to secrete an exquisite shell; yet between the
naked Rhizopod and the shelled Rhizopod our lenses and reagents fail
to detect a difference. One Monad can assimilate food of only one
kind, another Monad assimilates various kinds.[73] What a revelation
of chemical differences appears in the observations of M. Pasteur
respecting the vibrio and bacteria, in a fermentescible liquid--the
former beginning the putrid fermentation which the latter completes!
We cannot doubt that some marked difference must exist between the
single-celled organism which produces alcoholic fermentation, and that
which produces acetic fermentation, and that again which produces
butyric fermentation; and if we find distinctions thus established
at the lowest region of the organic series, we need not marvel if
the distinctions become wider and more numerous as the series becomes
more diversified. The structure and development of an organism are
dependent on the affinities of its constituent molecules, and it is
a biological principle of great importance which Sir James Paget
insists on, when he shows how “the existence of certain materials
in the blood may determine the formation of structures in which
they may be incorporated.”[74] _Any_ initial diversity may thus
become the starting-point of a considerable variation in subsequent
evolution.[75] Thus, supposing that on a given spot there are a dozen
protoplasts closely resembling each other, yet each in some one detail
slightly varying; if this variation is one which, by its relations to
the external medium, admits of a difference in the assimilation of
materials present in the medium, it may be the origin of some _new
direction_ in development, and the ultimate consequence may be the
formation of a shell, an internal skeleton, a muscle, or a nerve.
Were this not so, it would be impossible to explain such facts as
that chitine is peculiar to the Articulata, cellulose to Molluscoida,
carbonates of lime to Mollusca and Crustacea, and phosphates to
Vertebrata--all assimilated from the same external medium. But we
see that from this medium one organism selects the materials which
another rejects; and this selection is determined by the nature of the
structure: which assimilates only those materials it is _fitted_ to
assimilate. We hear a great deal of Adaptation determining changes of
structure and function, and are too apt to regard this process as if it
were not intimately dependent on a corresponding structural change. By
no amount of external influence which left the elementary composition
of the structure unchanged, could an organism with only two tissues
be developed into an organism with three or four. By no supply or
stimulus, could an animal incapable of assimilating peroxide of iron
acquire red blood corpuscles, although it might have the iron without
the corpuscles; nor could an oyster form its shell unless capable of
assimilating carbonate of lime. For myriads of years, in seas and
ponds, under endless varieties of external conditions, the amœbæ have
lived and died without forming a solid envelope, although the materials
were abundant, and other organisms equally simple have formed envelopes
of infinite variety. In all the seas, and from the earliest ages,
zoophytes have lived, and assumed a marvellous variety of shapes and
specialization of functions; but although some of them have acquired
muscles, none have acquired true nerves, none bone. Ages upon ages
rolled on before fishes were capable of forming bone; and thousands are
still incapable of forming it, though living in the same waters as the
osseous fishes.
131. “Looking to the dawn of life,” says Mr. Darwin (repeating an
objection urged against his hypothesis), “when all organic beings, as
we imagine, presented the simplest structure, how could the first steps
in advancement, or in the differentiation and specialization of parts
have arisen? I can make no sufficient answer; and can only say that,
as we have no facts to guide us, all speculation would be baseless and
useless.”
Where Mr. Darwin hesitates, lesser men need extra caution; but I
must risk the danger of presumption, at least so far as to suggest
that while an answer to this question is difficult on that dynamical
view of Evolution which regards Function as determining Structure,
it is less difficult on the statico-dynamical view propounded in
these pages; the difficulty which besets the explanation when all the
manifold varieties of organic forms are conceived as the successive
divergences from an original starting-point, is lessened when a variety
of different starting-points is assumed, in each of which some initial
diversity prepared the way for subsequent differentiations; just as
we know that between the ovum of a vertebrate and the ovum of an
invertebrate, similar as they are, there is a diversity which manifests
itself in their subsequent evolution. If Function is determined by
Structure, and Evolution is the product of the two, it is clear that
the different directions in the lines of development will have their
origin in structural differences, and not in the action of external
circumstances, unless these previously bring about a structural change.
The action of the medium on the organism is assuredly a potent factor
which Biology cannot ignore: but the organism itself is a factor, and
according to its nature the influence of the medium is defined. (§ 118.)
132. Quitting for a moment the track of this argument, let us glance
at the resemblances and differences observable in Plants and Animals,
because most people admit that these have separate origins. The
resemblances are scarcely less significant than those existing among
animals. Both have a similar basis of elementary composition; not only
are both formed out of protoplasts with similar properties, but in both
the first step from the protoplasm to definite structure is the Cell.
And the life of this Cell is remarkably alike in both, its phases of
development being in many respects identical; nay, even such variations
as obtain in the cell-membranes are curiously linked together by a
community in the formative process.[76] In both Plants and Animals
we find individuals constituted--1st, by single cells; 2d, by groups
of cells undistinguishable among each other; and 3d, by groups of
differentiated cells. In both we find colonies of individuals leading
a common life. In both the processes of Nutrition and Reproduction
are essentially similar; both propagate sexually and asexually; both
exhibit the surprising phenomena of parthenogenesis and alternate
generations. In both there are examples of a free-roving embryo which
in maturity becomes fixed to one spot, losing its locomotive organs
and developing its reproductive organs. In both the development of the
reproductive organs is the climax which carries Death. So close is the
analogy between plant-life and animal-life, that it even reaches the
properties usually held to be exclusively animal; I mean that even
should we hesitate to accept Cohn’s discovery of the muscles in certain
plants,[77] we cannot deny that plants exhibit Contractility; and
should we refuse to interpret as Sensibility the phenomena exhibited by
the Sensitive Plants, we cannot deny that they present a very striking
analogy to the phenomena of Sensibility exhibited by animals.
133. It is unnecessary to continue this enumeration, which might easily
be carried into minute detail. A chapter of such resemblances would
only burden the reader’s mind, without adding force to the conclusion
that a surprising community in Substance and Life-history must be
admitted between Plants and Animals. This granted, we turn to the
differences, and find them no less fundamental and detailed. Chemistry
tells us nothing of the differences in the protoplasms from which
animals and plants arise; but that initial differences must exist is
proved by the divergence of the products. The vegetable cell is not
the animal cell; and although both plants and animals have albumen,
fibrine, and caseine, the _derivatives_ of these are unlike. Horny
substance, connective tissue, nerve tissue, chitine, biliverdine,
creatine, urea, hippuric acid, and a variety of other products of
evolution or of waste, never appear in plants; while the hydrocarbons
so abundant in plants are, with two or three exceptions, absent from
animals. Such facts imply differences in elementary composition; and
this result is further enforced by the fact that where the two seem
to resemble, they are still different: the plant protoplasm forms
various cells, but never forms a cartilage-cell or nerve-cell; fibres,
but never a fibre of elastic tissue; tubes, but never a nerve tube;
vessels, but never a vessel with muscular coatings; solid “skeletons,”
but always from an organic substance (_cellulose_), not from phosphates
and carbonates. In no one character can we say that the plant and the
animal are identical; we can only point throughout the two kingdoms to
a great similarity accompanying a radical diversity.
134. Having brought together the manifold resemblances, and the no
less marked diversities, we must ask what is their significance? Do
the resemblances imply a community of origin, an universal kinship?
If so, the diversities will be nothing more than the divergences
which have been produced by variations in the Life-history of the
several groups. Or--taking the alternative view--do the diversities
imply radical differences of origin? If so, the resemblances will be
nothing more than the inevitable analogies resulting from Organized
Substance being everywhere somewhat similar in composition, and similar
in certain phases of evolution. To state the former position in the
simplest way, we may assume that of two masses of protoplasm having
a common parentage, one, by the accident of assimilating a certain
element not brought within the range of the other, thereby becomes so
differentiated as to form the starting-point of a series of evolutions
widely divergent from those possible to its congener; and at each stage
of evolution the introduction of a new element (made possible by that
stage) will form the origin of a new variation. It is thus feasible to
reduce all organic forms to a primordial protoplasm, in the evolutions
of which successive differentiations have been established. On the
other hand, it is equally feasible to assume that the existence of
radical differences must be invoked to account for the possibility of
the successive differentiations.
135. The hunt after resemblances has led to much mistaken speculation;
and with reference to the topic now before us, it may be urged,
that although by attaching ourselves to the points of community, in
disregard of the diversities, we may make it appear that all animals
have a common parentage, and that plants and animals are merely
divergent groups of the same prototype, a rigorous logic will force us
onwards, and compel us to admit that a kinship no less real unites
the organic with the inorganic world. For upon what principle are we
to pause at the cell or protoplasm? If by a successive elimination
of differences we reduce all organisms to the cell, we must go on
and reduce the cell itself to the chemical elements out of which it
is constructed; and inasmuch as these elements are all common to the
inorganic world, the only difference being one of synthesis, we reach a
result which is the stultification of all classification, namely, the
assertion of a kinship which is universal. We must bear in mind that
all things may be reduced to a common root by simply disregarding their
differences. All things are alike when we set aside their unlikeness.
136. Suppose, for the sake of illustration, we regard an Orchestra
in the light of the Development Hypothesis. The various instruments
of which it is composed have general resemblances and particular
differences, not unlike those observable in various organisms; and
as we proceed in the work of classification we quickly discover that
they may be arranged in groups analogous to the Sub-kingdoms, Classes,
Orders, Genera, and Species of the organic world. Each group has its
cardinal distinction, its initial point of divergence. All musical
instruments resemble each other in the fundamental character of
producing Tone by the vibrations of their substance. This may be called
their organic basis. The first marked difference which determines the
character of two sub-kingdoms (namely, instruments of Percussion and
Wind instruments) arises from a difference in the method of impressing
the vibrations; and the grand divisions of these sub-kingdoms arise
from the nature of the vibrating substances. Each type admits of many
modifications, but the primary distinction is ineffaceable. We can
conceive the Pipe modified into a Flute, a Flageolet, a Clarionet,
a Hautbois, a Bassoon, or a Fife, by simple accessory changes; to
modify the Pipe into a Trumpet, and thus produce the peculiar _timbre_
of the trumpet, would be impossible except by the _substitution_
of a new material; by replacing the wood with metal we may adhere
to the old Type, but we have created a new Class. (Attention is
requested to this point, because the current views respecting the
transmutation of tissues, which seem to lend a decisive support to the
hypothesis of the transmutation of species are very commonly vitiated
by the confusion of transformation with substitution. No anatomical
element is _transformed_ into another specifically different--an
epithelial-cell into a nerve-cell, for instance--but one anatomical
element is frequently _substituted_ for another.) To convert the Pipe
or the Trumpet into a Violin or a Drum would be impossible. We can
follow the modifications of a Tambourine into a Drum or Kettle-drum,
but no modifications of these will yield the Cymbals. That is to say,
the vibrating materials--wood, metal, parchment, and the combination
of wood and strings--have peculiar properties, and the instruments
formed of such materials must necessarily from the very first belong
to different groups, each subdivision of the groups being dependent on
some characteristic difference in methods of impressing the vibrations,
or in the materials. Although all musical instruments have a common
property and a common purpose, we do not regard them as transformations
of one primitive instrument; their kindred nature is a subjective
conception; the analogies are numerous and close, but we know their
origin. It is obvious that men being pleased by musical tones, have
been led by their delight to construct instruments whenever they have
discovered substances capable of musical vibrations, or methods of
impressing such vibrations. By substituting the bow for the plectrum or
the fingers, they may have changed the Lyre into the Violin, Viola,
Violoncello, and Bass. (It seems historically probable that the real
origin of the Violin class was an instrument with one string played on
by a bow.) By grouping together Pipes of various sizes they got the
Panpipes; by substituting metal and enlarging the blowing apparatus
they got the Organ. By beating on stretched parchment with the finger,
they got the Tambourine and Tom-Tom; by doubling this and using a stick
they got the Drum. By beating metal with metal they got the Cymbals; by
beating wood they got the Castanets.
137. The application of this illustration is plain. Just as a
wind-instrument is incapable of becoming a stringed instrument, so
a Mollusc, with all its muscles unstriped, and its nervous system
unsymmetrical, is incapable of becoming a Crustacean, with all its
muscles striped and its nervous system symmetrical. Indeed there
are probably few biologists of the present day who imagine the
transmutation of one kind into the other to be possible; but many
biologists assume that both may have been evolved from a common root.
The point is beyond proof; yet I think there is a greater probability
in the assumption that both were evolved from different roots. At any
rate, one thing is certain; a divergence could only have been effected
by a series of _substitutions_; and the question when and how these
substitutions took place is unanswerable: one school believes them to
have been creative fiats, the other school believes them to have been
transmutations.
138. When we see an annelid and a vertebrate resembling each other in
some special point which is not common either to their classes or to
any intermediate classes--as when we see the wood-louse (_Oniscus_)
and the hedgehog defend themselves in the same strange way by rolling
up into a ball--we cannot interpret this as a trace of distant
kinship. When we see a breed of pigeons and a breed of canaries
turning somersaults, and one of the Bear family (_Ratel_) given to the
same singular habit, we can hardly suppose that this is in each case
inherited from a common progenitor. When we see one savage race tipping
arrows with iron, and another, ignorant of iron, using poison, there is
a community of object effected by diversity of means; but the analogy
does not necessarily imply any closer connection between the two races
than the fact that men with similar faculties and similar wants find
out similar methods of supplying their wants. Even those who admit that
the human race is one family, and that the various peoples carried with
them a common fund of knowledge when they separated from the parent
stock, may still point to a variety of new inventions and new social
developments which occurred quite independently of each other, yet are
strikingly alike. Their resemblance will be due to resemblance in the
conditions. The existence, for example, of a religious worship, or a
social institution, in two nations widely separated both in time and
space, and under great historical diversities, is no absolute proof
that these two nations are from the same stock, and that the ideas have
the same parentage. It may be so; it may be otherwise. It may be an
analogy no more implying kinship than the fact of ants making slaves
of other ants (and these the black ants!) implies a kinship with men.
Given an organization which in the two nations is alike, and a history
which is in certain characteristics analogous, there must inevitably
result religious and social institutions having a corresponding
resemblance. I do not wish to imply that the researches of philologists
and ethnologists are misdirected, or that their conclusions
respecting the kinship of mankind are to be rejected; I only urge the
consideration that perhaps too much stress is laid on community of
blood, and not enough on community of conditions.
RECAPITULATION.
139. The various lines of argument may here be recapitulated. The
organic world presents a spectacle of endless diversity, accompanied by
a pervading uniformity. The general resemblances in forms and functions
are more or less masked by particular differences. The resemblances, it
is said, may be all due to kinship, all the living individuals having
descended from a primordial cell; and at each stage of the descent the
adaptations to new conditions may have issued in deviations from the
ancestral form, while the process of Natural Selection giving stability
to those variations which best fitted the organism in the struggle of
existence, has made greater and greater gaps, and produced more marked
diversities among the descendants. This is the Darwinian Theory: “On my
theory unity of Type is explained by unity of Descent.”
140. By the general consent of biologists, this theory is held to
explain many if not all the observed facts. It is a very luminous
suggestion; but it requires an enlargement so as to include Organic
Affinity; and when once this fundamental principle is admitted, it
brings with it very serious doubts as to the theory of Descent.
We are then entitled to assume that many of the most striking
resemblances, instead of being due to kinship, are due simply to the
general principle that similar causes must have similar effects, and
that organic substances having a very close resemblance, organized
substances must have similar stages of evolution under similar
conditions; and thus organs will necessarily take on very similar forms
in very different organisms (for example, the eye of the cephalopod
and the eye of the vertebrate), and organisms having widely different
parentage may closely resemble each other. If we are entitled to
assume that protoplasm appeared not in one microscopic spot alone, but
in many places and in vast quantities--and this is surely the more
justifiable assumption--then we must also admit that these germinal
starting-points were from the first, or very shortly afterwards,
differentiated by variations in their elementary composition. Now we
know that a very minute change in composition may lead to immense
differences in evolution. Thus the descendants of two slightly
different progenitors may, by continual differentiation, become very
markedly unlike; yet, because of the original resemblance of their
substances, they will reveal a pervading similarity.
While it is thus conceivable that all organisms may resemble each
other, and all differ, owing to the similarities and diversities in the
“conditions of existence” (and among those conditions that of descent
is of wide range), it is not very readily conceivable how advantage
in the external struggle could have determined the varieties of form
and function, because many differentiations give no superiority in the
struggle. As Mr. St. George Mivart urges, “Natural Selection utterly
fails to account for the conservation and development of the minute and
rudimentary beginnings, the slight and infinitesimal commencements of
structures, however useful those structures may afterwards become.”[78]
And this is undeniable on the supposition that Natural Selection is an
agency not identical with the variations of growth, but exclusively
confined to the accumulation of favorable variations.
141. In estimating the two hypotheses--First, of Descent from one
primordial germ, and the modifications _due_ to Natural Selection, or,
as I should say, _expressed_ in Selection; and Secondly, of Descent
from innumerable germs having initial differences, which differences
radiated into the marked modifications, there is this superiority to
be claimed for the first, that it is more easily handled as an aid to
research, and is therefore more decidedly useful. The laws of Organic
Affinity are at present too obscure for any successful application.
I only wish to point out that the theory of Descent is an imaginary
construction of what _may have been_ the process of species-formation,
not a transcription of the process observed. It constructs an imaginary
Type as progenitor of a long line of widely different descendants. The
annelid which is taken as the ancestor of the vertebrates is not any
annelid known either to zoölogists or geologists, but a generalized
and imaginary type. So daringly liberal is the imagination in endowing
the ancestor with whatever may be required for the descendants, that
Mr. Darwin thinks it _probable_, from what we know of the embryos
of vertebrates, that these animals “are the modified descendants
of some ancient progenitor which was furnished in its adult state
with branchiæ, a swim-bladder, four simple limbs, and a long tail,
all fitted for an organic life,” (p. 533); and Dr. Dohrn conceives
the original type to have contained within itself all that has been
subsequently evolved in the highest vertebrate, the other and less
elaborate organisms being mere degradations from this type.[79] This
use of the imagination, although not without advantages, is also not
without dangers. It may direct research, it must not be suffered to
replace research.
PROBLEM II.
THE NERVOUS MECHANISM.
“All the functions of the nervous system are as dependent upon its
structure and nature, as the accurate indication of time upon the
construction of the chronometer.”--PROCHASKA.
“Unser Wissen wird nie vollendet, ist und bleibt Stückwerk; dessen
Ergänzung das Streben und Hoffen der forschenden Denker bleiben
wird für alle Zeit.”--RADENHAUSEN, _Osiris_.
“Our nimble souls
Can spin an insubstantial universe
Suiting our mood, and call it possible,
Sooner than see one grain with eye exact,
And give strict record of it.”
GEORGE ELIOT, _The Spanish Gypsy_.
“If we compare the teachings of our books with what Nature is
constantly showing, we find there is no agreement between those two
sources of learning.”--BROWN SÉQUARD.
THE NERVOUS MECHANISM.
CHAPTER I.
SURVEY OF THE SYSTEM.
1. Our knowledge of mental processes is derived from reflection on our
personal experiences, combined with inferences from our observation
of other men and animals, under similar conditions. The processes
are complex and variable; so complex and variable, that knowledge of
their component factors can only be gained through long tentative
study, aided by fortunate circumstances which present these factors
separately, or at any rate in such marked predominance as to fix
attention. This subjective analysis of the _processes_ has to be
supplemented by, and confirmed by an objective analysis of, the
_conditions_, external and internal: the facts of Feeling have to be
traced to facts of Physiology, which will exhibit that Physical Basis
of Mind so earnestly sought by the inquirer.
Both the subjective and the objective analysis are at present in a
very imperfect state. Although there is much confident assertion and
“false persuasion of knowledge” in both regions, there is, unhappily,
little that can be seriously accepted as demonstrated. In the present
volume we shall concern ourselves almost exclusively with the objective
analysis, and do our utmost to mark what is mere inference from what
is verified observation. It is only by Observation that facts can be
_settled_; however Analogy and Inference may suggest where the truth
may lie, they are finger-posts, not goals. At the best they only tell
us what Observation _would_ reveal could the processes be submitted to
Sense.
In a loose and general way every one knows that the Nervous System is
a dominant agent in all sentient processes; although not by any means
the only agent, yet, because of its predominance, it is artificially
accepted as the only one. With the greater complexity of this system,
there is observed a corresponding increase in the variety of sentient
phenomena. The labors of anatomists have secured a tolerably exact plan
of the topographical distribution of this system; a somewhat chaotic
mass of observation and inference passes as a description of its
elementary structure. The labors of physiologists have succeeded to a
small extent in localizing certain functions in certain organs of this
system. But imperfect as our knowledge of the elementary structures is,
our knowledge of the functions is still more so. I wish I could say
otherwise, and that I could ask my readers to accept with confidence
what teachers confidently propound. The attitude of scepticism is
always repulsive; the sceptic is seldom received without disfavor,
because he throws on us the labor of investigation there where we wish
for the confidence of knowledge. Yet it is only by facing the facts
that we can hope one day to solve the great questions.
2. The nervous system has, in our artificial view of it, two divisions:
the Peripheral, which connects the organism with the external world;
and the Central, which connects each part of the organism with all
the other parts. Although the system is constituted by various
tissues--neural, connective, vascular, and elastic--it receives its
characteristic designation from nerve-fibrils, nerve-fibres, and
nerve-cells; just as the muscular system receives its designation
from contractile cells and fibres. This neural tissue assumes three
well-marked forms: 1°, _nerves_, which are bundles of fibres and
fibrils, enclosed in a membranous sheath; 2°, _ganglia_, which are
clusters of cells, fibres, and fibrils, sometimes enclosed in a sheath,
sometimes not; 3°, _centres_, which are artificial divisions of the
neural axis, serving as points of union for different organs.
In the Invertebrata the neural axis is the chain of ganglionic masses
running along the ventral side, and giving off the nerves to organs of
sense, and to the muscles. It may be seen represented in Fig. 1.
[Illustration: Fig. 1.--_Nervous system of a beetle._ The small round
masses, or _ganglia_, are seen to be connected by longitudinal fibres,
and from the ganglia issue fibres to the limbs, organs of sense, and
viscera.]
In the Vertebrata the axis is dorsal, and is called the _cerebro-spinal
axis_, including brain and spinal cord. When we look at this structure
superficially we see various nerves radiating _from_ it to skin,
glands, and muscles; but a closer examination, enlightened by knowledge
of function, shows that some of these nerves pass _into_ it from the
various surfaces and sense-organs, and are therefore called _afferent_
or _sensory_; whereas another set passes out of it to glands and
muscles, and these nerves are therefore called _efferent_ or _motory_.
There are also fibres which, passing from one part of the great centre
to another, are called _commissural_.
To this brief account of the cerebro-spinal system may be added a word
on the connected chain of ganglia and nerves known as the Sympathetic,
because it was formerly supposed to be the organ through which the
various “sympathies” were effected. It is now held to be the system
devoted to the viscera and blood-vessels; but there is still great want
of agreement among physiologists as to whether it is an independent
system, having a special structure somewhat different from that of the
cerebro-spinal, or whether it is simply a great plexus of nerves and
ganglia, only topographically distinguishable from the rest of the
nervous system. Into this point it is unnecessary for me to enter here.
Enough to say, that I entirely agree with Sigmund Mayer in adopting
the second view.[80] In no histological character, yet specified, are
the sympathetic nerves and ganglia demarcated from the others. There
are, indeed, _more_ non-medullary fibres (the gray fibres of Remak)
in the sympathetic; but the same fibres are also abundant in the
cerebro-spinal system; and the sympathetic has also its large medullary
fibres.
3. The Centres are composed of two substances: the gray and the white.
The gray substance is often called the vesicular because of its
abundant cells; but it has even more fibres than cells, and the white
substance has also a few cells.[81] The gray substance is distributed
over the surface of the brain--in the convolutions; and in various
other parts of the encephalon. It surrounds the central canal which
forms the ventricles of the brain and is continued as a very small
cavity all down the spinal cord. Besides entering into the important
and conspicuous masses known as the cerebral ganglia--(the _optic
thalami_, and _corpora striata_)--the gray substance is massed in the
_corpora quadrigemina_, _crura cerebri pons varolii_, and _medulla
oblongata_. We shall have occasion to refer to each of those parts.
Until modern times all the masses included in the skull under the
familiar term Brain (or the technical term Encephalon) were regarded
as the only centre, and also as the origin of all the nerves. Nor has
this notion even yet entirely disappeared, although the spinal cord
is known not to be a large nerve trunk, but a centre or connected
chain of centres, structurally and functionally similar to the cranial
centres. The shadow of the ancient error still obscures interpretation
of the part this spinal cord plays in the sentient mechanism; and thus
although the cord is universally admitted to be a centre for “sensitive
impressions,” it is usually excluded from Sensation. This widespread
and misleading notion will be critically examined in a future problem.
4. Beginning our survey of the cerebro-spinal axis with the Spinal
Cord, we observe it to consist: 1°, of _central gray substance_
surrounding the scarcely visible canal, which is all that remains of
the primitive groove in the germinal membrane (§ 9); 2°, irregular
gray masses, called the _anterior and posterior horns_,[82] connected
with the anterior and posterior _roots_ of the spinal nerves; and 3°,
strands of white fibres enclosing this central substance, and called
the _anterior lateral and posterior columns_.
Like the Cerebrum, it is a double organ formed by two symmetrical
halves, as the cerebrum is of two hemispheres. Each half innervates
the corresponding half of the body. The cord is unlike the cerebrum
in external form, though very like it in internal structure. The gray
structure is mainly external in the cerebrum, and is internal in the
cord.
From the anterior side of the cord (that which in animals is the under
side) the motor nerves issue; from the posterior (in animals the
upper) side, issue the sensory nerves. On each of the sensory nerves
there is a ganglion. The _roots_ of each nerve, formed of several
rootlets issuing from the anterior and posterior columns, subsequently
unite together, and proceed in a single sheath to muscles and skin,
separating again, however, before they reach muscles and skin. Fig. 2
represents this arrangement.
[Illustration: Fig. 2.--_A portion of the spinal cord with its nerves_
(after Bernard). The left-hand figure shows the anterior side; the
right-hand the posterior. A the anterior, and P, the posterior root,
they meet at _g_, the ganglion; _c_ and _d_ are filaments connecting
two posterior roots.]
5. There are thirty-one pairs (sometimes thirty-two) of such
nerves--namely, eight cervical, twelve thoracic, five lumbar, five
sacral, and one (or two) coccygeal. Figs. 3 to 6 represent transverse
sections, which display the entrance of the roots of the nerves into
the anterior and posterior horns.
6. Similar masses of gray substance in the _Medulla Oblongata_ (which
is the name given to the cord when it passes into the skull)[83] are
supposed to be the origins of some other nerves (the cranial).
[Illustration: Fig. 3.--_Transverse section of one half of the
spinal cord in the lumbar region_ (after Kölliker). _a_, anterior
root entering the anterior gray horns, _m_ and _l_, where cells are
clustered; _c_, central canal; _d_ and _e_, the anterior and posterior
commissures uniting the two halves of the cord; _b_, posterior root
entering the posterior gray horn.]
[Illustration: Fig. 4.--_Transverse section of both halves of the cord,
cervical region._ _a_, Fissure separating the anterior columns; _b_,
fissure of the posterior.]
[Illustration: Fig. 5.--_Transverse section of the cord in the dorsal
region._]
[Illustration: Fig. 6.--_Transverse section in the lumbar region._]
Although the Medulla Spinalis is unquestionably continued as the
Medulla Oblongata, the arrangement of its tissues here becomes
gradually changed, and so complicated that it baffles the scalpel.
Anatomists are, however, agreed on the one point of fundamental
importance to us here--namely, that there is only a rearrangement, not
a new tissue. Accepting the artificial division into two organs, we may
say that their functions are different, inasmuch as they are different
in their anatomical connections--they innervate different parts; but as
nerve-centres they have one and the same property.
On its posterior surface the Medulla Oblongata opens as the _fourth
ventricle_. It is then no longer a closed canal, but an expansion of
the spinal canal, which is covered by the Cerebellum. On its anterior
surface projects the _pons varolii_. Figs. 7 and 8 represent these.
[Illustration:
Fig. 7.--_Back, or upper view of the Medulla Oblongata as it
continues the Med. Spinalis._ 1, Section of the thalami; 2, corpora
quadrigemina (the two lower bodies are imperfectly represented in
the engraving); 3, section of the crura cerebelli; 4, the fourth
ventricle; 5, the restiform bodies; 6, the calamus scriptorius.
]
[Illustration:
Fig. 8.--_Front, or under view of the Med. Oblong._ 1, Optic nerves
cut off at the chiasma; 2, crura cerebri; 3, pons varolii; 4,
olivary bodies; 5, anterior pyramids; 6, spinal columns.
]
While thus on the one hand continuing the Medulla Spinalis, the
Medulla Oblongata is seen on the other hand to be continuous with the
Brain--its white columns passing upwards in the _crura cerebri_, its
cavity repeated in the other ventricles. Above it lie the ganglionic
masses, the _corpora quadrigemina_, _optic thalami_, and _corpora
striata_. Crowning these are the big and little brains, Cerebrum and
Cerebellum. Figs. 9 and 10 represent this relation of Medulla Spinalis,
Medulla Oblongata, and Brain. Fig. 11 is a purely artificial diagram
which will give the reader some idea of the disposition of the white
and gray substances.
[Illustration:
Fig. 9.--_Human Brain in Profile._ 1, Cerebrum; 2, cerebellum; 3,
pons varolii and medulla oblongata.
]
[Illustration:
Fig. 10.--_One half of the Brain in Profile, from the inside._
1, Convolutions of the cerebrum; 2, corpus callosum or great
commissure uniting the two hemispheres; 3, arbor vitæ or branching
arrangement of gray and white matter in the cerebellum; 4, pons
varolii and medulla.
]
[Illustration:
Fig. 11.--_Diagram of a vertical section of the Brain_ (after
Dalton). 1, Olfactory ganglion; 2, cerebral hemisphere; 3, corpus
striatum; 4, thalamus; 5, corpora quadrigemina; 6, cerebellum; 7,
ganglion of the pons varolii; 8, olivary body.
]
7. In man the Cerebrum is to the Cerebellum as 9 to 1. In the lower
vertebrates the preponderance is still greater. The cerebrum is in our
artificial systems commonly divided into three lobes. The frontal lobe
is that portion which lies in front of the deep fissure named after
Rolando; between that fissure and the “internal perpendicular fissure”
lies the parietal lobe; behind this we have the occipital lobe; and,
below the fissure of Sylvius, the tempero-sphenoidal lobe. Each lobe is
again subdivided according to its convolutions.
The disposition of the fibres in the brain is far too complex to be
accurately followed. All that we can say is, that there are strands
which connect one convolution with another, strands which connect
one hemisphere with another, strands which connect cerebrum with
cerebellum, and strands which connect the cerebrum with the lower
ganglia. It is important to conceive this distinctly; for we shall
hereafter see that the function of the Brain (by brain is here meant
both Cerebrum and Cerebellum) is not that of _innervation_, but of
_incitation and regulation_. To speak metaphorically, it is the
coachman who holds in his hands the reins, and guides the team. One
cardinal fact should arrest attention, namely, that not a single nerve
in the body has its origin or centre of innervation in the cerebrum and
cerebellum. The olfactory and optic nerves do indeed _seem_ to issue
from the cerebrum; and are commonly described as cerebral nerves. But
the facts of Development, minute Anatomy, and Experiment prove this to
be inexact. Although I shall continue to speak of the olfactory and
optic nerves in accordance with universal usage, not wishing to burden
the reader with unnecessary innovations, I must at the outset express
my opinion that these nerves cannot be brought under the same general
type as the other sensory nerves. Embryology and Anatomy suggest that
they have no more claim to the title than the _crura cerebri_. Of this
hereafter. Setting these aside, no one now refuses to acknowledge
that Cerebrum and Cerebellum, although centres of Incitation and
Association, are not the centres of direct Innervation: the organic
mechanism in all its _physiological_ processes will act independently
of them (so far as such artificial distinctions are admissible at all).
This does not throw a doubt on their _physiological_ functions, nor on
their participation in the normal execution of physiological processes.
8. From this rapid survey two important points may be selected for
special attention. First, the continuity of the neural axis throughout;
secondly, the fundamental similarity of its _structure_, underlying
great variations in its form and connections. This, which is the
anatomical expression of the Unity of the nervous system, will become
more evident after we have expounded what Embryology and Microscopic
Anatomy teach. We may therefore digress here awhile to consider
THE EARLY FORMS OF NERVE CENTRES.
9. In the outermost layer of the germinal membrane of the embryo a
groove appears, which deepens as its sides grow upwards, and finally
close over and form a canal. This canal is composed of cells all alike.
Its foremost extremity soon bulges into three well-marked enlargements,
which are then called the _primitive cerebral vesicles_. The cavities
of these vesicles are continuous. Except in position and size, there
are no discernible differences in these vesicles, which are known as
the Fore-brain, Middle-brain, and Hind-brain.
10. The _Fore-brain_ soon buds off from each side a small vesicle. This
is the optic vesicle, the first rudiment of what subsequently becomes
optic nerve and retina. At this period it is simply a vesicle with
a hollow stem, the cavity being continuous with the cavity of the
cerebral vesicle, and the walls continuous with the cerebral wall.
It thus appears that the retina and optic “nerve” are primitive
portions of the brain--a detached segment of the general centre,
identical in structure with the cerebral vesicle, and not unlike in
form. A cup-like depression quickly forms the optic vesicle into an
inner and an outer fold. The inner or concave fold becomes the retina,
and the outer or convex fold (that nearest to the brain) becomes its
choroid membrane. On the fourth day of incubation the retina of the
chick is composed of spindle-shaped cells, all alike. On the seventh
day there is a differentiation into layers, one of which on the eighth
day is granular; on the tenth two are granular; and on the thirteenth
ganglionic cells appear. Some of the cells have elongated into radial
fibres (known as Müller’s fibres); and with the appearance of rods and
cones the normal retinal elements are complete.
11. The researches of Foster and Balfour[84] confirm the statement that
all the different parts of the retina (whether nervous or connective)
are derived from one and the same layer of embryonic cells, which
originally formed a portion of the first cerebral vesicle.
12. Meanwhile the hollow stem of this optic vesicle begins to develop
fibres amidst the nuclei of its walls. The “optic nerve” arises: it
is still hollow; and in birds remains so through life. The fibres as
they are developed _grow forwards towards the retina_, and spread over
its internal surface. _They also grow forwards towards the brain_,
and spread over its substance; but it is _not_, as might be supposed,
and is generally believed, with the cerebral hemispheres (or that
portion of the Fore-brain from which these are derived), but with the
Middle-brain (which becomes the _corpora quadrigemina_), that the optic
fibres are in connection.[85]
13. This will be understood when the further development is traced.
The Fore-brain, after budding off the optic vesicles, buds off two
larger vesicles--the future cerebral hemispheres. This is noticeable
on the second day of incubation, and by the third day each vesicle is
as large as the whole of the original Fore-brain. Their development is
essentially like that of the optic vesicles; both as to the cellular
and the fibrous elements.
The _convolutions_, _corpus callosum_, _nucleus lentiformis_,
and _corpora striata_ are then indicated. Meanwhile, that which
originally was the Fore-brain has lapsed into the secondary rank as
Intermediate-brain (_Zwischenhirn_), and becomes the parts surrounding
the third ventricle, namely, the _thalami_, _corpora candicantia_,
_infundibulum_, and what is called the “posterior perforated substance.”
14. The _Middle-brain_, or Second Vesicle, develops the _corpora
quadrigemina_ from the roof of its cavity, and the _crura cerebri_ from
its floor.
The _Hind-brain_, or Third Vesicle, divides into two, like the First
Vesicle; it buds off the hemispheres of the cerebellum; its cavity
forms the fourth ventricle; its walls the _medulla oblongata_.
15. It thus appears that the primitive membrane forms into a canal,
which enlarges at one part into three vesicles, and from these are
developed the encephalic structures. The continuity of the walls
and cavities of these vesicles is never obliterated throughout the
subsequent changes. It is also traceable throughout the medulla
spinalis. And microscopic investigation reveals that underneath all the
morphological changes the walls of the whole cerebro-spinal axis are
composed of similar elements on a similar plan.[86]
16. Two conclusions directly follow from this exposition:--first, that
_since the structure of the great axis is everywhere similar, the
properties must be similar_; secondly, that _since there is structural
continuity, no one part can be called into activity without at the same
time more or less exciting that of all the rest_.
THE PERIPHERAL SYSTEM.
17. Following the analytical division, we now come to the Peripheral
System of nerves and ganglia. The separation, I must often repeat,
is purely artificial; but the artifice has conveniences. We separate
in the same way the heart from veins and arteries, and the capillary
circulation from the arterial.
Each nerve has its direct connection with a particular centre, and
indirectly with the whole system. It has its circumscribed territory,
and individual office. Except in a few cases of anastomosis, the action
of one nerve does not involve that of another: only one muscle or one
group of muscles is moved, without exciting motion in a neighbor. It is
through the centres that these individual territories are united; and
a wave of excitation always passes throughout the central substance.
Thus the centres are not simply organs of association, consequently of
regulation, but are the nexus whereby the diversity of the actions is
integrated into the unity of consensus.
18. Nothing further need at present be stated respecting the nerves;
but it is needful to give precision to the ideas of
GANGLIA AND CENTRES,
usually spoken of as if they were convertible terms. That this is
inexact may be readily shown, and that it is misleading appears in its
causing physiologists to credit every ganglion, wherever found, with
central functions; and, by an almost inevitable extension of the error,
has led to the assignment of central functions to a single ganglionic
cell! This is but part of that “superstition of the cell” against
which I shall have to protest. I will not here raise the doubt which
presses from various sides respecting the central functions of the
ganglia in the heart and intestines, because the reader perhaps shares
the general opinion on that point; but let me simply ask what central
function can possibly be assigned to the ganglia on each of the spinal
sensory nerves? above all to those grouped and scattered ganglionic
cells which are found at the peripheral termination of some nerves, and
in the very trunks of others? There may, indeed, be imagined a central
function for the ganglia in the mesentery, and even in the choroid coat
of the retina, on the hypothesis (quite gratuitous, I think) of their
regulating the circulation; but even this explanation cannot be adopted
with respect to the ganglionic cells which appear in the course of the
nerve.[87]
The meaning of a physiological centre is, that it is a point _to_ which
stimulations proceed, and _from_ which they are reflected. The meaning
of a ganglion is, that it is a group of nerve cells dispersed among, or
in continuation with, nerve fibres: it may be a centre of reflection,
or it may not; and in the latter case its physiological office is at
present undetermined. A ganglion is no more a centre in virtue of its
cell-group than a muscle is a limb. All function depends on connection,
and central function demands a connection of afferent and efferent
parts.
19. The ganglia found in the ventral cord of the Invertebrate (see
Fig. 1) are centres, each of which has considerable independence,
each regulating a single segment of the body, or a group of similar
segments. As the scale of animal complexity ascends, these separated
centres tend more and more to coalesce, and with this coalescence
comes an increasing _combination_ of movements.[88] Observe the
caterpillar slowly crawling over a leaf; each segment of its body moves
in succession; but when this caterpillar becomes a butterfly the body
moves rapidly, and all at once. Open the caterpillar, and you find its
nervous centres are thirteen separate ganglia, each presiding over a
distinct part of the body, and each capable of independent action.
Open the butterfly, and you find the thirteen ganglia greatly changed:
the second and third are fused into one; the fourth, fifth, and sixth
into another; the eleventh and twelfth into another; the only trace of
the original separation is in a slight constriction of the surface. The
movements of the caterpillar were few, simple, slow, and those of the
butterfly are many, varied, and rapid.
20. In the Vertebrates the coalescence of ganglia is such that the
spinal axis is one great centre. We do indeed anatomically and
physiologically subdivide it into several centres, because several
portions directly innervate separate organs; but its importance lies in
the intimate blending of all parts, so that _fluctuating combinations_
of its elements may arise, and varied movements result. Each centre
combines various muscles; the axis is a combination of centres. The
brainless frog, for instance, has still the spinal cord, and therefore
the power not only of moving either of his limbs, but also of combining
their separate movements: if grasped, he struggles and escapes; if
pricked, he hops away. But these actions, although complex, are much
less complex and varied than the actions of the normal frog.
There is not only a coalescence of ganglia, but a greater and greater
concentration of the substance in the upper portions of the axis. In
the inferior vertebrates, and in the mammalian embryo, the spinal
cord occupies the whole length of the vertebral canal from the head
to the tip of the tail; and here the centres of reflexion correspond
with the several segments. But as the cranial mass develops there is a
withdrawal of neural substance from the lower parts, and the centres of
reflexion are then some way removed from the segments they innervate.
In the animal development there is even a greater and greater
predominance of the upper portions, so that the brain and medulla
oblongata are of infinitely more importance than the spinal cord.
21. Besides the central group of elements which belong to fixed and
definite actions, we must conceive these elements capable of variable
combinations, like the pieces of colored glass in a kaleidoscope, which
fall into new groups, each group having its definite though temporary
form. The elements constitute really a continuous network of variable
forms. It is to such combinations, and not to fixed circumscribed
ganglia, that we must refer the subordinate centres of the axis. We
speak of a centre for Respiration, a centre for Laughing, a centre for
Crying, a centre for Coughing, and so on, with as much propriety as
we speak of a centre for Swallowing or for Walking. Not that in these
cases there is a circumscribed mass of central substance set apart for
the innervation of the several muscles employed in these actions, and
for no other purpose. Each action demands a definite group of neural
elements, as each geometric form in the kaleidoscope demands a definite
group of pieces of glass; but these same pieces of glass will readily
enter into other combinations; and in like manner the muscles active
in Respiration are also active in Laughing, Coughing, etc., though
differently innervated and co-ordinated.
22. The physiological rank of a centre is therefore the expression of
its power of fluctuating combination. The medulla oblongata is higher
than the medulla spinalis, because of its more varied combinations;
the cerebrum is higher than all, because it has no fixed and limited
combinations. It is the centre of centres, and as such the supreme
organ.
CHAPTER II.
THE FUNCTIONAL RELATIONS OF THE NERVOUS SYSTEM.
23. The distinguishable parts of this system are the central axis, the
cranial nerves, and the spinal nerves, with the chain of ganglia and
nerves composing the Sympathetic. Let us briefly set down what is known
of their special offices.
Men very early discovered that the nerves were in some way ministrant
to Sensation and Movement; a divided nerve always being accompanied
by insensibility and immobility in the limb. Galen, observing that
paralysis of movement sometimes occurred without insensibility,
suggested that there were two kinds of nerve; but no one was able to
furnish satisfactory evidence in support of this suggestion until early
in the present century, when the experiments of Charles Bell, perfected
by those of Majendie and Müller, placed the suggestion beyond dispute.
[Illustration: Fig. 12.--_Transverse sections of spinal cord (dorsal
region)._]
24. Fig. 12 is a _diagram_ (not a drawing of the actual aspect, which
would be hardly intelligible to readers unversed in such matters)
representing two transverse sections of the spinal cord just where the
nerve-roots issue. The gray substance is somewhat in the form of a
rude H, in the dorsal region, and of the expanded wings of a butterfly
in the lumbar enlargements (Figs. 4–6); the extremities of this gray
substance are the _anterior and posterior horns_. We have already said
that from the anterior horns of each half issue the roots of the motor
nerves, which pass to the muscles. From the posterior horns issue the
sensory nerves, which, soon after leaving the cord, enter the ganglia
before joining the motor nerves, and then pass to the skin, in the
same sheath with their companions, separating again as they reach the
muscles and surfaces where they are to be distributed. When this mixed
nerve is cut through, or tied, all sensation and movement disappear
from the parts innervated. But if only one of the roots be cut through,
above the ganglion, there will then be only a loss of movement or a
loss of sensation. Thus suppose the section be made at _a_, _b_, A:
we have then divided a sensory nerve, and no pinching or pricking of
the part innervated by that nerve will be felt; but movement will take
place if the under nerve be irritated, or if a sensation _elsewhere_ be
excited. Now reverse the experiment, as at B, _c_, _d_. Then, pricking
of the skin will be felt, but no movement will respond. The nerve which
enters the cord at the upper (posterior) part is therefore a sensory
nerve; that which enters at the under (anterior) part is motor. The
direction is in each case indicated by the arrow. The central end _b_,
if irritated, will produce sensation; whereas the peripheral end _a_
produces neither sensation nor movement. The central end _d_ produces
neither sensation nor movement; the peripheral end _c_ produces
movement.
25. Two facts are proved by these experiments. First, that the
co-operation of the centre is necessary for Sensation, but not for
Movement. Although normally all the muscles of the trunk are moved only
when their centre has been excited, yet any irritation applied directly
to the muscle nerve, even when separated from its centre, produces a
movement. And to this we may add that a slighter stimulus will move the
muscle by direct irritation of the nerve, than by indirect irritation
through the centre; a slighter stimulus also will suffice when applied
to the nerve than when applied to the muscle itself.
26. The second fact proved is known as _Bell’s Law_, that the sensory
and motor channels are respectively the posterior and anterior nerves.
The fact is indisputable, but its theoretic interpretation can no
longer be accepted in its original form. Bell supposed the two nerves
to be different in kind, endowed with different specific energies, the
one sensitive, the other motor. The majority of writers still express
themselves as if they adopted this view. We shall, however, presently
see reason for replacing it by the more consistent interpretation
which assigns one and the same property to both nerves, marking their
distinction by the terms afferent and efferent; the one set being
anatomically so disposed that it conveys stimuli from the surfaces to
the centre, and the other set conveying stimuli from the centre to the
muscles, glands, and other cells.[89]
27. Bell’s discovery was rapidly generalized. The principle of
localization was extended to all nerves, and of course to the posterior
and anterior columns of the spinal cord, which indeed were assumed to
be continuations of the nerves. Bell, who was greater as an anatomist
than as a philosopher, always maintained that anatomical deduction was
superior to experiment. But this was to misunderstand the reach of
deduction, which is only valid to the extent of its premises.[90] In
the present case, the premises assumed that the posterior columns were
continuations of the posterior roots, and carried impressions to the
brain, the anterior columns carrying back from the brain the “mandates
of the will.” Experiment has, however, decisively shown that it is
_not_ through the posterior columns that sensory impressions travel to
the brain, but through the central gray substance.
28. The spinal cord with its central gray substance is at each point
a centre of reflexion. Connected as it is with different organs, we
artificially consider it as a chain of different centres, and try to
detect the functional relations of its parts. The inquiry is important,
but we must bear in mind the cardinal principle that diversity of
Function depends on the organs innervated, and not on a diversity of
Property in the nervous tissue. Although all nerves have a common
structure and common property, yet we distinguish them as sensory and
motor; and the sensory we subdivide into those of Special Sensation
and those of Systemic Sensation. The motor we divide into muscular,
vasomotor, and glandular. The hypothesis of specific energies must be
relinquished (§ 63).
In like manner all centres have a common structure and a common
property, with a great diversity of functional relations. Here also the
hypothesis of specific energies has been generally adopted, owing to
a mistaken conception of the biological principle just mentioned. The
cerebral hemispheres are credited with the properties of sensation,
thought, and volition; the cerebellum with the property of muscular
co-ordination; the spinal cord with the property of reflexion.
29. No attempt to assign the true functional relations of the centres
will be made at the present stage of our exposition. We must learn more
of the processes in Sensation, Thought, and Volition, before we can
unravel the complex physiological web on which they depend. But here,
provisionally, may be set down what observation and experiment have
disclosed respecting the part played by certain centres. We know, for
example, that when the cerebral hemispheres are carefully removed from
a reptile or a bird, all the essentially _vital_ functions go on pretty
much as before, but a great disturbance in some of the _psychical_
functions is observed. The brainless bird eats, drinks, sleeps, moves
its limbs separately and in combination, manifests sensibility to
light, sound, and touch, performs such instinctive actions as preening
its feathers, or thrusting the head under the wing while roosting.
Throw it into the air and it will fly. In its flight it will avoid
obstacles, and will alight upon a ledge, or your shoulder. But it will
not fly unless thrown into the air; it will not escape through the
open door or window; it will avoid objects, but will show no fear of
them,--alighting on your head, for example, without hesitation. It is
sensitive to light, and may in a certain sense be said to _see_; but
it fails to _perceive_ what is _seen_. It will eat and drink, if food
and water be administered, but it will starve near a heap of grain and
never peck it, not even if the beak be thrust into the heap. A grain,
or strip of meat, may be thrust inside the beak; there it will remain
unswallowed, unless it touches the back of the mouth, then swallowing
at once follows the stimulus. The bird _with_ its brain will fly away
if you turn the finger, or stick, on which it is perching; _without_
its brain, it makes no attempt to fly, but flutters its wings, and
balances itself. If you open the mouth of a cat, or rabbit, and drop
in some bitter fluid, the animal closes its mouth firmly, and resists
your efforts to repeat the act; without its brain, the animal shows the
same disgust at the taste, but never resists the preliminaries of the
repetition.
30. These, and analogous facts, have been noted by various
experimenters. They are very far from proving what is usually
concluded; but they prove the important negative position that the
cerebrum is not the centre of innervation for any of the organs on
which the observed actions depend. Thus, the cerebrum is not necessary
to sight: _ergo_ it does not innervate the eye. It is not necessary to
hearing: _ergo_ it does not innervate the ear.[91] It is not necessary
to breathing, swallowing, flying, etc.: _ergo_ it does not innervate
the organs of these functions.
What then is lost? We have only to remember that the cerebrum is
continuous with the thalami and corpora striata, and, through its
crura, with the medulla oblongata and medulla spinalis, to foresee
that its removal must more or less affect the whole neural axis,
and consequently disturb the actions of the whole organism; this
disturbance will often have the appearances which would be due to the
removal of a central apparatus, so that we shall be apt to attribute
the cessation of a function to the loss of its organ, when in fact the
cessation is due simply to an arrest of the organ by irritation. Thus
the cessation of consciousness, or of any particular movements, when
the cerebrum is removed, is no decisive proof that the cerebrum is the
organ of consciousness, or of the movement in question. This point will
be duly considered hereafter. What we have now to consider is the facts
observed after removal of the cerebrum.
First, we observe a loss of that power of combining present states
with past states, present feelings with feelings formerly excited in
conjunction with them, the power which enables the animal to adjust
its actions to certain sensations _now unfelt_ but which _will be_
felt in consequence of the adjustment. Secondly, we observe a loss of
Spontaneity: the bird, naturally mobile and alert, now sits moveless
for hours in a sort of stupor, occasionally preening its feathers, but
rarely quitting its resting-place. All the most conspicuous phenomena
which we assign to Intelligence and Will seem absent. The sensations
are altered and diminished. Many Instincts have disappeared, but some
remain. The sexual feeling is preserved, although the bird has lost
all power of directing its actions so as to gratify the desire. But
these effects are only observed when the whole of both hemispheres have
been removed. If a small portion remain the bird retains most of its
faculties, though with less energy. In frogs and fishes there is little
discernible effect observed when a large portion of the cerebrum is
removed.
31. Now take away from this mutilated bird its cerebellum: all the
functions continue as before except that _some_ combined movements can
no longer be effected; flight is impossible; walking is a mere stagger.
Remove only the lateral lobes, and though flight is still possible
great _incoherence_ of the wings is observed, whereas walking is not
much affected. If only the cerebellum be removed, the cerebrum being
intact, the phenomena are very different. All the perceptions and
almost all the emotions, all the spontaneity and vivacity are retained;
but the sexual instinct, which was manifested when the cerebrum was
removed, is now quite gone. What we call Intelligence seems unaffected.
The bird hears, and understands the meaning of the sounds, sees and
perceives, sees and fears, sees and adjusts its movements with a mental
vision of unseen consequences.[92]
32. Are we from these facts to conclude that the cerebrum is the “organ
of the mind”; that it is “the seat” of sensation, thought, emotion,
volition; and that the cerebellum is the “seat” of the sexual instinct,
and muscular co-ordination? Such conclusions have found acceptance,
even from physiologists who would have been startled had any one
ventured to affirm that the medulla oblongata was the “organ” of
Respiration, because Respiration ceases when this centre is destroyed.
I shall have to combat this notion at various stages of my exposition.
Here let me simply say that it is irreconcilable with any clear
conception of organ and function; and is plainly irreconcilable with
any survey of psychical phenomena in animals in whom the cerebrum does
not exist, and in animals from whom it has been removed.
What the facts indisputably prove is that the cerebrum has an important
part in the mechanism by which the most complex psychical combinations
are effected, and that the cerebellum has an important part in the
mechanism by which the most complex muscular combinations are
effected. The supreme importance of the cerebrum may be inferred from
its dominating all the other centres, and from its preponderance in
size. In man it stands to all the other cranial centres together in
the relation of 11 to 3. It is about five times as heavy as the spinal
cord--that is to say from 1,100 to 1,400 grammes, compared with 27 to
30 grammes. The quantity of blood circulating through it is immense.
Haller estimated the cranial circulation as one fifth of the whole
circulation. If, therefore, the Nervous Centres are agents in the
production of Sensation and Intelligence, by far the largest share must
be allotted to the cranial centres, and of these the largest to the
Cerebrum.
33. It is, however, one thing to recognize the Cerebrum as having
an important part in the production of psychical phenomena, another
thing to localize all the phenomena in it as their organ and seat--a
localization which soon becomes even more absurd, when of all the
cerebral structure the multipolar cells alone are admitted as the
active agents!
As was said just now, we recognize in the Medulla Oblongata the nervous
centre of Respiration, but we do not suppose that Respiration has its
_seat_ there, nor that this centre is absolutely indispensable for
the essential part of the process. We respire by our skin, as well as
by our lungs; many animals respire who have nothing like a medulla
oblongata; as many animals feel, and manifest will, who have nothing
like a cerebrum. The destruction of centres is of course a disturbance
of the mechanisms which they regulate. But even the observed results
of a destruction require very close examination, and are liable to
erroneous interpretations. The disappearance of a function following
the destruction, or disease of a particular part, is not to be accepted
as a proof that this part is the organ of the lost function; because
precisely the same phenomena may often be observed following the
destruction of a totally different part.[93] But one result may always
be relied on, and that is the _persistence_ of a function after removal
of a particular part. Thus there is a certain spot of the cerebral
convolutions from which movements of the limbs are excited when the
electrodes are applied to it; removal of the substance is immediately
followed by paralysis of the limbs. Are we to conclude that this spot
is the organ of the function? It is true that the function is called
into action by a stimulus applied to this spot: true that the function
suddenly vanishes when the substance of this spot is destroyed.
Nevertheless, what seems a loss of function is only a disturbance. In
two or three days the paralysis begins to disappear, and at the end
of a week the limbs are moved nearly in the normal manner. And the
same is true when the spot in question is destroyed on both sides. The
recovery of the function shows that the absent part was not its organ.
There is a paradoxical experiment recorded by M. Paul Bert which may be
cited here. He removed the right cerebral hemisphere from a chameleon,
and found that the limbs on the left side were paralyzed; but on his
then removing the left cerebral hemisphere the limbs of the left side
recovered their activity. A similar result was obtained by Lussana and
Lemoigne by extirpation of the thalami. When we find combined movements
persisting after the cerebellum has been destroyed, we may be sure that
the cerebellum is not the organ by which such combinations take place;
and when we find sensation and volition manifested after the cerebrum
has been removed, we may be sure that the cerebrum is not the organ for
these sensations and volitions.
34. And this we do find. Physiologists, indeed, for the most part,
deny it; or rather, while they admit the observed facts, they refuse
to admit the only consistent interpretation, biassed as they are by
the traditional conception of the brain. After having for many years
persistently denied Sensibility to any centre except the cerebrum, they
are now generally agreed in including the medulla oblongata within the
privileged region; but they still exclude the medulla spinalis.
35. If all the cranial centres as far as the medulla oblongata are
removed from young rabbits, dogs, or cats, there are unmistakable
evidences of Sensibility in their _cries_ when their tails are pinched,
their _moving jaws_ (as in mastication) when bitters are placed in
their mouths, and their _raised paws rubbing their noses_, when
irritating vapors are applied. It is said indeed that the cries are no
signs of _pain_; and this is probable; but they are assuredly signs of
Sensibility.
35. The frog thus mutilated has lost indeed all its special senses,
except Touch, but it still breathes, struggles when grasped, thrusts
aside the pincers which irritate it, or wipes away acid dropped on its
skin. If the eye be lightly touched, the eyelid closes; if the touch
be repeated three or four times, the foreleg is raised to push the
irritant away; if still repeated, the head is turned aside; but however
prolonged the irritation, the frog neither hops, nor crawls away, as he
does when the cerebellum remains. Place the brainless frog on his back,
and if the medulla oblongata remains he will at once regain the normal
position; but if that part is absent he will lie helpless on his back.
The power of preserving equilibrium in difficult positions--which
of course implies a nice co-ordination of muscles--resides in the
so-called _optic lobes_ of the frog (what in mammals are called the
_corpora quadrigemina_).
37. With the destruction of each part of the central mass there will
necessarily be some disturbance of the mechanism; but difficult as
may be the task of detecting by experiment what is the normal action
of any one part, there ought to be no hesitation in recognizing the
persistence of functions after certain parts are destroyed. The
spinal cord is anatomically known to be the centre from which the
limbs, trunk, and genito-urinary organs are innervated. So long as
the mechanism of the actions involving such organs is intact, no
removal of other parts will prevent this mechanism from exhibiting its
normal action. There may indeed arise, and there has arisen, the doubt
whether Sensibility is involved in the action of any nerve centre below
the medulla oblongata. But this doubt is founded on the traditional
hypothesis respecting the seat of Sensation, and is flagrantly at
variance with the logical conclusions of Anatomy and Experiment.
38. Anatomy shows that the structure of the spinal cord is in all
essential characters the same as that of the medulla oblongata; and
indeed that the whole central axis has one continuous tissue, somewhat
variously arranged, and in relation with various organs.
Abundant Experiment has shown that the spinal cord, apart from the
encephalon, is capable of acting as a sensorial and volitional centre.
The striking facts advanced by Pflüger, Auerbach, and myself, have
not been impugned;[94] but their interpretation has been generally
rejected. We showed that a brainless frog responded to stimulation in
actions which bore so close a resemblance to actions admitted to be
sensorial and volitional--showed the frog _adapting_ itself to new
conditions, and _acquiring_ dexterity in executing actions which at
first were impossible or difficult, _devising_ combinations to effect
a purpose which never by any possibility could have formed part of its
habits--manifesting, in a word, such signs of Sensibility, that no one
witnessing the experiments could hesitate as to the interpretation, had
he not been biassed by the traditions of the schools.
39. Our opponents argued that in spite of all appearances there
were profound differences between the actions of the normal and the
brainless animal, and that the latter were due simply to Reflex Action.
I also insist on profound differences; but underlying these there
are fundamental identities. As to the Reflex Action, two points will
hereafter be brought forward: 1°, that _all_ central action is reflex,
the cerebral no less than the spinal; 2°, that the hypothesis of Reflex
Action being purely _mechanical_, and distinguished from Voluntary
Action in not involving Sensibility, is an hypothesis which must be
relinquished.
40. Postponing, however, all discussion of these points, let me here
say that the doctrine maintained in these pages is that the whole
cerebro-spinal axis is a centre of Reflexion, its various segments
taking part in the performance of different kinds of combined action.
It has one common property, Sensibility; and different parts of it
minister to different functions--the optic centre being different from
the auditory, the cerebral from the spinal; and so on. To make this
intelligible, however, we must first learn what is known respecting the
properties of nerve-tissue.
CHAPTER III.
NEURILITY.
41. Observation having found that the activity of a nerve was always
followed by a sensation when the nerve ended in a centre, and by a
movement when the nerve ended in a muscle, Theory was called upon
to disclose the nature of this peculiar property of nerves. That a
peculiar and mysterious power did act in the nerves no one doubted;
the only doubt was as to its nature. The ancient hypothesis of Animal
Spirits seemed all that was needed. The spirits coursed along the
nerves, and obeyed the mandates of the Soul. When this hypothesis fell
into discredit, its place was successively taken by the hypotheses of
Nervous Fluid, Electricity, and Nerve Force. The Fluid, though never
manifested to Sense, was firmly believed in, even so late as the days
of Cuvier;[95] but when the so-called electrical currents were detected
in nerves, and the nervous phenomena were shown to resemble electrical
phenomena, there was a general agreement in adopting the electrical
hypothesis. The brain then took the place of a galvanic battery; the
nerves were its electrodes.
42. Closer comparison of the phenomena detected various irreconcilable
differences, which, if they proved nothing else, proved that
nerve-action took place under conditions so special as to demand a
special designation. Electricity itself is so little understood, that
until its nature is more precisely known, we cannot confidently say
more than that nerve-action resembles electrical-action; meanwhile the
speciality of neural conditions renders all deduction illusory which
is based on electrical-action as observed under _other_ conditions.
In presence of these difficulties, cautious physiologists content
themselves with assigning the observed phenomena to the observed
and inferred conditions, condensing these in the convenient symbol
“nerve-force,” without pretending to any specification of the nature
of that force. It may be a wave of molecular movement dependent on
isometric change or on metamorphic change. It may be the liberation of
molecular tension resembling electricity; it may be electricity itself.
But whatever the nature of the change, it is an activity of the tissue,
and as such comes under the general dynamic conception of Force or
Energy.
43. In this sense the term has nothing equivocal or obscure.
It is a shorthand expression symbolizing certain well-defined
observations. Nevertheless, it is a term which we shall do well to
avoid when possible, and to replace by another having less danger of
misinterpretation; the reason being that Force has become a sort of
shibboleth, and a will-o’-wisp to speculative minds. All that we _know_
of Force is Motion. But this is too meagre for metempirical thinkers,
who disdain the familiar experiences expressed in the term Motion,
and demand a transcendent cause “to account” for what is observed.
They seek an entity to account for the fact. Motion is a very definite
conception, expressing precise experiences; we know what it means, and
know that the laws of moving bodies admit of the nicest calculation.
A similar precision belongs to Force when understood as “mass
acceleration,” or M V². But this does not content those metaphysicians
who understand by Force “the unknown reality behind the phenomena”--the
_cause_ of Motion. This cause they refuse to recognize in some
antecedent motion (what I have termed a “differential pressure”), but
demand for it a physical or metaphysical _agent_: the physical agent
being a subtle fluid of the nature of Ether, or a nerve atmosphere
surrounding the molecules; the metaphysical agent being a Spirit or
aggregate of Soul-atoms. The second alternative we may decline here
to discuss. The first alternative is not only a pure fiction, but one
which is inconsistent with the demonstrable velocity of the neural
process, which is not greater than the pace of a greyhound, whereas
the velocities of light and electricity are enormously beyond this. It
is inconsistent also with the observation that a much feebler current
of electricity is requisite for the stimulation of a muscle through
its nerve than when directly applied to the muscle: a proof that the
nerve does not act solely by transmission of electricity--unless we
gratuitously assume that the nerve is a multiplicator.
When it is said that the living nerve is incessantly liberating Force
which can be communicated to other tissues, the statement is acceptable
only if we reject the metaphysical conceptions it will too generally
suggest--the conceptions of Force as an entity, and of its being
passed from one object to another like an arrow shot from a bow. The
physical interpretation simply says that the molecules of the nerve are
incessantly vibrating, and with varying sweep; these vibrations, when
of a certain energy, will set going vibrations in another substance by
disturbing the tension of its molecules, as the vibrations of heat will
disturb the tension of the gunpowder molecules, and set them sweeping
with greater energy: this is the _communication_ of the force. Just as
we say that a magnet communicates magnetic force to a bit of iron,
though all we mean is that the magnet has so altered the molecular
condition of the iron as to have given it the movements called
magnetism--in short, has excited in the iron the dormant property of
becoming magnetic--so we say the nerve communicates its force to the
muscle, exciting in the muscle its dormant property of contraction.
But in truth nothing has passed from magnet to iron, or from nerve to
muscle.
44. Do what we will, however, there is always, in the present condition
of philosophical chaos, the danger of being misunderstood when we
employ the term Nerve-force; and I have proposed the term Neurility as
an escape from the misleading suggestions. It is a symbol expressing
the general property of nerve-tissue. For reasons presently to be
stated, I restrict Neurility to the peripheral system, employing
Sensibility for the central system. The excited muscle manifests its
special property of Contractility; the excited nerve manifests its
special property of Neurility; the excited centre manifests its special
property of Sensibility.[96] The terms are simply descriptive, and
carry with them no hypothesis as to _what_ Neurility is in its hidden
process, nor _how_ Sensibility arises in a nerve-centre, and not
elsewhere. We know that a stimulated muscle contracts, and we express
the fact by assigning to muscular tissue the property of Contractility.
We know that a stimulated nerve translates an impulse from one point to
another, and excites the muscle to contract; and we express the fact
by assigning to nerve-tissue the property of transmitting stimulation,
which is further specified, as unlike other transmissions, by the term
Neurility.
45. What is the meaning attached to the term Property, and how it is
distinguished from Function, has been already expounded in Problem
1, §§ 81–6. There also was laid down the principle of _identity of
structure implying identity of property_. Inasmuch as observation
reveals a fundamental similarity in the structure of the nervous tissue
throughout the animal kingdom, we must conclude the existence of a
fundamental similarity in the property of that tissue: a conclusion
confirmed by observation. There is a corresponding agreement in the
organs and functions; so that, within certain limits, the experiments
performed on an insect may be verified on a mammal. Everywhere
nerve-tissue has certain characters in common, accompanied by
variations in the degree and mode of manifestation corresponding with
variations in structure and connection. Obvious as the fact is, we
must emphasize the great variety which accompanies the underlying
uniformity, for this is recognizable both in the individual organism
and in the animal kingdom at large. Even such seemingly individual
terms as nerve-cell and nerve-fibre are in truth generic; and the
description which accurately represents one cell or fibre needs
modifying for others.
Properties are generalized expressions; they result from the
_composition_, the _structure_, and the _texture_ of a substance. Thus
one bar of iron may differ from another of equal bulk in being more or
less crystalline in structure, though having the same composition and
the same texture. This difference will modify the mode of manifestation
of the iron-properties. Cast-iron pillars, for example, will support,
as a roof, a weight which would break them if suspended; wrought-iron
pillars of similar bulk will bear a weight suspended which would crush
them as a roof. Yet both cast and wrought iron pillars have the same
properties, because they have the _same_ composition and _similar_
structure; the variation of structure only producing a difference in
the modes. Texture may also vary. The bar of iron may be beaten into
a plate, rolled into a cylinder, or split into wire-work, without any
change in its properties, but with marked differences in its modes of
manifestation, and in the _uses_ to which it may be applied. These uses
are of course dependent on the connections established between the iron
and other things. In Physiology, _uses_ are called _functions_.
46. Nerve-tissue must be understood as having everywhere the same
general Property. In one animal and in another, in one part and in
another, Neurility is the same in kind, but not everywhere manifesting
the same degree, nor applied to the same Function. The _composition_
of nerve-tissue varies, but not more than the composition of all other
organized substances; the _structure_ is variable, but only within
a small range; the _texture_ also; while the _connections_ are very
various. Hence, whatever the variations in composition or structure,
the nerve-fibre has everywhere one fundamental property, which in
connection with a muscle has the functional activity of exciting
contraction; in connection with a gland of exciting secretion; and in
connection with a centre of exciting reflexion.[97]
47. Had a clear idea of Function as dependent on connexion been present
to their minds certain physiologists would hardly have raised the
mirage of “Nerve-force,” a mysterious entity endowed with “specific
energies,” and capable of producing vital and psychical phenomena by
an occult process; nor would others have been led to the monstrous
hypothesis of particular nerve-cells being endowed with thought,
instinct, and volition. They would have sought an explanation of
functions in the combined properties of the co-operant organs and
tissues. They would not have endowed one nerve with Sensibility, and
another nerve of identical structure with Motility;[98] one nerve with
a motor property, and another with the opposite property of inhibition.
They would have seen that all nerves have the same _property_, but
different _uses_ when in different connexions.
48. Throughout the animal kingdom we see movement following on
stimulation. Stimulation may be defined the change of molecular
equilibrium. The stimulation of a muscle is produced indirectly through
a change in the nerve, or directly through a change in the muscle
itself. In the simplest organisms there is no trace of nerve-tissue;
but their substance manifests Irritability (or as it is often called
Sensibility); and a stimulus to one part is propagated throughout--the
whole body moves when touched. Even in Polypes, where there is the
beginning of a differentiation, the motion is slowly propagated from
one part to the rest. A single tentacle retracts when touched; but the
movement rarely ends there; it is slowly communicated from one tentacle
to the other, and from them to the whole mass. Touching the body,
however, will not, if the touch be slight, cause the tentacles to move;
so that we see here a beginning of that principle of specialization
which is so manifest in the higher organisms: the tentacles have
become the specially sensitive parts. Ascending higher in the scale of
organisms we find those which habitually move particular parts without
at the same time necessarily moving the rest; and this independence
of parts, accompanying a more perfect consensus, we find to be
developed _pari passu_ with a nervous system. An immense variety of
part-movements, with varying combinations of such movements, is the
physiological expression of the more complex nervous system.
48 _a_. Deferring what has to be said of Sensibility till the next
chapter, we may here touch on its relation to Irritability, which is
often used as its synonym. _Objectively_ it cannot be distinguished
from Irritability, nor indeed from the most general phenomenon of
reaction under stimulation; in this it is an universal property. But
_subjectively_ it is distinguishable as a peculiar mode of reaction,
only known in nerve-tissues. While all tissues are irritable, and react
on being stimulated, each tissue has its special mode of reaction. The
secreting-cell reacts differently from the muscle-cell. The reaction
of the nerve is the innervation of a centre or a muscle; the reaction
of an innervated centre is sensation; of a muscle, contraction. There
are three aspects of neural reaction: excitation, propagation of the
disturbance, and innervation. The first is expressed by irritability,
the second by conductibility, the third by sensibility; but these are
only artificial distinctions in the general phenomenon of transmitted
excitation. The nerve substance is specially distinguished by its
instability of molecular equilibrium; it undergoes chemical change
with a readiness comparable to that of explosive substances. Hence
its facility of propagation of disturbance. There is irritability and
propagation of disturbance in muscular tissue, notably evident in
the continuous tissue of the heart, intestines, and ureter; but the
propagation is slow and diffusive; whereas in the nerve it is rapid,
and restricted along a definite path. By this rapidity and restriction
the force of the impact is increased; and thus a slight stimulus
applied to the nerve is capable of disturbing the state of the muscle.
49. Thus while molecular movement is a fundamental condition of
Vitality, and is incessant throughout organized substance, the massive
movements of the organism, and the movements of particular parts, are
the _directed quantities_ of this molecular agitation. They are due
to stimulation. We distinguish this from mechanical impulsion. It
is a vital process involving molecular change; it is not simply the
_communication_ of motion from without, but the _excitation_ of motion
within. It is not like the blow which merely displaces an object, but
like the blow which disturbs its molecular equilibrium. The effect,
therefore, depends on this molecular condition: the blow which scatters
a heap of gunpowder will explode a fulminating salt, and this, in
exploding, will excite the gunpowder to explode. The stimulus which
is too feeble to excite contraction in a muscle will be powerful
enough to excite the neurility of a nerve, and _that_ will excite the
contractility of the muscle. The nerve-force is simply neural stimulus.
It acts upon the other tissues as the nitrogenous salt upon the
gunpowder.
Although it is now common to speak of nerves as transmitting waves of
molecular motion, and to regard nerves as the passive medium for the
“transference of force,” whereby the force is thus made an abstract
entity, we must always remember that such phrases are metaphors, and
that the truer expression will be not “transference of force,” but the
“propagation of excitation.” I mean that it is not the _force_ of the
impact nor its _energy_ which a nerve transmits, it is the vibratory
change produced in the nerve by the impact, which excites another
change in the organ to which the nerve goes. We know by accurate
measurements that the excitation of a nerve lasts much longer than the
_stimulus_, a momentary impact producing an enduring agitation. We know
also that the excitation of a centre lasts longer than the muscular
contraction it has initiated. We know, moreover, that a nerve may be
totally incapable of conducting an external stimulus, yet quite capable
of conducting a central stimulus; were it a passive conductor like a
wire this would not be so.[99]
50. The nerve is essentially an exciter of change, and thereby a
regulator. A muscle in action does not appreciably determine action
in any other (except in the comparatively rare cases of anastomosing
muscles); a secreting cell does not propagate its excitation to others.
The nerve, on the contrary, not only propagates its excitation, and
awakens the activity of the muscle or gland with which it is connected,
but through the centre affects the whole organism--
“Ein Schlag tausend Verbindungen schlägt.”
Thus it is that stimulation which in the simpler organisms was diffused
throughout the protoplasm, has in the complex organisms become the
specialized property of a particular tissue.
51. Two general facts of supreme importance must now be stated: One is
the law of stimulation--_every excitation pursues the path of least
resistance_. The second is the condition of stimulation--_unlike
mechanical impulsion, it acts only at insensible distances_.
52. This means that although a nerve may be excited by any stimulus
external to it which changes its molecular condition, no propagation of
that change (i. e. no stimulation through the nerve) is possible except
through continuity of substance. Mere physical contact suffices to
excite the nerve; but if there be an interruption of continuity in the
nerve itself, no stimulus-wave passes across that line. Cut a nerve,
and bring the divided surfaces once more into close contact, there will
still be such a solution of continuity as to arrest the stimulus-wave,
mere physical contact not sufficing for the propagation. Whereas across
the cut ends of a divided nerve, even visibly separated, the electric
current easily passes. This necessity for the vital continuity of
tissue in the propagation of stimulation must always be borne in mind.
The presence of a membrane, however delicate, or of any tissue having
a different molecular constitution, suffices to arrest or divert the
wave. I conceive, therefore, that it is absolutely indispensable that
a nerve should terminate in and _blend_ with a muscle or a centre,
otherwise no stimulation of muscle or centre will take place through
the nerve.
[Illustration: Fig. 13.]
53. The difference between excitation from contact and stimulation
from continuity may be thus illustrated. In Fig. 13 we see the legs
of a frog attached to the spine by the lumbar nerves (_l_), and lying
on the muscles (_m_) of one leg is the nerve (_c_) of another frog’s
leg. Applying the electrodes to (_l_), the muscles (_m_) are violently
contracted; not only so, but their contraction excites the other nerve
(_c_), and the leg attached to this nerve is thereby thrown into
contraction. This “secondary contraction,” as Dubois Reymond calls it,
might be supposed to be due to a diffusion of the electrical current;
but that it is due to a change in the muscles (_m_) is proved by
delicate experiments showing that the movements in the detached leg are
of precisely the same kind as those in the legs directly stimulated.
If there is only a muscular shock in the one case, there is only a
muscular shock in the other; if there is tetanus in the one, there is
tetanus in the other; if the muscles of the first leg are fatigued
and respond slowly and feebly, the response of the second is slow and
feeble. Moreover, the secondary contraction may be produced by chemical
or mechanical stimulus, as well as by the electrical.
54. Although the contraction of a muscle is thus seen to be capable
of exciting a nerve in contact with it, the reverse is not true: we
can produce no contraction in a muscle by exciting a nerve simply in
contact with the muscle, and not penetrating its tissue and terminating
there. Accordingly we always find a nerve when about to enter a muscle
or a centre losing its _protecting_ envelopes; it gradually becomes
identified as a protoplasmic thread with the protoplasm of the muscle
or the centre.
55. Neurility, then, is the propagation of molecular change. Two
offices are subserved by the nervous system, which may respectively be
called Excitation--the disturbance of molecular _tension_ in tissues,
and consequent liberation of their energies; and Co-ordination--the
direction of these several energies into combined actions. Thus, when
the muscle is in a given state of molecular tension, the stimulation of
its nerve will change that state, causing it to contract if it be in
repose. But this stimulation, which will thus cause a contraction, will
be arrested, if at the same time a more powerful stimulation reaches
the antagonist muscle, or some distant centre: then the muscle only
_tends_ to contract.
ORIGIN OF NERVE-FORCE.
56. After this brief account of Neurility we may pass to the
consideration of its origin. Are we to understand that this property
belongs to the nerves themselves in the sense in which Contractility
belongs to the muscles? or are we to accept the teaching which assigns
the origin of “nerve-force” to the ganglia, and regards the nerves
simply as passive conductors of a force developed in the cells?
57. It is now many years since I ventured to criticise the reigning
doctrine, and to urge the necessity Of consistently carrying out the
distinction between Property and Function. I called attention to the
positive evidence which contradicted the idea of passive conduction;
and pointed out the illusory nature of the favorite analogy, in which
ganglia were likened to batteries, and nerves to the conducting wires.
But the old image still exerts its empire; and writers are still
found speaking of the brain as a telegraphic bureau, the ganglia as
stations, and the nerves as wires. In the cells of the gray substance
they place a constantly renewing reservoir of nerve-force. There the
force is elaborated, stored up, and from thence directed along the
nerves. The sensory nerve “transmits an impression to the brain”--as
the wire transmits a message to the bureau. The motor nerve, in turn,
“transmits the mandates of the will”--and all is clear! Clear, until
we come to translate metaphors into visible facts, or try to conjure
up some mental image of the process. For myself, I can only conceive
nerve-force as the activity of the nerve, and not of something
_else_. This becomes still more evident when I find that the activity
is equally manifest after its imaginary source has been removed.
Transmitting impressions, or messages, implies as a preliminary that
there should be an impressible agent, or a _message-sender_, at the
periphery. No one supposes that simply touching one end of a wire
would send an “impression” or a “message” to the battery; or that
without the battery this touch would evolve a current. The battery is
indispensable; in _it_ is evolved the current which the wire transmits.
Not so the ganglion, or brain. Remove the wire from its connection with
the battery, and it is a bit of wire, nothing more. But remove a nerve
from its connection with a ganglion, and it is still active as nerve,
still displays its Neurility when excited, still moves the muscle as
before. The amputated limb will move when its nerves are stimulated,
just as when a reflex from its centre moved it. Every one knew the
fact; it was staring them in the face, yet they disregarded it. Even
the old anatomist, Willis, had recorded experiments which ought to have
opened their eyes. He tied the phrenic nerve, and found that, when
he irritated it below the ligature, the diaphragm moved; but when he
irritated it above the ligature, no movement followed. Since his days,
thousands of experiments have shown that the presence of a ganglion is
not necessary to the action of a nerve.[100]
58. Of course an explanation was ready. The nerve was said to have been
“endowed with force” from its ganglion during their vital connection;
and this force, stored up in the nerve, was disposable for some time
after separation from the ganglion. We need not pause to criticise this
misty conception of one part “endowing” another with force; the plain
facts afford the best answer. There seemed, indeed, a confirmation
of the hypothesis in the fact that although the nerve separated from
its ganglion was capable of excitation, yet after a few excitations
it was exhausted, and ceased to stimulate the muscle. It seemed like
the piece of magnetized iron which would act as a temporary magnet,
though quickly losing this borrowed power. But the whole fabric
fell--or ought to have fallen--when extended observation discovered
that this exhausted nerve would, if left in repose, _recover_ its
lost power. A nerve preserves its excitability as long as it preserves
its structural integrity, and recovers its power in recovering that
integrity. The length of time varies.[101] Gratiolet found the muscles
in the leg of a tortoise, which had been amputated a week before,
contract when the nerves were irritated; and Schiff found the divided
nerve of a winter frog excitable at the end of three weeks. Even
after all excitability has disappeared, it will reappear if arterial
blood be injected; just as muscles which have already begun to assume
cadaveric rigidity recover their contractility after transfusion. Nor
is this all. The separated nerve finally degenerates, and loses all its
structural characters and physiological properties; yet under favorable
conditions it will regenerate--recover its structures and properties;
and this even apart from a centre, as Vulpian showed. Very noticeable
is the fact that the force said to be produced in the centre, and only
“conveyed” by the nerve, vanishes gradually from the centre to the
periphery, and recovers from the periphery to the centre--the part of
the nerve which is farthest from the centre being excitable when the
part nearest the centre is still inexcitable. Again, when a nerve is
pinched, contraction in the muscle follows; but the pinch has for a
time so disturbed the structural integrity of the nerve (at that spot)
that no irritant applied to the spot, or _between_ it and the centre,
will be followed by contraction, whereas _below_ the spot an irritation
takes effect. This is another form of the experiment of Willis. Even in
its normal state, the nerve has different degrees of excitability in
different parts of its course,--a fact discovered by Pflüger which is
quite irreconcilable with the hypothesis of passive conduction. Doubts
have been thrown on Pflüger’s interpretation,[102] namely, that there
is an avalanche-like accumulation of energy proportionate to the length
of the stimulated portion; but the fact remains, that one and the
same irritant applied successively to two different points of a nerve
does not irritate the muscle in the same degree. Munk also finds the
velocity of transmission in a motor nerve increases as it approaches
its termination in the muscle.[103]
59. Nothing can be more unlike the conduction of an electric current
than this excitation of Neurility; nothing more accordant with the
idea of it as a vital property of the tissue. The notion of its being
derived from a centre is on a par with the notion first successfully
combated by Haller,[104] that the muscle derived its Contractility
from the nerves; or the analogous notion that the electric organ
in fishes derived its property from the brain. Indeed, it was in
support of the hypothesis that the brain was a battery, and nerves
the conductors, that the phenomena observed in electrical fishes were
frequently cited. The electric organ was seen to be connected with
the brain; its discharges were under the control of the animal, and
were destroyed on one side when the brain on the corresponding side
was destroyed. But Charles Robin long ago suggested, what indeed ought
never to have been doubted, that the brain was not the source of the
electricity; but that the tissue of the electric organ itself had this
special property, which the nerve merely called into activity. The
suggestion has been experimentally verified by M. Moreau, who divided
all the nerves supplying the electric organ on one side, and, having
thus cut off all communication with the brain, produced electrical
discharges by irritating the nerves; precisely as the muscles are made
to contract when the divided nerves are irritated. Had the experiment
ceased here, it might have been interpreted on the old hypothesis: the
electric organ might be supposed to have a certain amount of electric
force condensed in it, stored up there, as it is said to be in the
nerves, and discharged when the organ is irritated. But experiment has
decided this point also. Electric fishes notoriously exhaust their
power by a few discharges, and recover it after repose. When M. Moreau
had exhausted his mutilated fishes, he replaced them in the water,
and allowed them repose. On again irritating the divided nerves, the
discharges were again produced.[105]
60. On all sides the idea of nerves deriving their power from another
source than their own substance is seen to be untenable. _A priori_
this might have been concluded. Neurility is the vital property of
nerve-tissue. “Nerve-force” is nerve-action--molecular changes in the
nerve itself, not in some remote substance. That nerve and centre are
vitally connected is true; and what their physiological relations are
will hereafter be examined; but we must dismiss the idea of nerves
having the relation to centres that electrodes have to batteries.
61. In proposing the term Neurility, I not only wished to get rid of
the ambiguities which hovered round “nerve-force” and “nerve-current,”
but to recall the physiological principle that properties are
dependent on structures; and therefore that the special property of
nerve-tissue is conditioned by its structure. Neurility is, of course,
an abstraction; but so is _the_ nerve an abstraction. The concrete
manifestations are the several nerve-actions. These we classify and
specify. One class we call sensory, another class motor; not because
the nerve-action itself is different, but because it is in each class
in a different functional relation to other parts. In classing men
as governors and governed, employers and employed, we do not suppose
anthropological distinctions, but only differences in their social
functions.
62. This is the modification of the Law of Bell to which reference was
made in § 26. It replaces the idea of two different kinds of nerve,
sensory and motor, by that of two different anatomical connections. I
need not reproduce here the argument with which I formerly criticised
the supposed distinction between sensory and motor nerves; because
the old idea is rapidly falling into discredit, and physiologists so
eminent as Vulpian and Wundt have explicitly announced their adhesion
to the principle of identity,--a principle which, as Vulpian truly
remarks, dominates the whole physiology of the nervous system.[106]
THE HYPOTHESIS OF SPECIFIC ENERGIES.
63. One development of the theory of Bell, respecting the different
kinds of nerve, has been the still accredited hypothesis that each
nerve has a “specific energy,” or quality, in virtue of which it
acts and reacts only in one way. The optic nerve, no matter how
stimulated, only responds by a sensation of color, the auditory nerve
only by a sensation of sound; and so on. This hypothesis, which (as
I learn from a correspondent)[107] was originally propounded by Bell
himself, was developed and made an European doctrine by Johannes
Müller, first in his remarkable treatise, _Über die phantastischen
Gesichtserscheinungen_ (1826), and afterwards in his _Physiology_.
Like all good hypotheses, it has been fruitful; and Helmholtz
still holds it to be of extraordinary importance for the theory of
perception. Although combated by a few physiologists, it has kept its
place firm in the general acceptance; no doubt because it forms a ready
explanation of the facts. But, as I often have to remark, _explanation_
is not _demonstration_.[108]
64. The first criticism to be made on the hypothesis is that it
commits the error of confounding function with property, assigning as
a specific quality of the nerve the reaction of the organ innervated.
Thus Müller speaks of the specific energy as “the essential condition
of the nerves in virtue of which they see light and hear sound.”
But the optic nerve no more _sees_, than the liver-nerve _secretes_
bile. That the optic nerve is one element in the mechanism on which
vision depends, is all that we can say, Müller declares that it is
not sufficient to assume each nerve to be so constituted that it
has a susceptibility to certain stimuli rather than to others; but
that “with Aristotle we must ascribe to each a peculiar energy as
its vital quality. Sensation,” he adds, “consists in the sensorium
receiving through the medium of the nerves a _knowledge of certain
qualities_,--a condition, not of the external bodies, but of the
nerves themselves,”--and these qualities are different in different
nerves. In other words, he assumes a special substance for each special
energy. The sensation of color depends on the special Visual substance
(_Sehsinnsubstanz_); the sensation of sound on the Auditory substance
(_Hörsinnsubstanz_); and so on.
65. We have here an hypothesis analogous to that of Innate Ideas, or
_a priori_ Forms of Thought. It is, in fact, only a reproduction of
that conception carried into the sphere of Sense. No one thinks of
assigning specific energies to the several muscles, yet a movement of
prehension is as different from a movement of extension, a peristaltic
movement is as different from a movement of occlusion, as a sensation
of sound is from a sensation of color. If movement is common to both
of the one class, feeling is common to both of the other: the forms
and mechanism are different and specific. Muscles have the common
property of contracting under stimulation; whatever be the nature of
the stimulus, each muscle has its own particular response, or mode of
reaction: the flexor always bending, never extending the limb; the
sphincter always closing, never opening the orifice. The movements
of the heart are not the same as those of the eye; both are unlike
the movements of the intestine. There are muscles which respond to
some stimuli, and not to others. Those of the eye, or of the vocal
chords, respond to impulses which would leave the masseter or biceps
unstirred. According to Marey, the hyoglossus of a frog will become
tetanic under a stimulus of only ten pulses in a second; whereas the
gastrocnemius of that same frog resists a stimulus of less than twenty
in a second. We find the retina responding to ethereal pulses which
leave the auditorius unaffected; we find the muscles of a gnat’s wing
so exquisitely susceptible that the wing beats eight thousand times in
a second,--a delicacy in comparison with which even our muscles of the
eye are coarse.
66. The facts which the hypothesis of specific energies is called
on to explain are more consistently interpreted on the admission of
a common property in nerve-tissue, manifesting different degrees of
excitability, and entering into different mechanisms, so that the
functional results differ. A nerve which may be stimulated from the
skin will not respond at all, or not in the same way, if the stimulus
be applied under the skin. Are we to suppose that the specific energy
resides in one part of the nerve, and not in another?[109] That the
optic nerve responds to stimuli which will not sensibly excite a
motor nerve, depends on the terminal structures through which the
stimulation is excited; for the optic nerve itself, apart from the
retinal expansion, is as insensible to light as the motor nerve is. And
the specific sensation, or movement, which _results_ from stimulation
of a nerve depends not on the nerve, but on the mechanism of which the
nerve is one element. Sensations of touch, temperature, and pain are
assuredly specific; they are as unlike each other as a sensation of
taste is unlike a sensation of smell. Yet the same nerves, variously
stimulated, produce all three sensations.
67. We conclude, therefore, that the phrase “specific energy” is an
elliptical expression for the particular office of a nerve. In this
meaning there is no obscurity. The optic nerve is not a vasomotor
nerve, the skin nerve is not a muscle nerve; the auditory nerve is a
nerve of special sensation, the vagus is a nerve of systemic sensation;
and so on. Neither movement nor sensation belongs to the nerves
themselves.
CHAPTER IV.
SENSIBILITY.
68. The principles laid down in the preceding chapter are equally
applicable to the central system. But here greater difficulties await
us. We cannot expect traditional views to be easily displaced, when
they have taken such hold on the mind, as is the case with regard to
Sensibility. To admit that all nerves have a common property, and that
their functional relations depend on the organs which they innervate,
demands small relinquishment of cherished opinions. But to admit that
all nerve-centres have a common property, and that their functional
relations depend on their anatomical connections, is to sweep away at
once a mass of theoretic interpretations which from long familiarity
have acquired an almost axiomatic force. That the brain, and the brain
only, is the source and seat of Sensibility is the postulate of modern
Physiology.
69. The question is one of extreme complexity, but may be greatly
simplified, if we can manage to reduce it to purely physiological
terms, and consider the phenomena in their objective aspect. In dealing
with nerves and their actions this was comparatively easy; we had for
the most part only physiological processes to unravel. It is otherwise
in dealing with nerve-centres--the subjective or psychological aspect
of the phenomena inevitably thrusts itself on our attention; and all
the mysteries of Feeling and Thought cloud our vision of the neural
process. Do what we will, we cannot altogether divest Sensibility of
its psychological connotations, cannot help interpreting it in terms
of Consciousness; so that even when treating of sensitive phenomena
observed in molluscs and insects, we always imagine these more or less
suffused with Feeling, as this is known in our own conscious states.
70. Feeling is recognized as in some way or other bound up with
neural processes; but Physiology proper has only to concern itself
with the processes; and the question whether these can, and do, go on
unaccompanied by Feeling, is, strictly speaking, one which belongs
to Psychology. It demands as a preliminary that the term Feeling be
defined; and the answer will depend upon that definition, namely,
whether Feeling be interpreted as synonymous with Consciousness in the
restricted sense, or synonymous with the more general term Sentience.
If the former, then since there are unquestionably neural processes of
which we are not conscious, we must specify the particular groups which
subserve Feeling; as we specify the particular groups which subserve
the sensations of Sight, Hearing, Taste, etc.; and localize the
separate functions in separate organs. If the latter, then, since all
neural processes have a common character, we have only to localize the
particular variations of its manifestation, and distinguish sensitive
phenomena as we distinguish motor phenomena.
71. It is absolutely certain that the Feeling we attribute to a
mollusc is different from that which we attribute to a man; if only
because the organisms of the two are so widely different, and have
been under such different conditions of excitation. If every feeling
is the functional result of special organic activities, varying with
the co-operant elements, we can have no more warrant for assuming the
existence of the same _particular_ forms of Feeling in organisms
that are unlike, than for assuming the 47th proposition of Euclid to
be presented by any three straight lines. The lines are the necessary
basis for the construction, but they are not the triangle, except when
in a special configuration. This is not denying that animals _feel_
(in the general sense of that term), it is only asserting that their
feelings must be very _unlike_ our own. Even in our own race we see
marked differences--some modes of feeling being absolutely denied to
individuals only slightly differing from their fellows. If, however,
we admit that different animals must have different modes of Feeling,
we must also admit that the neuro-muscular activities are generically
alike in all, because of the fundamental similarity in the structures.
Whether we shall assign Feeling to the mollusc or not will depend on
the meaning of the term; but, at all events, we require some term
general enough to include the phenomena manifested by the mollusc,
and those manifested by all other animals. Sensibility is the least
objectionable term. Unless we adopt some such general designation,
physiological and psychological interpretations become contradictory
and obscure. The current doctrine which assigns Sensibility to the
brain, denying it to all other centres, is seriously defective,
inasmuch as it implies that tissues similar in kind have utterly
diverse properties; in other words, that the same nerve-tissue which
manifests Sensibility in the brain has no such property in the spinal
cord.
72. How is this tenable? No one acquainted at first hand with the facts
denies that the objective phenomena exhibited by the brainless animal
have the same general character as those of the animal possessing a
brain: the actions of the two are identical in all cases which admit
of comparison. That is to say, the objective appearances are the
same; differing only in so far as the mechanisms are made different
by the presence or absence of certain parts. The brain not being a
necessary part of the mechanical adjustments in swimming, or pushing
aside an irritating object, the brainless frog swims and defends itself
in the same way as the normal frog. But no sooner do we pass from
the objective interpretation, and introduce the subjective element
of Feeling among the series of factors necessary to the product--no
sooner do we ask whether the brainless frog _feels_ the irritation
against which it struggles, or _wills_ the movements by which it
swims--than the question has shifted its ground, and has passed from
Physiology to Psychology. The appeal is no longer made to Observation,
but to Interpretation. Observation tells us here nothing directly
of Feeling. What it does tell us, however, is the identity of the
objective phenomena; and Physiology demands that a common term be
employed to designate the character common to the varied phenomena.
Sensibility is such a term. But most modern physiologists, under the
bias of tradition, refuse to extend Sensibility to the spinal cord,
in spite of the evidences of the spinal cord possessing that property
in common with the brain. They prefer to invoke a new property; they
assign spinal action to a Reflex Mechanism which has nothing of the
character of Sensibility, because they have identified Sensibility with
Consciousness, and have restricted Consciousness to a special group of
sensitive phenomena.
73. Nor is it to be denied that on this ground they have a firm basis.
Every one could testify to the fact that many processes normally
go on without being accompanied by consciousness, in the special
meaning of the term. Reflex actions,--such as winking, breathing,
swallowing,--notoriously produced by stimulation of sensitive surfaces,
take place without our “feeling” them, or being “conscious” of them.
Hence it is concluded that the Reflex mechanism suffices without the
intervention of Sensibility. I altogether dispute the conclusion; and
in a future Problem will endeavor to show that Sensibility is necessary
to Reflex Action. But without awaiting that exposition we may at once
confront the evidence, by adducing the familiar fact that “unconscious”
processes go on in the brain as well as in the spinal cord; and this
not simply in the sphere of Volition, but also in the sphere of
Thought.[110] We act and think “automatically” at times, and are quite
“unconscious” of what we are doing, or of the data we are logically
grouping. We often think as unconsciously as we breathe; although from
time to time we become conscious of both processes. Yet who will assert
that these unconscious processes were independent of Sensibility?
Who will maintain that because cerebral processes are sometimes
unaccompanied by that peculiar state named Consciousness, therefore all
its processes are unaccompanied by Feeling? And if here we admit that
the Reflex mechanism in the brain is a _sensitive_ mechanism, surely we
must equally admit that the similar Reflex mechanism in the spinal cord
is sensitive?
74. Let it be understood that Sensibility is the common property of
nerve-centres, and physiological interpretations will become clear
and consistent. Consciousness, as understood by psychologists, is not
a property of tissue, it is a function of the organism, dependent
indeed on Sensibility, but not convertible with it. There is a greater
distinction between the two than between Sensation, the reaction of
a sensory organ, and Perception, the combined result of sensory and
cerebral reactions; or than that between Contractility, the property of
the muscles, and Flying, the function of a particular group of muscles.
It is not possible to have Consciousness without Sensibility; but
perfectly possible to have Sensations without Consciousness. This will
perhaps seem as inconceivable to the reader as it seemed to Schröder
van der Kolk.[111]
75. Let us illustrate it by the analogy of Pain. There is a vast amount
of sensation normally excited which is totally unaccompanied by the
feelings classed as painful. The action of the special senses may be
exaggerated to an intolerable degree, but the exaggeration never passes
into pain: the retina may be blinded with excess of light, and the ear
stunned with sound--the optic nerve may be pricked or cut--but no pain
results. The systemic sensations also are habitually painless, though
they pass into pain in abnormal states. Clearly, then, Pain is not the
necessary consequence of Sensibility; and this is true not only of
certain sensitive parts, but of all; as is proved in the well-known
facts of Analgesia, in which complete insensibility of the skin as
regards Pain co-exists with vivid sensibility as regards Touch and
Temperature. Hence the majority of physiologists refuse to acknowledge
that the struggles and cries of an animal, after removal of the brain,
are evidences of pain; maintaining that they are “simply reflex
actions.” This is probable; the more so as we know the struggles and
cries which tickling will produce, yet no pain accompanies tickling.
But if the struggles and cries are not evidence of pain, they are
surely evidence of Sensibility.
76. Now for the term Pain in the foregoing paragraph substitute the
term Consciousness, and you will perhaps allow that while it may be
justifiable to interpret the actions of a brainless animal as due to a
mechanism which is unaccompanied by the _specially conditioned forms_
of Sensibility classed under Consciousness--just as it is unaccompanied
by the specially conditioned forms of Perception and Emotion--there
is no justification for assuming the mechanism not to have been a
_sensitive_ mechanism. The wingless bird cannot manifest any Of the
phenomena of flight; but we do not therefore deny that its _other_
movements depend on Contractility.
77. Difficult as it must be to keep the physiological question apart
from the psychological when treating of Sensibility, we shall never
succeed in our analysis unless the two questions are separately
treated. The physiologist considers organisms and their actions
from their objective side, and tries to detect the mechanism of the
observed phenomena. These he has to interpret in terms of Matter and
Motion. The psychologist interprets them in terms of Feeling. The
actions which we _see_ in others we cannot _feel_, except as visual
sensations; the changes which we feel in ourselves we cannot see in
others, except as bodily movements. The reaction of a sensory organ is
by the physiologist called a sensation,--borrowing the term from the
psychologist; he explains it as due to the stimulus which changes the
molecular condition of the organ; and this changed condition, besides
being seen to be followed by a muscular movement, is _inferred_ to
be accompanied by a change of Feeling. The psychologist has direct
knowledge only of the change of Feeling which follows on some other
change; he infers that it is originated by the action of some external
cause, and infers that a neural process precedes, or accompanies, the
feeling. Obviously there are two distinct questions here, involving
distinct methods. The physiologist is compelled to complete his
objective observations by subjective suggestions; compelled to add
Feeling to the terms of Matter and Motion, in spite of the radical
diversity of their aspects. The psychologist also is compelled to
complete his subjective observations by objective interpretations,
linking the internal changes to the external changes. A complete theory
must harmonize the two procedures.
78. In a subsequent Problem we shall have to examine the nature of
Sensation in its psychological aspect; here we have first to describe
its physiological aspect. To the psychologist, a sensation is simply a
fact of Consciousness; he has nothing whatever to do with the neural
process, which the physiologist considers to be the physical basis
of this fact; and he therefore regards the physiologists as talking
nonsense when they talk of “unconscious sensations,” the phrase being
to him equivalent to “unfelt feelings,” or “invisible light.” It is
quite otherwise with the physiologist, who viewing a sensation solely
as a neural process, the reaction of a sensory organ, can lawfully
speak of unconscious sensations, as the physicist can speak of
invisible rays of light,--meaning those rays which are of a different
order of undulation from the visible rays, and which may become visible
when the susceptibility of the retina is exalted. He knows that there
are different modes, and different complexities of neural process; to
one class he assigns consciousness, to the other unconsciousness. If he
would be severely precise, he would never speak of sensation at all,
but only of sensory reaction. But such precision would be pedantic and
idle. He wants the connotations of the term sensation, and therefore
uses it.
79. The functional activity of a gland is stimulated by a neural
process reflected from a centre; by a similar process a muscle is
called into action. No one supposes that the neural process is, in
the one case secretory, in the other motory: in both it is the same
process in the nerve; and our investigation of it would be greatly
hampered if we did not disengage it from all the suggestions hovering
around the ideas of secretion and muscular action. In like manner
we must disengage the neural process of a sensory reaction from all
the suggestions hovering around the idea of Consciousness, when that
term designates a complex of many reactions. In Problem III. we shall
enter more particularly into the distinction between Sensibility and
Consciousness; for the present it must suffice to say that great
ambiguity exists in the current usage of these terms. Sometimes
Consciousness stands as the equivalent of Sensibility; sometimes as a
particular _mode_ of Sensibility known as Reflection, Attention, and
Thought. The former meaning is an extension of the term similar to
that given to the word Rose, which originally meaning Red came to be
restricted to a particular red flower; and after other flowers of the
same kind were discovered which had yellow and white petals, instead
of red, the term rose still adhered even to these. “Yellow Rose” is
therefore as great a verbal solecism as unconscious sensation. We have
separated the redness from the rose, and can then say that the color
is one thing, the flower another. By a similar process of abstraction
we separate Consciousness from Sensation, and we can then say that
there are sensations without consciousness. In consequence of this,
psychologists often maintain that to have a sensation and be conscious
of it are two different states. We are said to hear a sound, and yet
not to be conscious of hearing it. The sound excites a movement, but
it does not excite our consciousness. Now although it is true that
there are roses which are not red, it is not true that there are
roses which have no color at all. Although it is true that there are
sensations which are not of the particular mode of Sensibility which
psychologists specially designate as Consciousness, it is not true
that there are sensations which are not modes of Sensibility.
80. And what is Sensibility which, on its subjective side, is
Sentience? In one sense it may be answered that we do not know. In
another sense it is that which we know most clearly and positively:
Sentience forms the substance of all knowledge. Being the ultimate of
knowledge, every effort must be vain which attempts to explain it by
reduction to simpler elements. The human mind, impatient of ultimates,
is always striving to pierce beyond the fundamental mysteries; and this
impatience leads to the attempts so often made to explain Sensibility
by reducing it to terms of Matter and Motion. But inasmuch as a clear
analysis of Matter and Motion displays that our knowledge of these is
simply a knowledge of modes of Feeling, the reduction of Sentience or
Sensibility to Matter and Motion is simply the reduction of Sensibility
to some of its modes. This point gained, a clear conception of the
advantages of introducing the ideas of Matter and Motion will result.
It will then be the familiar and indispensable method of explaining
the little known by the better known. The objective aspect of things
is commonly represented in the visible and palpable; because what we
can see we can also generally touch, and what we can touch we can
taste and smell; but we cannot touch an odor nor a sound; we cannot
see them; we can only connect the odorous and sonorous objects with
visible or palpable conditions. Everywhere we find sensations referred
to visible or palpable causes; and hence the desire to find this
objective basis for every change in Sensibility. The sensation, or
state of consciousness, is the ultimate fact; we can only _explain_ it
by describing its objective conditions.
81. Thus much on the philosophical side. Returning to our physiological
point, we must say that a sensation is, objectively, the reaction
of a sensory organ, or organism; subjectively, a change of feeling.
Objectively it is a phenomenon of movement, but distinguishable
from other phenomena by the speciality of its conditions. It is a
vital phenomenon, not a purely mechanical phenomenon. Although the
molecular movement conforms, of course, to mechanical principles, and
may be viewed abstractly as a purely mechanical result, yet, because
it takes place under conditions never found in machines, it has
characters which markedly separate it from the movements of machines.
Among these differential characters may be cited that of _selective
adaptation_,[112] which is most conspicuous in volition.
82. In the early stages of animal evolution there is no differentiation
into muscle and nerve. The whole organism is equally sensitive (or
irritable) in every part. Muscles appear, and then they are the most
sensitive parts. Nerves appear, and the seat of Sensibility has
been transferred to them; not that the muscles have lost theirs, but
their irritability is now represented by their dominant character of
Contractility, and the nerves have taken on the special office of
Sensibility. That is to say, while both muscle and nerve form integral
elements of the sensitive reaction, the process itself is analytically
conceived as a combination of two distinct properties, resident in two
distinct tissues.
83. Carrying further this analytical artifice, I propose to distinguish
the central organs as the seat of Sensibility, confining Neurility to
the peripheral nerves. In physiological reality both systems, central
and peripheral, are one; the separation is artificial. Strictly
speaking, therefore, Neurility--or nerve-action--is the general
property of nerve-tissue, central and peripheral. But since Neurility
may be manifested by nerves apart from centres, whereas Sensibility
demands the co-operation of both, and since we have often to consider
the central process in itself, without attending to the process in the
nerves, it is well to have two characteristic terms. I shall therefore
always use the term Sensibility for the reactions of the nervous
centres,--Sentience being its psychological equivalent; although the
reader will understand that in point of fact there is no break, nor
transformation, as the wave of change passes from sensory nerve to
centre, and from centre to motor nerve: there is one continuous process
of change. But just as we analytically distinguish the sensory from
the motor element of this indissoluble process, so we may distinguish
the ingoing and outgoing stages from the combining stage. Sensibility,
then, represents the property of _combining_ and grouping stimulations.
84. Fully aware of the misleading connotations of the term, and of the
difficulty which will be felt in disengaging it from these, especially
in reference to Consciousness, I have long hesitated before adopting
it. But the advantages greatly outweigh the disadvantages. Sensibility
has long been admitted to express the peculiar modes of reaction in
plants and animals low down in the scale. No one hesitates to speak of
a sensitive plant, or a sensitive surface. The tentacles of a polype
are said to be sensitive; though probably no one thereby means that
the polype has what psychologists mean by Consciousness. By employing
the general term Sensibility to designate the whole range of reactions
peculiar to the nerve-centres, when these special organs exist, it
will be possible to interpret all the physiological and psychological
phenomena observed in animals and men on one uniform method. The
observed variations will then be referable to varieties in organisms.
85. Suppose, for illustration, an organism like the human except
that it is wholly deficient in Sight, Hearing, Taste, and Smell. It
has no sense but Touch--or the general reaction under contact with
external objects. It will move on being stimulated, and will combine
its movements differently under different stimulations. It will feel,
and logically combine its feelings. But its mass of feeling will be
made of far simpler elements than ours; its combinations fewer; and
the contents of its Consciousness so very different from ours that
we are unable to conceive what it will be like; we can only be sure
that it will _not_ be very like our own. This truncated Organism will
have its Sensibility; and we must assign this property to its central
nerve-tissue, as we assign our own. If now we descend lower, and
suppose an organism with no centres whatever, but which nevertheless
displays evidence of Sensibility--feelings and combinations of
movements--we must then conclude that the property specialized in
a particular tissue of the highly differentiated organism is here
diffused throughout.
It is obvious that the sensations or feelings of these supposed
organisms will have a common character with the feelings of more highly
differentiated organisms, although the modes of manifestation are so
various. If we recognize a common character in muscular movements so
various as the rhythmic pulsation of the heart, the larger rhythm of
inspiration and expiration, the restless movements of the eye and
tongue, the complexities of manipulation, the consensus of movements in
flying, swimming, walking, speaking, singing, etc., so may we recognize
a common character in all the varieties of sensation. The special
character of a movement depends on the moving organ. The special
character of a sensation depends on the sensory organ. Contractility
is the abstract term which expresses all possible varieties of
contraction. Sensibility--or Sentience--is the abstract term which
expresses all possible varieties of sensation.
86. The view here propounded may find a more ready acceptance when its
application to all physiological questions has been tested, and it is
seen to give coherence to many scattered and hitherto irreconcilable
facts. Meanwhile let a glance be taken at the inconsistencies of the
current doctrine. That doctrine declares one half of the gray substance
of the spinal cord to be capable only of _receiving_ a sensitive
stimulation, the other half capable only of _originating_ a motor
stimulation. We might with equal propriety declare that one half of a
muscle is capable only of receiving a contractile stimulation, and the
other half of contracting. The ingoing nerve, passing from the surface
to the posterior part of the spinal cord, excites the activity of the
gray substance into which it penetrates; with the anterior part of
this gray substance an outgoing nerve is connected, and through it
the excitation is propagated to a muscle: contraction results. Such
are the facts. In our analysis we separate the sensory from the motor
aspect, and we then imagine that this ideal distinction represents a
real separation. We suppose a phenomenon of Sensibility independent of
a phenomenon of Contractility--suppose the one to be “transformed” into
the other--and we then marvel “how during this passage the excitation
changes its nature.”[113]
87. Before exerting ingenuity in explaining a fact, it is always well
to make sure that the fact itself is correctly stated. _Does_ the
neural excitation change its nature in passing from the posterior to
the anterior gray substance? I can see no evidence of it. Indeed the
statement seems to confound a neural process with a muscular process.
The neural process is one continuous excitation along the whole line
of ingoing nerve, centre, and outgoing nerve, which nowhere ceases
or changes into another process, until the excitation of the muscle
introduces a new factor. So long as the excitation keeps within the
nerve-tissue, it is one and the same process of change; its issue
in a contraction, a secretion, or a change in the conditions of
consciousness, depends on the organs it stimulates.
88. I have already called attention to the artificial nature of all our
distinctions, and the necessity of such artifices. They are products of
that
“Secondary power
By which we multiply distinctions, then
Deem that our puny boundaries are things
That we perceive, and not that we have made.”[114]
The distinction of Central and Peripheral systems is not simply
anatomical, it has a physiological justification in this, that the
Central System is the organ of connection. Any one part of it directly
excited by an ingoing nerve propagates that excitation throughout
the whole central mass, and thus affects every part of the organism.
Therefore we place Sensibility in it.
But this general Property subserves various Functions, according as the
Central System is variously related to different organs. This fact has
given rise to the idea that different portions of the cerebro-spinal
axis have different properties--which is a serious error. What is
certain is that the Cerebrum must have a different function from that
of the Thalami, and the Cerebellum one different from the Medulla
Oblongata; while that of the Medulla Spinalis is different from all.
Precisely on the same grounds that a muscle-nerve has a different
office from a skin-nerve, or the pneumogastric from the acoustic.
But all nerves have one Neurility in common; all centres have one
Sensibility in common.
CHAPTER V.
ACTION WITHOUT NERVE-CENTRES.
89. It has long been one of the unquestioned postulates of Physiology
that no nerve-action can take place without the intervention of a
centre; and as a corollary, that all movement has its impulse--reflex
or volitional--from a centre.[115] The postulate rests on the
assumption that nerves derive their “force” from their centre. This
assumption we have seen to be erroneous. Yet, in consequence of its
acceptance, experimenters have failed to notice the many examples of
nerve-action independent of centres. Indeed, except Schiff, Goltz, and
Engelmann, I can name no one who has ventured to suggest that movements
may be excited through nerves without the co-operation of centres;[116]
nor have even they explicitly formulated the conclusion to which their
observations point.
It is true that the majority of muscular movements are determined by a
reflex from centres; and that any break in the triple process of the
ingoing nerve, centre, and outgoing nerve, prevents such movements.
It is true that the more conspicuous and harmoniously co-ordinated
phenomena belong to this class. But it is also demonstrable that many
nerve-actions _may_, and some _do_, take place by direct stimulation
of the nerve, or direct stimulation of the muscle, without the
intervention of a centre, without even the intervention of a ganglion.
This must obviously be the case in animals which have no centres; and
even in some which have well-developed nervous centres, there is every
reason to believe that these centres often act rather in the way of
co-ordinating than of directly stimulating actions.
90. I was first led to doubt the reigning doctrine by a surprising
observation (frequently repeated) after I had removed the whole nervous
centres from a garden snail (_Helix pomatia_). The muscular mass called
“the foot” was thrown into slow but energetic contraction whenever the
skin was pricked with the point of a scalpel, or touched with acid;
nay, even when a glass rod dipped in the acid was brought close to,
without absolutely touching, the skin, the foot curled up, and then
slowly relaxed. The same effect was produced on the “mantle”--where
there was of course no centre. But direct irritation of the muscles
under the skin produced no such contraction; only through the skin
could the stimulation take effect. In one case I observed this strange
phenomenon five hours after removal of the centres. It was a great
puzzle. At first I concluded that there must be minute ganglia in
the skin, serving as reflex-centres. I searched for them in vain;
and although a longer search on better methods might _possibly_ have
detected ganglionic cells, I soon relinquished the search, because I
had other grounds for believing that even the presence of abundant
ganglia would not suffice, until some better proof were afforded that
such ganglia were reflex-centres.
91. That direct stimulation of the nerve suffices to move the muscles,
is familiar to all experimenters. There is no centre, or ganglion,
in the amputated leg of the frog, which nevertheless contracts
whenever the sciatic nerve is stimulated. And after the nerve has been
exhausted, and refuses to respond to any stimulus, the muscle itself
may be directly stimulated. Inasmuch as the movement depends on the
contractility of the muscles, a stimulation through centre, through
motor-nerve, or through muscle, will be followed by contraction. Let
us take a clear case of reflex action. The pupil of the eye contracts
when a beam of light falls on it, and dilates when the beam is shut
off. The path of the neural process is normally this: the light
stimulates the optic nerve, which in turn stimulates the corpora
quadrigemina; (here the nerves which move the eye are experimentally
proved to be stimulated;) and it is through these that the pupil is
caused to contract. If the optic nerve be divided, no such reflex takes
place--proving that the contraction does not, at least normally, come
from the ciliary ganglion.
But now it is matter of observation that the pupil will contract and
dilate under the stimuli of light and darkness, when there is no such
reflex pathway open. Removal of the eye from the body obliterates
this path, cuts the eye off from all connection with the centre.
Brown Séquard removed both eyes from a frog, placed one in a dark
box, and left the other exposed to the light: the pupil of the former
was found dilated, that of the latter contracted. On reversing the
experiment, and placing the eye with contracted pupil in the dark
box, he found it there dilate, while the dilated pupil exposed to
the light contracted.[117] In frogs with very irritable tissues, I
have found not only the pupil contracting, after the whole cranial
cavity has been emptied, but even the eyelid close, on irritating
the conjunctiva[118]--yet this is one of the typical reflex actions!
I am disposed to think that even the action of swallowing may be
faintly excited by stimulation of the pharynx of a brainless frog; but
I have not observations sufficiently precise to enable me to speak
confidently. Goltz has, however, shown that after removal of brain
and spinal cord and heart, there is spontaneous and active movement
in œsophagus and stomach.[119] This will no doubt be referred to the
agency of the ganglionic plexus; but similar movements have been
observed by Engelmann in the ureter, and in isolated fragments of the
ureter in which not a ganglionic cell was present.[120]
92. That nerves are stimulated by internal changes has long been
recognized with reference to “subjective sensations.” The divided
nerve, in that portion which remains connected with the centre, will
at times cause great pain. Obscure organic conditions, changes of
temperature, states of the blood, excite the nerves, and the patient
feels as if the surface of the amputated limb were irritated. It is
all very well to call these “subjective sensations”; that does not
alter the fact of the nerve being called into activity by other than
the normal stimuli from the surface; in like manner muscular movements
(which are not to be explained as “subjective movements”) will be
excited by organic stimuli when motor-nerves are separated from their
centres. In each case it has sufficed that the nerve should be excited;
and when excited, no matter by what means, the effect is always similar.
93. Here are a few facts. Stimulation of the nerves which send
filaments to the chromatophores of the skin in reptiles causes the skin
to become paler, and even colorless: the color-specks disappear under
this contractile stimulus. This being known, Goltz deprived a frog of
brain, spinal cord, and heart, thus eliminating all possible influence
from them, slit up the skin of the back, and displayed the nerves which
pass from each side of the spine to the skin; these nerves he then
divided on the right side, and observed the skin on this side slowly
become paler and paler, till finally it was as yellow as wax; the left
side, having its nerves intact, retained its color. Two conclusions
seemed to him warranted by this experiment: First, that even in the
dead frog the nerves separated from their centre were still active;
secondly, that the irritation of the nerves resulting from their
section was the cause of the color-specks disappearing. This second
conclusion was strengthened when he found that the irritation was
increased when he cut the nerves bit by bit.
It is not at present, I believe, clearly made out that the color-specks
of the Cephalopoda are in direct connection with nerves; but it is
tolerably certain that they are in some way under the influence of
nervous stimulation, directly or indirectly. D’Orbigny, indeed, goes
so far as to say they are dependent on the will of the animal.[121]
This seems very lax language; but restricting ourselves to the fact
of nervous influence, the experiments of Goltz receive further
illustration in an observation I have elsewhere recorded.[122] I found
that a strip of skin taken from the dead body of a calamary (_Loligo_)
showed the color-specks expanding and contracting with vigor.
94. The heart is well known to beat after death, if death be not the
result of a gradual decay. Sometimes, indeed, its muscular irritability
is so active that the heart will beat for hours. E. Rousseau
observed it beating in a woman twenty-seven hours after she had been
guillotined.[123] Not only will it beat after death, but in many
animals even after removal from the body: the heart of a young puppy,
or kitten, will beat for three or four hours after its removal; that
of a full-grown dog, or cat, not one hour; whereas the beating of that
of a tortoise, or a frog, will, under proper precautions, be preserved
for days--and even after it has stopped, it may be stimulated to fresh
pulsations.
Physiologists explain this spontaneous movement of the heart as due to
the ganglia in its substance. This explanation, which is founded on
what I cannot but regard as a purely imaginary view of the functions
of ganglionic cells, must stand or fall with that hypothesis. A long
and arduous investigation has led me to doubt whether in _any_ case
the heart’s movements are primarily due to its ganglia; at all events,
the same spontaneous movements are observed in the hearts of molluscs
and crustaceans, which are without even a trace of ganglia; and in the
hearts of mammalian embryos long before ganglia or nerve-fibres make
their appearance. Not less certain is it that movements of contraction
and dilatation are produced in the blood-vessels independently of all
central influence. This has been decisively proved by the Italian
physiologist, Mosso, when experimenting on an organ isolated from the
organism; and although the vessels have their nerve cells and fibres,
he justly doubts whether it is to these that the stimulation is due,
because the phenomena are observed after the nervous vitality has
disappeared. Goltz severed all the tissues in the leg of a rabbit,
so that the only connection of the leg with the rest of the body was
through the crural vein and artery, which kept up the circulation; yet
although the nerves of the skin were thus separated from their centre,
so that no sensation could be produced by stimulating the skin of the
leg, consequently no reflex from the centre on the vessels, Goltz found
that a marked reddening of the skin from congestion of the capillaries
followed the application of mustard to the skin. Physiologists who
believe that the constriction and dilatation of blood-vessels are due
to the action of the ganglionic cells distributed over the walls of the
vessels will explain Goltz’s observation as a case of reflex action;
but those who agree with me that such an hypothesis respecting the part
played by the cells is untenable, will class the observation among
other cases of direct stimulation.
95. But passing from these perhaps questionable cases, let us glance
at other cases. The mobile iris of the bird displays movements after
the nerves have been divided. Even the voluntary striped muscles are
not altogether motionless. Schiff divided the hypoglossus on one side,
and found, of course, the tongue paralyzed on that side; but he also
found that on the third day after the operation some of the muscles of
that side were quivering: the agitation spread to others, till by the
end of the fourth day all the fibres were _rhythmically_ contracting.
From this time onwards, the contractions were incessant; though they
were never able to move the tongue, because the fibres did not contract
simultaneously.
Schiff also observed that the hairs over the eyes and the “whiskers” of
cats, rabbits, and guinea pigs were for months after section of their
nerves in incessant rhythmical vibration. This was observed when the
animals were asleep as when awake. Valentin records the spontaneous
movements in the diaphragm of animals just killed; and this even after
section of the phrenic nerve. The same movements may be seen in the
operculum of fishes. Henle observed the spontaneous contractions of the
intercostal muscles; which Schiff confirms, adding that the movements
observed by him in cats and birds were not simply contractions of some
fibres, but of all the muscles, so that three or four excised ribs
rhythmically contracted and expanded.
I have performed a great many experiments with a view of determining
this question, but the phenomena were so variable that I refrain
from adducing any,[124] and merely state the general result as one
in harmony with the foregoing examples. The great variability of the
phenomena depends upon the variable conditions of muscular irritability
and anatomical relations. When the heart of one woman is found beating
twenty-seven hours after death, while in most men and women it ceases
after a few minutes, we must be prepared to find different, and even
contradictory phenomena under varying unknown conditions. There
is, however, a general agreement among experimenters that muscular
irritability increases after separation from nerve-centres, and then
quickly decreases again.
96. Although the stimulation of muscles usually comes _through_ a
nerve-centre, yet since the muscles do not derive their Contractility
from nerve-centres any stimulation will suffice. Now since we have
abundant proof that sensory nerves are stimulated by certain organic
changes, by poisons in the blood, excess of carbonic acid, etc., we
are justified in concluding that motor nerves will be stimulated in
like manner, and thus muscular movement be produced occasionally
without the intervention of a centre. Pressure on a motor nerve, or the
irritation which results from inflammation, will determine contraction,
or secretion directly. Recently, Erb and Westphal have disclosed
the fact that the leg will be suddenly jerked out if the patella be
gently tapped; and they prove this not to be a reflex action, because
it follows with the same certainty after the skin has been made
insensible.[125]
There are doubtless many other phenomena which, though commonly
assigned to reflex stimulation, are really due to direct stimulation.
Research might profitably be turned towards the elucidation of this
point. Since there is demonstrable evidence that a nerve when no
longer in connection with its centre, or with ganglionic cells, may
be excited by electricity, pressure, thermal and chemical stimuli, we
must conclude that even when it is in connection with its centre, any
local irritation from pressure, changes in the circulation, etc., will
also excite it. But as such local excitations will have only local and
isolated effects, they will rarely be conspicuous.
CHAPTER VI.
WHAT IS TAUGHT BY EMBRYOLOGY?
97. Subject to the qualification expressed in the last chapter,
stimulation of muscles and glands involves a neural process in ingoing
nerve, centre, and outgoing nerve. These are the triple elements of the
“nervous arc.” If muscles were directly exposed to external influences,
they would be stimulated without the intervention of a centre; but as a
matter of fact they never are thus exposed, being always protected by
the skin. Did the skin-nerves pass directly to the muscles underneath,
they would move those muscles, without the intervention of a centre;
but as a matter of fact the skin-nerves pass directly to a centre, so
that it is only _through_ a centre that they can act upon the muscles.
Were muscles and glands directly connected with sensitive surfaces,
their activity would indeed be awakened by direct stimulation; but
unless the muscles were so connected the one with the other, by
anastomosis of fibres or continuity of tissue, that the movement of
one was the movement of all, there would need to be some other channel
by which their separate energies should be combined and co-ordinated.
In the higher organisms anastomosis of muscles is rare, and the
combination is effected by means of the nerves.
98. Although analysis distinguishes the two elements of the
neuro-muscular system, assigning separate properties to the separate
tissues, an interpretation of the phenomena demands a synthesis, so
that a movement is to be conceived as always involving Sensibility,
and a sensation as always involving Motility.[126] In like manner,
although analysis distinguishes the various organs of the body,
assigning separate functions to each, our interpretation demands their
synthesis into an organism; and we have thus to explain how the _whole_
has different _parts_, and how these different parts are brought into
unity. Embryology helps us to complete the fragmentary indications of
Anatomy and Physiology.
99. Take a newly laid egg, weigh it carefully, then hatch it, and when
the chick emerges, weigh both chick and shell: you will find that
there has been no increase of weight. The semifluid contents have
become transformed into bones, muscles, nerves, tendons, feathers,
beak, and claws, all without increase of substance. There has been
_differentiation_ of structure, nothing else. Oxygen has passed into
it from without; carbonic acid has passed out of it. The molecular
agitation of heat has been required for the rearrangements of the
substance. Without oxygen there would have been no development. Without
heat there would have been none. Had the shell been varnished, so as to
prevent the due exchange of oxygen and carbonic acid, no chick would
have been evolved. Had only one part of the shell been varnished, the
embryo would have been deformed.
99_a_. The patient labors of many observers (how patient only those
can conceive who have made such observations!) have detected something
of this wondrous history, and enabled the mind to picture some of the
incessant separations and reunions, chemical and morphological. Each
stage of evolution presents itself as the consequence of a preceding
stage, at once an emergence and a continuance; so that no transposition
of stages is possible; each has its appointed place in the series
(PROBLEM I. § 107). For in truth each stage is a _process_--the sum of
a variety of co-operant conditions. We, looking forward, can foresee in
each what it will become, as we foresee the man in the lineaments of
the infant; but in this prevision we always presuppose that the regular
course of development will proceed unchecked through the regular
succession of special conditions: the infant becomes a man only when
this succession is uninterrupted. Obvious as this seems, it is often
disregarded; and the old metaphysical conception of _potential_ powers
obscures the real significance of Epigenesis. The potentiality of the
cells of the germinal membrane is simply their capability of reaching
successive stages of development under a definite series of co-operant
conditions. We foresee the result, and personify our prevision. But
that result will not take place unless all the precise changes that
are needful serially precede it. A slight pressure in one direction,
insufficient to alter the chemical composition of the tissue, may so
alter its structure as to disturb the regular succession of forms
necessary to the perfect evolution.
100. The egg is at first a microscopic cell, the nucleus of which
divides and subdivides as it grows. The egg becomes a hollow sphere,
the boundary wall of which is a single layer of cells, all so
similar that to any means of appreciation we now possess they are
indistinguishable. They are all the progeny of the original nucleus
and yolk, or cell contents. Very soon, however, they begin to show
distinguishable differences, not perhaps in _kind_, but in _degree_.
The wall of this hollow sphere is rapidly converted into the _germinal
membrane_, out of which the embryo is formed. Kowalewsky (confirmed by
Balfour) has pointed out how in the Amphioxus the hollow sphere first
assumes an oval shape, and then, by an indentation of the under side,
with corresponding curvature of the upper side, presents somewhat
the shape of a bowl. The curvature increases, and the curved ends
approaching each other, the original cavity is reduced to a thin line
separating the upper from the under surface. The cavity of the body is
formed by the curving downwards of this double layer of the germinal
membrane.
101. This is not precisely the course observable in other vertebrates;
but in all, the germinal membrane, which lies like a watch-glass on the
surface of the yolk, is recognizable as two distinct layers of very
similar cells. What do these represent? They are the starting-points
of the two great systems: Instrumental and Alimental. The one yields
the dermal surface; the other the mucous membrane. Each follows an
independent though analogous career. The yolk furnishes nutrient
material to the germinal membrane, and so passes more or less directly
into the tissues; but unlike the germinal membrane, it is not itself
to any great extent the seat of generation by segmentation. There are
two yolks: the yellow and the white (which must not be confounded
with what is called the _white of egg_); and their disposition may be
seen in the diagram (Fig. 14) copied from Foster and Balfour’s work.
The importance of the white yolk is that it passes insensibly into
a distinct layer of the germinal membrane, between the two primary
layers.[127] Each of the three layers of the germinal membrane has its
specific character assigned to it by embryologists, who, however, are
not all in agreement. Some authorities regard the topmost layer as
the origin of the nervous system, the epidermis, with hair, feathers,
nails, horns, the cornea and lens of the eye, etc. To the middle layer
are assigned the muscular and osseous systems, the sexual organs, etc.
To the innermost layer, the alimentary canal, with liver, pancreas,
gastric and enteric glands. Other authorities are in favor of two
primary layers: one for the nervous, muscular, osseous, and dermal
systems; the other for the viscera and unstriped muscles. Between these
two layers, a third gradually forms, which is specially characterized
as the vascular.
[Illustration:
Fig. 14.--_Diagrammatic section of an unincubated hen’s egg._ _bl_,
blastoderm; _w y_, white yolk; _y y_, yellow yolk; _v t_, vitelline
membrane; _x_ and _w_, layers of albumen; _ch l_, chalaza; _a ch_,
air-chamber; _i s m_, internal layer of shell membrane; _s m_,
external layer; _s_, shell.
]
102. Messrs. Foster and Balfour, avoiding the controverted designations
of serous, vascular, and mucous layers, or of sensorial, motor
germinative, and glandular layers, employ designations which are
independent of theoretic interpretation, and simply describe the
position of the layers, namely, _epiblast_ for the upper, _mesoblast_
for the middle, and _hypoblast_ for the under layer. From the epiblast
they derive the epidermis and central nervous system (or would even
limit the latter to the central gray matter), together with some
parts of the sense-organs. From the mesoblast, the muscles, nerves
(and probably white matter of the centres), bones, connective tissue,
and blood-vessels. From the hypoblast, the epithelial lining of the
alimentary canal, trachea, bronchial tubes, as well as the liver,
pancreas, etc.[128] Kölliker’s suggestion is much to the same effect,
namely, that the three layers may be viewed as two epithelial layers,
between which subsequently arises a third, the origin of nerves,
muscles, bones, connective tissue, and vessels.[129]
103. The way in which the history may be epitomized is briefly this:
There are two germinal membranes, respectively representing the
Instrumental and Alimental Systems. Each membrane differentiates, by
different appropriations of the yolk substance, into three primary
layers, _epithelial_, _neural_, and _muscular_. In the epiblast, or
upper membrane, these layers represent: 1°, the future epidermis
with its derivatives--hair, feathers, nails, skin glands, and
chromatophores; 2°, the future nervous tissue; 3°, the future muscular
tissue.[130] (Bone, dermis, connective tissue, and blood-corpuscles are
subsequent formations.)
The hypoblast, or under membrane, in an inverted order presents a
similar arrangement: 1°, the unstriped muscular tissue of viscera and
vessels; 2°, the nervous tissue of the sympathetic system; 3°, the
epithelial lining of the alimentary canal with its glands.
Fundamentally alike as these two membranes are, they have specific
differences; but in both we may represent to ourselves the
_embryological unit_ constituted by an epithelial cell, a nerve-cell,
and a muscle-cell. All the other cells and tissues are adjuncts,
necessary, indeed, to the working of the vital mechanism, but
subordinated to the higher organites.
104. This conception may be compared with that of His in the
division of Archiblast and Parablast assigned by him to the germ
and accessory germ.[131] We can imagine, he says, the whole of the
connective substances removed from the organism, and thus leave behind
a scaffolding in which brain and spinal cord would be the axis,
surrounded by muscles, glands, and epithelium, and nerves as connecting
threads. All these parts stand in more or less direct relation to the
nervous system. All are continuous. By a similar abstraction we can
imagine this organic system removed, and leave behind the connected
scaffolding which is formed from the accessory germ; but this latter
has only _mechanical_ significance; the truly vital functions belong to
the other system.
105. The researches of modern histologists have all converged towards
the conclusion that the organs of Sense are modifications of the
surface, with epithelial cells which on the one side are connected with
terminal hairs, or other elements adapted to the reception of stimuli,
and are connected on the other side through nerve-fibres with the
perceptive centres. It has been shown that nerve-fibres often terminate
in (or among) epithelial cells--sensory fibres at the surface, and
motor-fibres in the glands.[132] Whether the fibres actually penetrate
the substance of the cell, or not, is still disputed. Enough for
our present purpose to understand that there is a _physiological_
connection between the two, and above all that sensory nerves are
normally stimulated through some epithelial structure or other.
[Illustration:
Fig. 15.--_Transverse section of a Blastoderm incubated for
eighteen hours._ The section passes through the medullary groove,
_m e_. A, epiblast. B, mesoblast. C, hypoblast. _m f_, medullary
fold, _c h_, notochord.
]
106. And this becomes clear when we go back to the earliest indications
of development. Look at Fig. 15, representing a transverse section of
the germinal membranes in a chick after eighteen hours’ incubation.
Here the three layers, A, B, and C, have the aspect of simple cells
very slightly differing among each other. Yet since each layer has
ultimately a progeny which is characteristically distinguishable, we
may speak of each not as what it now is, but what it will become.
Although the most expert embryologist is often unable to distinguish
the embryo of a reptile from that of a bird or of a mammal, at certain
stages of evolution, so closely does the one resemble the other, yet
inasmuch as the embryo of a reptile does not, cannot become a bird, nor
that of a bird a mammal, he is justified in looking forward to what
each will become, and in calling each embryo by its future name. On the
same ground, although we cannot point to any such distinction between
the layers of the blastoderm as I have indicated in the separation
of Instrumental and Alimental Systems, nor specify any characters by
which the cells can be recognized as epithelial, neural, and muscular,
yet a forward glance prefigures these divisions. We know that the
first result of the segmentation of the yolk is the formation of cells
all alike, which in turn grow and subdivide into other cells. We
know that these cells become variously modified both in composition
and structure, and that by such differentiations the simple organism
becomes a complex of organs.
107. But here it is needful to recall a consideration sometimes
disregarded, especially by those who speak of Differentiation as if
it were some magical Formative Principle, quite independent of the
state of the organized substance which is formed. There is a luminous
conception--first announced by Goethe, and subsequently developed by
Milne Edwards--which regards the organism as increasing in power and
complexity by a physiological “division of labor,” very similar to
that division of employments which characterizes the developed social
organism. But the metaphor has sometimes been misleading; it has been
interpreted as indicating that Function creates Organ (see PROBLEM I.
§ 88), and as if Differentiation itself were something more than the
expression of the changes resulting from the introduction of different
elements. In the Social Organism a “division of labor” presupposes
that laborers with their labor-materials are already existing; the
change is one of rearrangement: instead of each laborer employing
his skill in doing many kinds of work, he restricts it to one kind,
which he is then able to do with less loss of time and power. Thus is
social power multiplied without increase of population, and the social
organism becomes more complex by the differentiation of its organs. It
is not precisely thus with the Animal Organism during its evolution.
Indeed to suppose that the differentiation of the germinal membrane
into special tissues and organs takes place by any such division
of employments, is to fall into the ancient error of assuming the
organism to exist _preformed_ in the ovum. The unequivocal teaching of
Epigenesis is that each part is produced out of the elements furnished
by previous parts; and for every differentiation there must be a
difference in composition, structure, or texture--the first condition
being more important than the second, the second more important than
the third. The word protoplasm has almost as wide a generality as
the word animal, and is often used in forgetfulness of its specific
values: the protoplasm of a nerve-cell is not the _same_ as that of
a blood-cell, a muscle-cell, or a connective-tissue cell, any more
than a bee is a butterfly, or a prawn a lobster. No sooner has the
specific character been acquired, no sooner is one organite formed
by differentiation, than there is an absolute barrier against any
transformation of it into any other kind of organite. The nerve-cell,
muscle-cell, and epithelial cell have a common starting-point, and a
community of substance; but the one can no more be transformed into
the other than a mollusc can be transformed into a crustacean. In the
homogeneous cellular mass which subsequently becomes the “vertebral
plates,” a group of cells is very early differentiated: this is the
rudimentary spinal ganglion, which becomes enveloped in a membrane,
and then pursues a widely different course from that of the other
cells surrounding it, so that “the same cell which was formerly an
element of the vertebral plate now becomes a nerve-cell, while its
neighbors become cartilage-cells.”[133] Indeed all the hypotheses
of transformation of tissues by means of Differentiation are as
unscientific as the hypotheses of the transformation of animals. In the
organism, as in the Cosmos, typical forms once attained are retained.
There probably was a time in the history of the animal series when
masses of protoplasm by appropriating different materials from the
surrounding medium were differentiated into organisms more complex and
more powerful than any which existed before. But it is obvious that
from a common starting-point there could have been no variations in
development without the introduction of new elements of composition:
there might have been many modifications of structure, but unless
these facilitated modifications of composition, there could never have
resulted the striking differences observed in animal organisms.[134]
108. To return from this digression, we may liken the three primary
layers of the germinal membranes to the scattered and slightly
different masses of protoplasm out of which the animal kingdom
was developed. In this early stage there are no individualized
organites--no nerve-cells or muscle-cells. They are cells ready to
receive modifications both of composition and structure, appropriating
slightly different elements from the yolk, and according to such
appropriation acquiring different properties. And this is necessarily
so, since the different cells have not exactly the same relation to
the yolk, nor are they in exactly the same relation to the incident
forces which determine the molecular changes. The uppermost layer
(epiblast) under such variations develops into epithelium and central
nerve-tissue; the epithelial cell cannot develop into a nerve-cell, the
two organites are markedly unlike, yet both spring from a common root.
Another modification results in the development of muscle-cells from
the inner layer.
109. Hence we can understand how the surface is sensitive even
in organisms that are without nerve-tissue; and also how even in
the highest organisms there is an intimate blending of epithelial
with neural tissues. The same indication explains the existence
of neuro-muscular cells in the _Hydra_, recorded by Kleinenberg,
and of neuro-muscular fibres in the _Beroë_, by Eimer.[135] In the
simpler organisms the surface is at once protective, sensitive, and
absorbent. It shuts off the animal from the external medium, and thus
individualizes it; at the same time it connects this individual with
the medium; for it is the channel through which the medium acts, both
as food and stimulus. The first morphological change is one whereby
a part of the surface is bent inwards, and forms the lining of the
body’s cavity. Soon there follows such a modification of structure
between the outer and inner surfaces (_ectoderm_ and _endoderm_) that
the one is mainly sensitive and protective, the other mainly protective
and absorbent. The outer surface continues indeed to absorb, but its
part in this function is insignificant compared with that of the inner
surface, which not only absorbs but secretes fluids essential to
assimilation. The inner surface, although sensitive, is subjected to
less various stimulation, and its sensibility is more uniform.
110. The uppermost of the primary layers we have seen to be epithelial;
and we know that the first lines of the central nervous system are laid
there. A depression called the medullary groove is the first indication
of the future cerebro-spinal axis. Some writers--Kölliker, for
instance--regard this medullary groove as continuous with but different
from the epithelial layer; others maintain that it lies underneath the
epithelium, just as we see it in later stages, when the differentiation
between epithelial and nerve cell has taken place. Since no one
disputes the fact that when the groove becomes a closed canal its
lining is epithelial, one of two conclusions is inevitable: either
the cells of the primary layer develop in the two diverse directions,
epithelial and neural; or else epithelial cells can be developed on
the surface of neural cells and out of them. The latter conclusion is
one which, involving the conception of transformation, would seem to
be put out of court. I think, then, we must admit that the under side
of the primary layer of cells becomes differentiated into nerve-cells;
and this is in accordance with the observations of Messrs. Foster and
Balfour.[136]
111. While there is this intimate morphological and physiological
blending of epithelial and neural organites, there is an analogous
relation between neural and muscular organites. As the neural layer
lies under the epithelial, the muscular lies under the neural. The
surface stimulation passes to the centre, and is reflected on the
muscles. Embryology thus teaches why a stimulus from the external
medium must be propagated to a nerve-centre before it reaches the
muscles; and why a stimulus on one part of the surface may set all the
organism in movement, by passing through a centre which co-ordinates
all movements. This, of course, only applies to the higher organisms.
In the simpler structures the sensitive surface is directly continuous
with the motor organs.
It is unnecessary here to pursue this interesting branch of our
subject; nor need we follow the analogous evolution of the second
germinal membrane representing the Alimental System. Our attention
must be given to what is known and inferred respecting the elementary
structure of the nerves and centres, on which mainly the interest of
the psychologist settles, since to him the whole of Physiology is
merged in nerve actions.
CHAPTER VII.
THE ELEMENTARY STRUCTURE OF THE NERVOUS SYSTEM.
112. The progress of science involves an ever-increasing Analysis.
Investigation is more and more directed towards the separated details
of the phenomena previously studied as events; the observed facts
are resolved into their component factors, complex wholes into their
simpler elements, the organism into organs and tissues. But while the
analytical process is thus indispensable, it is, as I have often to
insist, beset with an attendant danger, namely, that in drawing the
attention away from one group of factors to fix it exclusively on
another, there is a tendency to forget this artifice, and instead of
restoring the factors provisionally left out of account, we attempt a
reconstruction in oblivion of these omitted factors. Hence, instead
of studying the properties of a tissue in all the elements of that
tissue, and the functions of an organ in the anatomical connections
of that organ, a single element of the tissue is made to replace the
whole, and very soon the function of the organ is assigned to this
particular element. The “superstition of the nerve-cell” is a striking
illustration. The cell has usurped the place of the tissue, and has
come to be credited with central functions; so that wherever anatomists
have detected ganglionic cells, physiologists have not hesitated
to place central functions. By such interpretations the heart and
intestines, the glands and blood-vessels, have, erroneously, I think,
their actions assigned to ganglionic cells.
It is unnecessary to point out the radical misconception which thus
vitiates a great mass of anatomical exposition and physiological
speculation. I only call the reader’s attention to the point at the
outset of the brief survey we have now to make of what is known
respecting the elementary structure of the nervous system.
DIFFICULTIES OF THE INVESTIGATION.
113. So great and manifold are the difficulties of the search, that
although hundreds of patient observers have during the last forty years
been incessantly occupied with the elementary structure of the nervous
system, very little has been finally established. Indeed, we may still
repeat Lotze’s sarcasm, that “microscopic theories have an average of
five years’ duration.” This need not damp our ardor, though it ought to
check a too precipitate confidence. Nothing at the present moment needs
more recognition by the student than that the statements confidently
repeated in text-books and monographs are very often for the most part
only ingenious guesses, in which Observation is to Imagination what
the bread was to the sack in Falstaff’s tavern bill. Medical men and
psychologists ought to be warned against founding theories of disease,
or of mental processes, on such very insecure bases; and physiological
students will do well to remember the large admixture of Hypothesis
which every description of the nervous system now contains. Not that
the potent aid of Hypothesis is to be undervalued; but its limits must
be defined. It may be used as a finger-post, not as a foundation. It
may suggest a direction in which truth may be sought; it cannot take
the place of Observation. It may link together scattered facts; it
must not take the place of a fact. We are glad of corks until we have
learned to swim. We are glad of a suggestion which will for the nonce
fill up the gaps left by observation, and hold the facts intelligibly
together. And both as suggestion and colligation, Hypothesis is
indispensable. Indeed, every _discovery_ is a verified hypothesis;
and there is no discovery until verification has been gained: up
to this point it was a guess, which might have been erroneous--a
torchbearer sent out to look for a missing child in one direction,
while the child was wandering in another; only when he finds the
child can we acknowledge that the torchbearer pursued the right path.
Hypothesis satisfies the intellectual need of an explanation, but we
must be wary lest we accept this fulfilment of a need as equivalent
to an enlargement of knowledge; we must not accept explanation as
demonstration, and suppose that because we can form a mental picture
of the possible stages of an event, therefore this picture represents
the actual stages. Let us be alert, forewarned against the tendency to
seek evidence in support of a conclusion, instead of seeking to unfold
the conclusion step by step from the evidence. To seek for evidence in
support of a _guess_ is very different from seeking it in support of
a _conclusion_; which latter practice is like that of people asking
advice, and only following it when it chimes in with their desires.
114. Is not the warning needed, when we find anatomists guided by
certain “physiological postulates,” and consequently _seeing_ only
what these postulates demand? For example, there is the postulate of
“isolated conduction,” which is said to require that every nerve-fibre
should pursue its course singly from centre to periphery. Accordingly
the fibres are described as unbranched. Whatever may be the demand
of the postulate, or the felt necessity of the deduction, the fact
is that nerve-fibres do branch off during their course at various
points; nay, it is doubtful whether any lengthy fibre is unbranched.
Other postulates demand what fact plainly denies. It is said to be
“necessary” that every cell should have at least two fibres, and that
sensory and motor nerves should be directly connected through their
respective cells. These things cannot be seen, but they are described
with unhesitating precision. Diagrams are published in which the
sensory fibres pass into the cells of the posterior horn of the spinal
cord, and these cells send off prolongations to the cells of the
anterior horn, and thence the motor fibres pass out to the muscles:
an absolutely impossible arrangement, according to our present data!
Again, the postulate that nerve-force originates in the cells, and that
nerve-functions depend on cells, required that the cells should be most
abundant where the function was most energetic. Of course they were
found most abundant in the required places--no notice whatever being
taken of the facts which directly contradicted the deduction.
115. Among the serious obstacles to research we must reckon this
tendency to substitute Imaginary Anatomy for Objective Anatomy. I am
conscious of the tendency in myself, as I note it in others; and have
constantly to struggle against it, though not perhaps always aware of
it. Many a time have I had to relinquish plausible explanations, which
would have supported my speculations could I but have believed that
they represented the facts; but being unable to believe this, I had to
remember that hypotheses and explanations appear and disappear--only
the solid fact lives. If there is one lesson emphatically taught by
Philosophy, it is the unwisdom of founding our conclusions on our
desires rather than on the objective facts.
116. In the following pages a constantly critical attitude is
preserved: this is simply to keep active the sense of how much is still
needed to be done before a satisfactory theory of the nervous system
can be worked out. The objective difficulties are greater than in any
other department of Anatomy. The problem is to form a precise picture
of what the organites are, and of how they are arranged in the living
tissue; yet our present means of investigation involve as a preliminary
that we should _alter_ that arrangement, _removing_ some elements of
the tissue, and _changing_ the state of others, without knowing what
were their precise state and arrangement before the change. Place a
piece of nerve-tissue under the microscope, without having subjected
it to various mechanical and chemical operations, and you can see next
to nothing of its structure. You must tear the parts asunder, and
remove the fat and nerve-sap (plasmode) before you can see anything;
you must coagulate the albumen, and otherwise chemically alter the
substances before a thin section can be made; you must get rid of
the tissues in which it is embedded, without knowing what are the
connections thus destroyed. Living neurine has no greater consistence
than cream, often no greater than oil. How, then, can thin sections
be made until this viscid substance has been hardened by alcohol or
acids? But substances thus acted on lose their constituent water,
which can no more be removed without alteration of their structure,
than it can be removed from certain salts without destruction of their
special properties. Losing their water alone, they become deformed.
They lose much more. Sometimes the loss can be estimated, as in the
case of the hyaline substance investing the nucleus during the process
of segmentation in embryonic cells, which may be seen to disappear when
a weak solution of acid is applied.[137] At other times we are unable
to say what has disappeared. Under different modes of preparation very
different appearances are observed, and anatomists are accordingly at
variance. Yet unless some hardening method be adopted little can be
seen! Stilling, who has given his life to the study, declares that no
results are reliable which are obtained from the unprepared tissue,
because the mechanical isolation of the elements destroys the textural
arrangement.[138] There is one method of hardening, and only one, which
we can be certain does not chemically alter the structure, and that
is the freezing method. The experiments of Dr. Weir Mitchell and Dr.
Richardson prove this, because they prove that the brain of the living
animal may be frozen and frozen again and again, yet recover its vital
activity when thawed. Professor Rutherford has invented an admirable
instrument for making sections of the frozen tissue, of any delicacy
that may be required; but with the thinnest section there will still be
certain difficulties of observation, unless the tissue has undergone a
staining process. Whatever is seen, however, in the frozen tissue is to
be accepted as normal.
117. Two points must be determined before reliance can be placed on
observations of tissues chemically acted on: First, we must prove that
the forms now visible existed before the preparation--the chemical
action merely unveiling them; secondly, we must estimate the part
played by the elements which have been removed in order to make the
rest visible. We know, for example, that the nucleus often exists in
the cell, though an acid may be needed to make it visible. We also
know that cells which during life are quite free from visible granules
are distinctly granulated after death, even without external chemical
action. Imagine the explanation of a steam-engine to be attempted by
first taking it to pieces, and examining these pieces, with no account
of the coals and steam which had previously been _removed_ in order to
facilitate the examination. When we know the part played by coals and
steam, we may disregard these items of the active machine. So when we
know the part played by water, fat, amorphous substance, and plasmode,
we may describe nerve-tissue without taking these into account.
118. “You have convinced me,” said Rasselas to Imlac, “that it is
impossible to be a poet.” My readers may, perhaps, infer from this
enumeration of the difficulties that a knowledge of the minute anatomy
of the nervous system is impossible. Not so; but a knowledge of these
difficulties should impress us with the necessity for a vigilant
scepticism, and the search after new methods. If the difficulties
are fairly faced, they may be finally overcome. What we must resign
ourselves to at present is the conviction that our knowledge is not
sufficiently accurate to be employed as a basis of deduction in the
explanation of physiological and psychological processes.[139]
119. Having said so much, let me add that there are some positive
materials, and these yearly receive additions. The organites are
described with a general agreement as to their composition and
structure--although there is much that is hypothetical even here.
Neurine is known under two aspects: the amorphous and the figured. The
figured, which is the better known, comprises cells of different kinds,
fibres and fibrils. The amorphous, more generally called _Neuroglia_,
or nerve-cement, is less understood, and is indeed by many authorities
excluded altogether from the nerve-tissue proper, and relegated to the
class of connective tissues.
THE NERVE-CELL.
120. It is unfortunate that the term nerve-cell is applied to organites
of very variable structure. Nerve-cell is a generic term of which
the species are many; under it are designated organites in different
stages--as infancy, childhood, and manhood are all included under Man.
Most commonly by nerve-cell is understood the ganglionic corpuscle,
conspicuous in its size and its prolongations, such as it appears in
the great centres, and in ganglia. It also designates smaller different
organites, sometimes called “nuclei” (_Kerne_), sometimes grains
(_Körner_). There would be advantage in designating the earlier stages
as _neuroblasts_, reserving the word _cells_ for the more developed
forms. Such a distinction would facilitate the discussion of whether
nerve-fibres had or had not their origin in cells; because while I, for
one, see very coercive evidence against the accepted notion that all
the fibres have their origin in the processes of ganglionic corpuscles,
I see no reason to doubt that both fibres and corpuscles have their
origin in neuroblasts. Of this anon.
The cell is a composite organite, the primary element being a
microscopic mass of protoplasm, or what may more conveniently be
termed _neuroplasm_. It appears as finely granulated and striated
or fibrillated substance on a hyaline ground, with water, fat, and
diffused pigment in varying quantities. The cell contains a nucleus,
and nucleolus--sometimes two. Like other animal cells, it sometimes has
a distinct cell-wall, sometimes not. Its size and shape are variable:
sometimes distinctly visible to the naked eye, generally visible only
under the microscope.[140] It is round, oval, pyramidal, club-shaped,
pear-shaped, or many-cornered. It has one, two, three, or many
outgrowths called “processes,” and according to the processes it is
known as unipolar, bipolar, and multipolar. When there are no processes
the cell is called apolar. Some idea of these processes may be formed
if they are likened to the pseudopodia of Amœbæ and Foraminifera.
Compare Fig. 16, a nerve-cell, figured by Gerlach, with Fig. 17, one
highly magnified, in which Max Schultze’s hypothesis is represented.
[Illustration:
Fig. 16.--_Nerve-cell from anterior horn of spinal cord (man),
magnified 150 diameters._ _a_, cell process unbranched passing into
or joining an axis cylinder, the other processes are branched; _b_,
pigment. The nucleus and nucleolus are visible.
]
[Illustration: Fig. 17.--_Nerve-cell from the anterior gray substance
of the spinal cord of a calf magnified 600._ _a_, the axis cylinder;
_b_, the branched process. The neuroplasm is represented as distinctly
fibrillated, with granular substance interspersed. Nucleus and
nucleolus very distinct.]
121. Such is a general description of the nerve-cell as it is seen in
various places, and under various modes of preparation. How much is
due to preparation we cannot positively say. While we always discover
fibrine in the blood after it is withdrawn from the vessels, we know
that fibrine as such does not exist in the circulating blood. And if
neurine is a semi-liquid substance, we may doubt whether in the living
cell it is fibrillated. Doubts have been thrown even on the normal
existence of the granular substance, which has been attributed to
coagulation. Thus we know that the nucleus of the white blood-corpuscle
appears perfectly homogeneous until subjected to heat, yet at a certain
temperature (86° F.) it assumes the aspect of a fine network. Haeckel
observed the hyaline substance of the neurine in crayfish become
troubled and changed directly any fluid except its own blood-serum
came in contact with it. Leydig noticed the transparent ganglion of a
living Daphnia become darker and darker as the animal died; and I saw
something like this, after prolonged struggles of a Daphnia to escape
from a thread in which its leg was entangled. Charles Robin, indeed,
asserts that the passage from the hyaline to the finely granulated
state is a characteristic of the dying cell.[141] On the other hand,
it should be noted that Max Schultze describes a fibrillated appearance
in cells just removed from the living animal, and placed in serum.
When, therefore, one observer describes the neuroplasm as being clear
as water, another as finely granular, and a third as fibrillated,
we must conclude that the observations refer to cells, 1°, under
different states of vitalization, or, 2°, under different modes of
preparation. On the first head we note that some nerve-cells are so
perishable that Trinchese declares he could find no cells in the
ganglia of a cuttlefish which had been dead twenty-four hours, although
they were abundant in one recently killed.[142] On the second head
we note that the changes wrought by modes of preparation cannot be
left out of consideration. Auerbach notices that the cells and fibres
apparent in the _plexus myentericus_ after an acid has been applied,
cannot be detected before that application--nothing is visible but a
pale gelatinous network, with here and there knots of a paler hue;
and I remember my surprise on examining the fresh spinal cord of a
duck-embryo, and finding no trace of cells such as I had that very
morning seen in the cord of a chick of earlier date, but which had been
soaked in weak bichromate of potash. Now we have excellent grounds for
believing that in both cases these organites were present, and that it
was the reagent which disclosed their presence in the chick; and so in
other cases we must ask whether the forms which appear under a given
mode of preparation are simply _unmasked_, or are in truth _produced_
by the reagent? This question we can rarely answer.
If one of the very large cells be taken from the ganglion of a living
mollusc, and be gently pressed till it bursts, the discharged contents
will be seen to be of a hyaline viscid substance, with fine granules
but no trace of fibres. Yet we must not rashly generalize from this,
and declare that in the vertebrate cells the substance is not also
fibrillated. As a good deal of speculation rests on the assumption of
the fibrillated cell-contents, I have thought it worth while to note
the uncertainty which hovers round it.
122. Among the uncertainties must be reckoned the question as to the
cell-processes. The existence of apolar and unipolar cells is flatly
denied by many writers, who assert that the appearances are due to the
fragility of the processes. Fragile the processes are, and evidence
of their having been broken off meet us in every preparation; but the
denial of apolar and unipolar cells seems to me only an example of
the tendency to substitute hypothesis for observation (§ 114). The
“postulate” which some seem to regard as a “necessity of thought” that
every nerve-cell shall have at least two fibres, one ingoing, the other
outgoing, is allowed to override the plain evidence.[143] It originated
in the fact first noticed by Wagner and Charles Robin that certain
cells in the spinal ganglia of fishes are bipolar. The fact was rapidly
generalized, in spite of its not being verified in _other_ places; the
generalization was accepted because (by a strange process of reasoning
running counter to all physiological knowledge) it was thought to
furnish an elementary illustration of the reflex process. As the centre
had its ingoing and outgoing nerve, so the cell was held to be a centre
“writ small,” and required its two fibres, No one paused to ask, how a
cell placed in the _track_ of an ingoing nerve could fulfil this office
of a reflex centre; no one supposed that the portion of the sensory
fibre which continued its course, after the interruption of the cell,
was a motor fibre.
What does Observation teach? It teaches that at first all nerve-cells
are apolar. Even in the cortex of the cerebrum, where (unless we
include the nuclei and grain-like corpuscles under cells) all the cells
are finally multipolar, there is not one which has a process, up to
the seventh or eighth day of incubation (in the chick); from that day,
and onwards, cells with one process appear; later on, cells with two,
and later still, with three. By this time all the apolar cells have
disappeared. They may therefore be regarded as cells in their infancy.
However that may be, we must accept the fact that apolar cells exist;
whether they can co-operate in neural functions, is a question which
must be decided after the mode of operation of cells is placed beyond a
doubt.
123. If apolar cells are embryonic forms of cells which afterwards
become multipolar, this interpretation will not suffice for the
unipolar cells. They are not only abundant, but are mature forms in
some organs, and in some animals; though in some organs they may truly
be regarded as embryonic. Thus in the human embryo up to the fourth
month all the cells of the spinal cord are said to be unipolar,[144]
later on they become multipolar. But in birds, rabbits, dogs, and
even man, the cells in the spinal ganglia are mainly (if not wholly)
unipolar;[145] nor is there any difficulty in observing the same fact
in the œsophageal ganglia of molluscs (see Fig. 22).
Such are the observations. They have indeed been forced into agreement
with the bipolar postulate, by the assumption that the single process
branches into two, one afferent, the other efferent.[146] But before
making observation thus pliant to suit hypothesis, it would be well to
look more closely into the evidence for the hypothesis itself. For my
own part, I fail to see the justification of the postulate; whereas
the existence of unipolar cells is an observation which has been amply
verified.
[Illustration: Fig. 18.--_Supposed union of two nerve-cells and a
fibre._ The processes subdivide into a minute network, in which the
fibre also loses itself.]
124. Bipolar cells abound; multipolar cells are still more abundant;
and these are the cells found in the gray substance of the neural
axis. Deiters, in his epoch-making work,[147] propounded an hypothetic
_schema_ which has been widely accepted. Finding that the large
cells in the anterior horn of the spinal cord gave off processes
of different kinds, one branched, the other unbranched, he held
that the latter process was the origin of the axis cylinder of
a nerve-fibre, whereas the branched process was protoplasm which
divided and subdivided, and formed the connection between one cell
and another. Gerlach has modified this by supposing that the minute
fibrils of the branching process reunite and form an axis cylinder
(Fig. 18). There is no doubt that some processes terminate in a fine
network; and there is a probability (not more) that the unbranched
process is always continuous with the axis cylinder of a motor nerve,
as we know it sometimes is with that of a dark-bordered fibre in the
white substances. This, though probable, is, however, very far from
having been demonstrated. Once or twice Kölliker, Max Schultze, and
Gerlach have followed this unbranched process as far as the _root_ of
a motor nerve; and they infer that although it could not be traced
further, yet it did really join an axis cylinder there. In support
Of this inference came the observations of Koschennikoff,[148] that
in the cerebrum and cerebellum, processes were twice seen continuous
with dark-bordered nerve-fibres. But the extreme rarity of such
observations amid thousands of cells is itself a ground for hesitation
in accepting a generalized interpretation, the more so since we have
Henle’s observation of the similar entrance of a _branched_ process
into the root.[149] Now it must be remembered that the branched process
is by no anatomist at present regarded as the origin of the axis
cylinder; so that if it can enter the root without being the origin of
a nerve-fibre, we are not entitled to assume that the entrance of the
unbranched process has any other significance (on this head compare
§ 145), especially when we reflect that no trustworthy observer now
professes to have followed a nerve-fibre of the posterior root right
into a multipolar cell. Figures, indeed, have been published which
show this, and much else; but such figures are diagrams, not copies of
what is seen. They belong to Imaginary Anatomy.[150] The relation of
the cell-process to the nerve-fibre will be discussed anon.
[Illustration:
Fig. 19.--_Anastomosing nerve-cells_ (after Gratiolet). _a_, body
of the cell; _c_, process of uniting two cells; _d_, branching
process.
]
125. A word in passing on the contradictory assertions respecting
the anastomosis of nerve-cells. That the gray substance forms a
_continuum_ of some kind is certain from the continuity of propagation
of a stimulus. But it is by no means certain that one cell is directly
united to its neighbor by a cell-process. Eminent authorities assert
that such direct union never takes place; others, that it is a rare
and insignificant fact; others, that it is constant, and “demanded by
physiological postulates.” I will not, in the presence of distinct
affirmations, venture to deny that such appearances as are presented
in Fig. 19 may occasionally be observed; the more so as I have myself
seen perhaps half a dozen somewhat similar cases; but it is the opinion
of Deiters and Kölliker that all such appearances are illusory.[151]
Granting that such connections occur, we cannot grant this to be
the normal mode; especially now the more probable supposition is
that the connection is normally established by means of the delicate
ramifications of the branching processes.
Imaginary Anatomy has not been content with the cells of the anterior
horn being thus united together, to admit of united action, but has
gone further, and supposed that the cells of the posterior horn,
besides being thus united, send off processes which unite them with
the cells of the anterior horn--and thus a pathway is formed for
the transmission of a sensory impression, and its conversion into a
motor impulse. What will the reader say when informed that not only
has no eye ever beheld such a pathway, but that the first step--the
direct union of the sensory nerve-fibre with a cell in the _posterior_
horn--is confessedly not visible?
126. The foregoing criticisms will perhaps disturb the reader who has
been accustomed to theorize on the data given in text-books; but he
may henceforward be more cautious in accepting such data as premises
for deduction, and will look with suspicion on the many theories which
have arisen on so unstable a basis. When we reflect how completely
the modern views of the nervous system, and the physiological,
pathological, and psychological explanations based on these views,
are dominated by the current notions of the nerve-cell, it is of the
last importance that we should fairly face the fact that at present
our knowledge even of the structure of the nerve-cell is extremely
imperfect; and our knowledge of the part it plays--its anatomical
relations and its functional relations--is little more than guesswork!
THE NERVES.
127. We now pass to the second order of organites; and here our
exposition will be less troubled by hesitations, for although there is
still much to be learned about the structure and connections of the
nerve-fibres, there is also a solid foundation of accurate knowledge.
[Illustration:
Fig. 20.--_a_, axis cylinder formed by the fibrils of the cell
contents, and at _a’_ assuming the medullary sheath; _b_, naked
axis cylinder from spinal cord.
]
A nerve is a bundle of fibres within a membranous envelope supplied
with blood-vessels. Each fibre has also its separate sheath, having
annular constrictions at various intervals. It is more correctly named
by many French anatomists a nerve-_tube_ rather than a nerve-_fibre_;
but if we continue to use the term _fibre_, we must reserve it for
those organites which have a membranous sheath, and thereby distinguish
it from the more delicate _fibril_ which has none.
The nerve tube or fibre is thus constituted: within the sheath
lies a central band of neuroplasm identical with the neuroplasm of
nerve-cells, and known as the _axis cylinder_; surrounding this band
is an envelope of whitish substance, variously styled _myeline_,
_medullary sheath_, and _white substance of Schwann_: it is closely
similar to the chief constituent of the yolk of egg, and to its
presence is due the whitish color of the fibres, which in its absence
are grayish. The axis cylinder must be understood as the primary and
essential element, because not only are there nerve-fibrils destitute
both of sheath and myeline yet fulfilling the office of Neurility,
but at their terminations, both in centres and in muscles, the
nerve-fibres always lose sheath and myeline, to preserve only the
neuroplasmic threads of which the axis cylinder is said to be composed.
In the lowest fishes, in the invertebrates, and in the so-called
sympathetic fibres of vertebrates, there is either no myeline, or it is
not separated from the neuroplasm.
128. Nerve-fibres are of two kinds--1°. The _dark-bordered_ or
_medullary_ fibres, which have both sheath and myeline, as in the
peripheral system; or only myeline, without the sheath, as in the
central system. 2°. The _non-medullary_ fibres, which have the sheath,
without appreciable myeline--such are the fibres of the olfactory, and
the pale fibres of the sympathetic.
Nerve-fibrils are neuroplasmic threads of extreme delicacy, visible
only under high magnifying powers (700–800), which abound in the
centres, where they form networks. The fibrils also form the
terminations of the fibres. Many fibrils are supposed to be condensed
in one axis cylinder. This is represented by Max Schultze in Figs. 17
and 20.
129. As may readily be imagined, the semi-liquid nature of the
neuroplasm throws almost insuperable difficulties in the way of
accurately determining whether the axis cylinder in the living nerve
is fibrillated or not; whether, indeed, any of the aspects it presents
in our preparations are normal. Authorities are not even agreed as
to whether it is a pre-existent solid band of homogeneous substance,
or a bundle of primitive fibrils, or a product of coagulation.[152]
Rudanowsky’s observations on frozen nerves convinced him that the
cylinder is a tubule with liquid contents.[153] My own investigations
of the nerves of insects and molluscs incline me to the view of Dr.
Schmidt of New Orleans, namely, that the cylinder axis consists
of minute granules arranged in rows and united by a homogeneous
interfibrillar substance, thus forming a bundle of granular fibrils
enclosed in a delicate sheath[154]--in other words, a streak of
neuroplasm which has a fibrillar disposition of its granules. We ought
to expect great varieties in such streaks of neuroplasm; and it is
quite conceivable that in the Rays and the Torpedo there are axis
cylinders which are single fibrils, and others which are bundles, with
finely granulated interfibrillar substance.[155]
The fibres often present a varicose aspect, as represented in Fig. 21.
It is, however, so rarely observed in the fresh tissue, that many
writers regard it (as well as the double contour) as the product of
preparation.[156] It is, indeed, always visible after the application
of water.
We need say no more at present respecting the structure of
nerve-fibres, except to point out that we have here an organite not
less complex than the cell.
[Illustration:
Fig. 21.--_Nerve-fibres from the white substance of the cerebrum._
_a_, _a_, _a_, the medullar contents pressed out of the tube as
irregular drops.
]
THE NEUROGLIA.
130. Besides cells and fibres, there is the _amorphous substance_,
which constitutes a great part of the central tissue, and also enters
largely into the peripheral tissue. It consists of finely granular
substance, and a network of excessively delicate fibrils, with nuclei
interspersed. Its character is at present _sub judice_. Some writers
hold it to be nervous, the majority hold it to be simply one of
the many forms of connective tissue: hence its name neuroglia, or
nerve-cement.
In the convolutions of the frozen brain Walther finds the cells and
fibres imbedded in a structureless semi-fluid substance wholly free
from granules; the granules only appear there when cells have been
crushed. It is to this substance he attributes the fluctuation of
the living brain under the touch, like that of a mature abscess; the
solidity which is felt after death is due to the coagulation of this
substance. Unhappily we have no means of determining whether the
network visible under other modes of investigation is present, although
invisible, in this substance. The neuroglia, as it appears in hardened
tissues, must therefore be described with this doubt in our minds.
If we examine a bit of central gray substance where the cells and
fibres are sparse, we see, under a low power, a network of fibrils
in the meshes of which lie nerve-cells. Under very high powers we
see outside these cells another network of excessively fine fibrils
embedded in a granular ground substance, having somewhat the aspect of
hoar-frost, according to Boll. It is supposed that the first network
is formed by the ultimate ramifications of the nerve-cell processes,
and that the second is formed by ramifications of the processes of
_connective_ cells. In this granular, gelatinous, fibrillar substance
nuclei appear, together with small multipolar cells not distinguishable
from nerve-cells except in being so much smaller. These nuclei are
more abundant in the tissue of young animals, and more abundant in the
cerebellum than in the cerebrum. The granular aspect predominates the
fresher the specimen, though there is always a network of fibrils; so
that some regard the granules as the result of a resolution of the
fibrils, others regard the fibrils as the linear crystallization (so to
speak) of the granules.[157]
131. Such is the aspect of the neuroglia. I dare not venture to
formulate an opinion on the histological question whether this
amorphous substance is neural, or partly neural and partly connective
(a substance which is potentially both, according to Deiters and
Henle), or wholly connective. The question is not at present to be
answered decisively, because what is known as connective tissue has
also the three forms of multipolar cells, fibrils, and amorphous
substance; nor is there any decisive mark by which these elements in
the one can be distinguished from elements in the other. The physical
and chemical composition of Neuroglia and Neuroplasm are as closely
allied as their morphological structure. And although in the later
stages of development the two tissues are markedly distinguishable,
in the early stages every effort has failed to furnish a decisive
indication.[158] Connective tissue is dissolved by solutions which
leave nerve-tissue intact. Can we employ this as a decisive test? No,
for if we soak a section of the spinal cord in one of these solutions,
the _pia mater_ and the membranous septa which ramify from it between
the cells and fibres disappear, leaving all the rest unaltered. This
proves that Neuroglia is at any rate chemically different from ordinary
connective tissue, and more allied to the nervous. As to the _staining_
process, so much relied on, nothing requires greater caution in its
employment. Stieda found that the same parts were sometimes stained and
sometimes not; and Mauthner observed that in some cells both contents
and nucleolus were stained, while the nucleus remained clear, in other
cells the contents remained clear; and some of the axis cylinders were
stained, the others not.[159] Lister found that the connective tissue
between the fibres of the sciatic nerve, as well as the _pia mater_,
were stained like the axis cylinders;[160] and in one of my notes there
is the record of both (supposed) connective cells and nerve-cells being
stained alike, while the nerve-fibres and the (supposed) connective
fibres were unstained. Whence I conclude that the supposition as to
the nature of the one group being different from that of the other was
untenable, if the staining test is to be held decisive.
132. The histological question is raised into undue importance because
it is supposed to carry with it physiological consequences which would
deprive the neuroglia of active co-operation in neural processes,
reducing it to the insignificant position of a mechanical support. I
cannot but regard this as due to the mistaken tendency of analytical
interpretation, which somewhat arbitrarily fastens on one element in a
complex of elements, and assigns that one as the sole agent. Whether
we call the neuroglia connective or neural, it plays an essential part
in all neural processes, probably a more important part than even the
nerve-cells, which usurp exclusive attention! To overlook it, or to
assign it a merely _mechanical_ office, seems to me as unphysiological
as to overlook blood-serum, and recognize the corpuscles as the only
nutrient elements. The notion of the neuroglia being a mere vehicle of
support for the blood-vessels arises from not distinguishing between
the alimental and instrumental offices. In the function of a limb, bone
is a co-operant. In the function of a centre, connective tissue is a
co-operant; so that even if we acknowledge neuroglia to be a special
form of connective tissue, it is an agent in neural processes; _what_
its agency is, will be hereafter considered.
Following Bidder and Kupffer, the Dorpat school proclaimed the whole
of the gray substance of the posterior half of the spinal cord to
be connective tissue; and Blessig maintained that the whole of the
retina, except the optic fibres, was connective tissue.[161] Even those
anatomists who regarded this as exaggerated, admitted that connective
tissue largely enters into the gray substance, especially if the
granular ground substance be reckoned as connective, the nerve-cells
being very sparse in the posterior region. Be it so. Let us admit
that the gray matter of the frog’s spinal cord is mainly composed of
neuroglia, in which a very few multipolar nerve-cells are embedded.
What must our conclusion be? Why, that since this spinal cord is
proved to be a centre of energetic and manifold reflex actions--even
to the extent of forcing many investigators to attribute sensation and
volition to it--this is proof that connective tissue does the work of
nerve-tissue, and that the neuroglia is more important than nerve-cells!
Three hypotheses are maintainable--1°. The neuroglia is the amorphous
ground-substance of undeveloped tissue (neuroplasm) out of which the
cells and fibres of nerve-tissue and connective tissue are evolved.
2°. It is the product of dissolved nerve cells and fibres. 3°. It is
the undeveloped stage of connective tissue. For physiological purposes
we may adopt any one of these views, provided we keep firm hold of the
fact that the neuroglia is an essential element, and in the centres a
dominant element. To make this clear, however, we must inquire more
closely into the relations of the three elements, nerve-cells, fibres,
and neuroglia.
THE RELATIONS OF THE ORGANITES.
133. In enumerating among the obstacles to research the tendency to
substitute hypothetic deductions in place of objective facts, I had
specially in my mind the wide-reaching influence of the reigning
theories of the nerve-cell. Had we a solidly established theory of the
cell, equivalent, say, to our theory of gas-pressure, we should still
need caution in allowing it to override exact observation; but insecure
as our data are, and hypothetical as are the inferences respecting
the part played by the cell, the reliance placed on deductions from
such premises is nothing less than superstition. Science will take a
new start when the whole question is reinvestigated on a preliminary
setting aside of all that has been precipitately accepted respecting
the office of the cell. This exercise of the imagination, even should
the reigning theories subsequently be confirmed, would not fail to
bring many neglected facts into their rightful place.
I am old enough to remember when the cell held a very subordinate
position in Neurology, and now my meditations have led me to return, if
not to the old views of the cell, at least to something like the old
estimate of its relative importance. Its existence was first brought
prominently forward by Ehrenberg in 1834, who described its presence in
the sympathetic ganglia; and by Remak in 1837, who described it in the
spinal ganglia. For some time afterwards the ganglia and centres were
said to contain irregular masses of vesicular matter which were looked
on as investing the fibres; what their office was, did not appear. But
there rapidly arose the belief that the cells were minute batteries
in which “nerve-force” was developed, the fibres serving merely as
conductors. Once started on this track, Hypothesis had free way, and a
sort of fetichistic deification of the cell invested it with miraculous
powers. In many works of repute we meet with statements which may
fitly take their place beside the equally grave statements made by
savages respecting the hidden virtues of sticks and stones. We find
the nerve-cells credited with “metabolic powers,” which enable them
to “spiritualize impressions, and materialize ideas,” to _transform_
sensations into movements, and _elaborate_ sensations into thoughts;
not only have they this “remarkable aptitude of metabolic local
action,” they can also “act at a distance.”[162] The savage believes
that one pebble will cure diseases, and another render him victorious
in war; and there are physiologists who believe that one nerve-cell has
sensibility, another motricity, a third instinct, a fourth emotion, a
fifth reflexion: they do not say this in so many words, but they assign
to cells which differ only in size and shape, specific qualities. They
describe sensational, emotional, ideational, sympathetic, reflex, and
motor-cells; nay, Schröder van der Kolk goes so far as to specify
hunger-cells and thirst-cells.[163] With what grace can these writers
laugh at Scholasticism?
134. The hypothesis of the nerve-cell as the fountain of nerve-force
is supported by the gratuitous hypothesis of cell-substance having
greater chemical tension and molecular instability than nerve-fibre.
No evidence has been furnished for this; indeed the only experimental
evidence bearing on this point, if it has any force, seems directly
adverse to the hypothesis. I allude to the experiments of Wundt, which
show that the faint stimulus capable of moving a muscle when applied
directly to its nerve, must be increased if the excitation has to pass
through the cells by stimulation of the sensory nerve.[164] Wundt
interprets this as proving that the cells retard every impulse, whereby
they are enabled to store up latent force. The cells have thus the
office of locks in a canal, which cause the shallow stream to deepen at
particular places. I do not regard this interpretation as satisfactory;
but the fact at any rate seems to prove that so far from the cells
manifesting greater instability than the fibres, they manifest less.
135. The hypothesis of nerve-force being developed in the ganglia,
gradually assumed a more precise expression when the nerve-cells were
regarded as the only important elements of a ganglion. It has become
the foundation-stone of Neurology, therefore very particular care
should be taken to make sure that this foundation rests on clear and
indisputable evidence. Instead of that, there is absolutely no evidence
on which it can rest; and there is much evidence decidedly opposed to
it. Neither structure nor experiment points out the cells as the chief
agents in neural processes. Let us consider these.
Fig. 22 shows the contents of a molluscan ganglion which has been
teased out with needles.
[Illustration: Fig. 22.--_Cells, fibres, and amorphous substance from
the ganglion of a mollusc_ (after Bucholtz).]
The cells are seen to vary in size, but in all there is a rim of
neuroplasm surrounding the large nucleus, and from this neuroplasm
the fibre is seen to be a prolongation. The dotted substance in the
centre is the neuroglia. Except in the possession of a nucleus, there
is obviously here no essential difference in the structure of cell and
fibre.
[Illustration:
Fig. 23--_Fibres from the auditory nerve._ _a_, the axis cylinder;
_b_, the cellular enlargement; _c_, the medullary sheath.
]
Now compare this with Fig. 23, representing three fibres from the
auditory nerve.
Here the cell substance, as Max Schultze remarks, “is a continuation
of the axis cylinder, and encloses the nucleus. The medulla commonly
ceases at the point where the axis enters the cell, to reappear at its
exit; but it sometimes stretches across the cell to enclose it also:
so that such a ganglion cell is in truth simply the nucleated portion
of the cylinder axis.”[165] There are many places in which fibres are
thus found with cells inserted in their course as swellings: in the
spinal ganglia of fishes these are called bipolar cells; they are
sometimes met with even in the cerebellum; but oftener in peripheral
nerves, where they are mostly small masses of granular neuroplasm
from which usually a branching of the fibre takes place. The point
to which attention is called is that in some cases, if not in all,
the nerve-fibre is structurally continuous with the cell contents.
The two organites--fibre and cell--differ only as regards the nucleus
and pigment. Haeckel, who affirms that in the crayfish (_Astacus
fluviatilis_) he never saw a cell which did not continue as a fibre,
thinks there is always a marked separation of the granular substance
from its “hyaline protoplasm,” and that only this latter forms the axis
cylinder. But although my observations agree with this as a general
fact, I have seen even in crayfish the granular substance prolonged
into the axis cylinder; and in other animals the granular substance is
frequently discernible.
Indeed it may be said that anatomists are now tolerably unanimous as to
the axis cylinder being identical with the protoplasmic cell substance.
If this be so, we have only to recall the principle of identity of
property accompanying identity of structure, to conclude that _whatever
properties we assign to the cells_ (unless we restrict these to the
nucleus and pigment) _we must assign to the axis cylinders_. We can
therefore no longer entertain the hypothesis of the cells being the
fountains or reservoirs of Neurility; the less so when we reflect that
cells do not form the hundredth part of nerve-tissue: for even the
gray substance bears but a small proportion to the white; and of the
gray substance, Henle estimates that one half is fibrous, the rest is
partly cellular, partly amorphous. Those who derive Neurility from
the cells, forget that although the organism begins as a cell, and
for some weeks consists mainly of cells, yet from this time onwards
there is an ever-increasing preponderance of cell-derivatives--fibres,
tubes, and amorphous substance--and corresponding with this is the
ever-increasing power and complexity of the organism.
136. From another point of view we must reject the hypothesis. Not
only does the evidence which points to the essential continuity in
structure of nerve cell and fibre discredit the notion of their
physiological diversity, but it is further supported by the fact
that although the whole nervous system is structurally continuous,
an immense mass of nerve-fibres have no _immediate_ connection with
ganglionic cells:--neither springing from nor terminating in such
cells, their activity cannot be assigned to them. To many readers this
statement will be startling. They have been so accustomed to hear
that every fibre begins or terminates in a cell, that a doubt thrown
on it will sound paradoxical. But there is an equivoque here which
must be got rid of. When it is said that every fibre has its “origin”
in a cell, this may be true if origin mean its _point of departure
in evolution_, for “cells” are the early forms of all organites;
but although every organite is at first a cell, and in this sense a
nerve-fibre must be said to originate in a cell, we must guard against
the equivoque which arises from calling the highly differentiated
organite, usually designated ganglionic cell, by the same name as
its starting-point. On this ground I suggest the term neuroblast, in
lieu of nerve-cell, for the earlier stages in the evolution of cell
and fibre. Both Embryology and Anatomy seem to show that cell and
fibre are organites differentiated from identical neuroblasts, with a
somewhat varying history, so that in their final stages the cell and
fibre have conspicuous differences in form with an underlying identity;
just as a male and female organism starting from identical ova, and
having essential characters in common, are yet in other characters
conspicuously unlike. The multipolar cell is not necessarily the origin
of a nerve-fibre, although it is probable that some short fibres
have their origin in the prolongations of cells. Although the latter
point has not, I think, been satisfactorily established, except in the
invertebrata, I see no reason whatever to doubt its probability; what
seems the least reconcilable with the evidence is the notion that all
fibres arise as prolongations from ganglionic cells, instead of arising
independently as differentiations from neuroblasts. The reader will
observe that my objection to the current view is purely anatomical; for
the current view would suit my physiological interpretations equally
well, and would be equally irreconcilable with the hypothesis of the
cell as the source of Neurility, so long as the identity of structure
in the axis cylinder and cell contents is undisputed.
137. The evidence at present stands thus: There are numerous multipolar
cells which have no traceable connection with nerve-fibres; and fibres
which have no direct connection with multipolar cells. By the first
I do not mean the disputed apolar cells, I mean cells in the gray
substance of the centres which send off processes that subdivide and
terminate as fibrils in the network of the Neuroglia (Figs. 16, 18).
It is indeed generally assumed that these have each one process--the
axis-cylinder process--which is prolonged as a nerve-fibre; nor would
it be prudent to assert that such is never the case; though it would
be difficult to distinguish between a fibre which had united with a
process and a fibre which was a prolongation of a process, in both
cases the neuroplasm being identical. I only urge that the assumption
is grounded not on anatomical evidence, but on a supposed necessary
postulate. All that can be demonstrated is that some processes
terminate in excessively fine fibrils; and occasionally in thousands
of specimens processes have been traced into dark-bordered fibres.
It is true that they often present appearances which have led to
the inference that they did so terminate--appearances so deceptive
that Golgi and Arndt independently record observations of unbranched
processes having the aspect of axis cylinders being prolonged to
a considerable distance (600 μ in one case), yet these were found
to terminate _not_ in a dark-bordered fibre, but in a network of
fibrils.[166]
138. While it is thus doubtful whether dark-bordered fibres are always
immediately connected with cells, it is demonstrable that multitudes
of fibres have only an indirect connection with cells, being developed
as outgrowths from other fibres. Dr. Beale considers that in each
such outgrowths have their origin in small neuroplasmic masses (his
“germinal matter”). That is another question. The fact here to be
insisted on is that we often find groups of cells with only two or
three fibres, and groups of fibres where very few cells exist. Schröder
van der Kolk says that in a sturgeon (_Accipenser sturio_) weighing 120
pounds he found the spinal cord scarcely thicker than that of a frog;
the muscles of this fish are enormous, and its motor nerves abundant;
yet these nerves entered the cord by roots no thicker than a pig’s
bristle; and in the very little gray matter of the cord there was only
a cell here and there found after long search. Are we to suppose that
these rare cells were the origins of all the motor and sensory nerves?
A similar want of correspondence may be noticed elsewhere. Thus in the
spinal cord of the Lamprey my preparations show very few cells in any
of the sections, and numerous sections show none at all. Stieda counted
only eight to ten cells in each horn of some osseous fishes, except
at the places where the spinal roots emerged. In the eel and cod he
found parts of the cord quite free from cells, and in other parts found
two, three, never more than ten. In birds he counted from twenty-five
to thirty. Particular attention is called to this fact of the eel’s
cord being thus deficient, because every one knows the energetic
reflex action of that cord, each separate segment of which responds to
peripheral stimulation.
It may indeed be urged that these few cells were the origin of all
the fibres, the latter having multiplied by the well-known process of
subdivision; and in support of this view the fact may be cited of the
colossal fibres of the electric fishes, each of which divides into
five-and-twenty fibres, and in the electric eel each fibre is said
by Max Schultze to divide into a million of fibrils. But I interpret
this fact otherwise. It seems to me to prove nothing more than that
the neuroplasm has differentiated into few cells and many fibres.
And my opinion is grounded on the evidence of Development, presently
to be adduced. If we find (and this we do find) fibres making their
appearance anywhere _before_ multipolar cells appear, the question is
settled.
139. Dr. Beale regards the large caudate cells of the centres as
different organites from the oval and pyriform cells, and thinks they
are probably stations through which fibres having different origins
merely pass, and change their directions; and Max Schultze says that
no single fibril has been found to have a central origin; every fibril
arises at the periphery, and passes through a cell, which is thus
crossed by different fibrils.[167] (Comp. Fig. 17.)
The teaching of Development is on this point of supreme importance.
Unhappily there has not yet been a sufficient collection of systematic
observations to enable us to speak very confidently as to the
successive stages, but some negative evidence there is. The changes
take place with great rapidity, and the earliest stages have hardly
been observed at all. Although for several successive years I watched
the development of tadpoles, the difficulties were so great, and the
appearances so perplexing, that the only benefit I derived was that of
being able the better to understand the more successful investigations
of others. Four or five days after fecundation is the earliest period
of which I have any recorded observation; at this period the cerebral
substance appeared as a finely granular matter, having numerous lines
of segmentation marking it off into somewhat spherical and oval masses,
interspersed with large granules and fat globules. Here and there
hyaline substance appeared between the segments. Similar observations
have since been recorded by Charles Robin in the earliest stages
of the Triton.[168] He says that when the external gills presented
their first indications, nuclei appeared, each surrounded by a rim of
hyaline substance, from which a pale filament was prolonged at one end,
sometimes one at both ends, and this filament subdivided as it grew
in length until it had all the appearance of an axis cylinder. This,
however, he says, is a striation, not a fibrillation; he refuses to
admit that the axis cylinder is a bundle of fibrils. He further notices
the simultaneous appearance of amorphous substance; and as this is
several days before there is any trace of a _pia mater_, or proper
connective tissue, he urges this among the many considerations which
should prevent the identification of neuroglia with connective tissue.
In a very young embryo of a mole (I could not determine its age) the
cortex of the hemispheres showed granular amorphous substance, in
which were embedded spherical masses of somewhat paler color, which
had no nuclei, and were therefore not cells. Besides these, there were
nucleated masses (apolar cells, therefore) and more developed cells,
unipolar, bipolar, and tripolar. Not a trace of a nerve-fibre was
visible. In agreement with this are the observations of Masius and Van
Lair, who cut out a portion of the spinal cord in a frog, and observed
the regenerated tissue after the lapse of a month. It contained apolar,
bipolar, and multipolar cells, together with “corpuscles without
processes, for the most part larger than the cells, and appearing to be
mere agglomerations of granules,”--these latter I suppose to have been
what I describe as segmentations of the undeveloped substance. Gray
fibres, with a few varicose fibres, also appeared.[169]
140. The admirable investigations of Franz Boll have given these
observations a new significance. He finds in the cerebral substance
of the chick on the third or fourth day of incubation a well-marked
separation between the neuroglia and nerve-tissue proper. Fig. 24, A,
represents three nerve-cells, each with its nucleus and nucleolus,
and each surrounded with its layer of neuroplasm. The other four
masses he regards as nuclei of connective tissue. Three days later the
distinction between the two is more marked (Fig. 24, B). Not only have
the nerve-cells acquired an increase of neuroplasm, they also present
indications of their future processes, which at the twelfth day are
varicose (Fig. 24, C). (All this while the connective corpuscles remain
unchanged.) Although Boll was unable to trace one of these processes
into nerve-fibres, he has little doubt that they do ultimately become
(unite with?) axis cylinders.
[Illustration: Fig. 24.--_Embryonic nerve-cells._]
[Illustration: Fig. 25.--_Embryonic nerve-fibres._]
It is difficult to reconcile such observations with the hypothesis of
the cells being simply points of _reunion of fibrils_. We see here
multipolar cells before any fibrils appear. Respecting the development
of the white substance, i. e. the nerve-fibres, Boll remarks that in
the _corpus callosum_ of the chick the first differentiation resembles
that of the gray substance.
The polygonal and spindle-shaped cells represented in Fig. 25, A, are
respectively starting-points of connective and neural tissues. The
spindle-shaped cells elongate, and rapidly become bipolar. This is
supposed to result in the whole cell becoming transformed into a fibre,
the nucleus and nucleolus vanishing; but the transformation is so rapid
that he confesses that he was unable to trace its stages; all that can
positively be asserted is that one or two days after the appearance
presented in Fig. 25, B, the aspect changes to that of fibrils. The
columns of polygonal cells between which run these fibrils, he regards
as the connective corpuscles described by several anatomists in the
white substance both of brain and cord, and which are sometimes
declared to be multipolar nerve-cells.[170]
141. Dr. Schmidt’s observations on the human embryo were of course
on tissue at a very much later stage. According to him, the fibrils
of the axis cylinders are formed by the linear disposition and
consolidation of elementary granules. The fibrils thus formed are
separated by interfibrillar granules which in time become fibrils. Not
earlier than three months and a half does the formation of individual
axis cylinders begin by the aggregation of these fibrils into minute
bundles, which are subsequently surrounded by a delicate sheath.[171]
142. With respect to the transition of the spindle-shaped cells into
fibrils, since there is a gap in the observations of Boll, and since
those of Schmidt are subsequent to the disappearance of the cells,
and in both cases all trace of nucleus has disappeared, I suggest
that we have here an analogy with what Weismann has recorded of the
metamorphoses of insects. In the very remarkable memoir of that
investigator[172] it is shown that the metamorphoses do not take place
by a gradual modification of the existing organs and tissues, but by a
_resolution_ of these into their elements, and a _reconstruction_ of
their elements into tissues and organs. The muscles, nerves, tracheæ,
and alimentary canal, undergo what may be called a fatty degeneration,
and pass thence into a mere blastema. _It is out of these ruins of the
old tissues that the new tissues are reconstructed._ On the fourth day
the body of the pupa is filled with a fluid mass--a plasma composed of
blood and dissolved tissues. The subsequent development is thus in all
essential respects a repetition of that which originally took place in
the ovum.[173]
Two points are especially noticeable: First, that in this resolved
mass of granules and fat globules there quickly appear large globular
masses which develop a fine membrane, and subsequently nuclei. A glance
at the figure 51 of Weismann’s plates reveals the close resemblance to
the earliest stages of nerve-cells; and the whole process recalls the
regeneration of nerves and nerve-centres after their fatty degeneration.
Secondly, the nerves reappear in their proper places in the new
muscles, and this at a time when the nerve-centres are still unformed;
so that the _whole peripheral system is completely rebuilt in absolute
independence of the central system_. The idea, therefore, that
nerve-fibres are the products of ganglia must be relinquished. This
idea is further discountenanced by Boll’s observations, which show that
the fibre-cells are from the first different from the ganglionic cells;
and by the observations of Foster and Balfour, that “fibres are present
in the white substance on the third day of incubation”; _whereas cell
processes do not appear until the eighth day_. Foster and Balfour are
inclined to believe “that even on the seventh day it is not possible
to trace any connection between the cells and fibres.” In the later
stages, the connection is perhaps established.[174]
143. We may, I think, conclude from all this that in the higher
vertebrates the white substance of brain and cord is not the direct
product of the gray substance; in other words, that here nerve-fibres,
even if subsequently in connection with the ganglionic cells, have
an independent origin. They may grow towards and blend with cell
processes; they are not prolongations of those processes. They may be
identical in structure and property, as one muscle is identical with
another, but one is not the parent of the other.
144. Sigmund Mayer emphatically declares that in no instance has he
traced a cell process developed into a dark-bordered nerve-fibre.
The process, he says, may often be traced for a certain distance
alongside of a fibre; but it then suddenly ceases, whereas the fibre
is seen continuing its course unaltered. Still more conclusive is the
evidence afforded by nerves having only very few fibres (2–4 sometimes
in the frog), which have, nevertheless, a liberal supply of cells,
visible without preparation. Valentin counted twenty-four cells in a
nerve which had but two fibres.[175] Now although it is possible to
explain the presence of numerous fibres with rare cells either as due
to subdivisions of fibres, or to the fibres having cells elsewhere
for their origin, it is not thus that we can explain the presence of
numerous cells which have no fibres developed from their processes.
145. With regard to this observation of the cell process running
alongside of the fibre, the recent researches of Ranvier may throw
some light on it. He describes the cells in the spinal ganglia as all
unipolar; each single process pursues a more or less winding course
as a fibril, often blending with others, till it reaches one of the
fibres from the sensory root. It blends with this fibre at the annular
constriction of the fibre, becoming here incorporated with it, so that
a T-shaped fibre is the result.[176] If this should be confirmed, it
would reconcile many observations; but it would greatly disturb all
current interpretations. Ranvier remarks that it is no longer tenable
to suppose that the ganglionic cell is a centre, sensory or motor,
receiving the excitation or sending forth a motor impulse; for if the
fibril issuing from a cell becomes laterally soldered to a nerve-fibre,
there is no possibility of saying in which direction this cell receives
the excitation, nor in which it transmits the impulse.
146. We have seen good reason to conclude that the essential element of
the nerve--the axis cylinder--is the same substance as the neuroplasm
which forms the essential element of the cell. At any rate, we are
quite certain that the cell process is neuroplasm. On this ground there
is no difficulty in understanding that a cell process may sometimes be
drawn out into an axis cylinder (as indeed we see to be the case in
the invertebrata and electric fishes); while again in numerous other
cases the nerve-fibre has an independent origin, being, in short, a
differentiation from the neuroplasm which has become a fibre instead
of a cell. It is clear from the observations of Rouget on Development,
and of Sigmund Mayer on Regeneration, that fibres, nuclei, and cells
become differentiated from the same neuroplasm, those portions which
are not converted into fibres remaining first as lumps of neuroplasm,
then acquiring a nucleus, and some of these passing into cells. I mean
that between fibres, nuclei, and cells there are only morphological
differences in an identical neuroplasm.[177] If this is in any degree
true, it will not only explain how fresh fibres may be developed in the
course of fibres, branching from them as from trunks, and branchlets
from branchlets, twigs from branchlets, the same conditions of growth
being present throughout; it will also completely modify the notion
of any physiological distinction between cell and fibre greater than
can be assigned to the morphological differences. We shall then no
longer suppose that the cell is the fountain whence the fibre draws its
nutrition and its “force”; and this will be equally the case even if we
admit that a cell is, so to speak, the germ from which a whole plexus
of fibres was evolved, for no one will pretend that the “force” of an
organism is directly derived from the ovum, or that the ovum nourishes
the organism.
147. At this stage of the discussion it is needful to consider a point
which will spontaneously occur to every instructed reader, I mean the
interesting fact discovered by Dr. Waller, that when a sensory root was
divided, the portion which was still in connection with the ganglion
remained unaltered, whereas the portion which was only in connection
with the spinal cord degenerated; and _vice versa_, when a motor root
was divided, the portion connected with the cord remained unaltered,
the portion severed from the cord degenerated. The observation has
been frequently confirmed, and the conclusion drawn has been that the
cells in the ganglion of the posterior root are the nutritive centres
of posterior nerves, the cells in the anterior horn of the cord being
the nutritive centres of the anterior nerves. Another interpretation
is however needed, the more so because the fact is not constant.[178]
True of some nerves, it is not true of others. Vulpian found that
when he cut out a portion of the lingual nerve, and transplanted
it by grafting under the skin of the groin, where of course it was
entirely removed from all ganglionic influence, it degenerated, but it
also regenerated. Pathological observations convinced Meissner that
the ganglia are wholly destitute of an influence on the nutrition of
the vagus; and Schiff proved experimentally that other ganglia were
equally inoperative, since motor nerves could be separated from the
spinal cord without degeneration.[179] Not however to insist on this,
nor on the other facts of regeneration, in the absence of ganglionic
influence, let us remark that Dr. Waller’s examples would not be
conclusive unless the teaching of Embryology could be disproved. That
nerves degenerate when separated from ganglia is a fact; but it is also
a fact that muscles degenerate when separated from a nerve-centre; yet
we do not suppose the nerve-centre to nourish the muscles. And against
the fact that the sensory nerve remains unaltered only in that portion
which is connected with the ganglion, we must oppose the observations
of Kölliker and Schwalbe,[180] who affirm that none of the fibres
which enter the posterior columns of the spinal cord have any direct
connection with the cells of the ganglion on the posterior root. The
cells of this ganglion they declare to be unipolar (in the higher
vertebrates), and the fibres in connection with these cells are not
those which pass to the cord, but all of them pass to the periphery.
According to Ranvier, the fibres from the cells join the fibres of
the posterior root. Schwalbe found that if the spinal nerve be firmly
grasped and _steadily_ drawn, it will often be pulled from its sheath,
and the ganglion laid bare;[181] in this ganglion all the cells are
found undisturbed, which could not be the case had fibres from _those_
cells entered the cord, since the traction would necessarily have
disturbed them.
RECAPITULATION.
148. At the opening of this chapter mention was made of the besetting
sin of the analytical tendency, namely, to disregard the elements
which provisionally had been set aside, and not restore them in the
reconstruction of a synthetical explanation. Familiar experiences
tell us that a stimulus applied to the skin is followed by a muscular
movement, or a glandular secretion; sometimes this takes place without
any conscious sensation; sometimes we are distinctly conscious of
the stimulus; and sometimes we consciously will the movement. These
facts the physiologist tries to unravel, and to trace the complicated
processes involved. The neurologist of course confines himself
exclusively to the neural processes; all the other processes are
provisionally left out of account. But not only so: the analytical
tendency is carried further, and even in the neural process the
_organs_ are neglected for the sake of the nervous _tissue_, and the
nervous tissue for the sake of the _nerve-cell_. The consequence has
been that we have an explanation offered us which runs thus:--
149. The nerve-cell is the supreme element, the origin of the
nerve-fibre, and the fountain of nerve-force. The cells are connected
one with another by means of fibres, and with muscles, glands, and
centres also by means of fibres, which are merely channels for the
nerve-force. A stimulus at the surface is carried by a sensory fibre
to a cell in the centre; from that point it is carried by another
fibre to another cell; and from that by a third fibre to a muscle:
a reflex contraction results. This is the elementary “nervous arc.”
But this arc has also higher arcs with which it is in connection: the
sensory cell besides sending a fibre directly to a motor cell, also
sends one upwards to the cerebral centres; and here again there is a
nervous arc, so that the cerebral centre sends down an impulse on the
motor cells, and the contraction which results is due to a volitional
impulse. The transmission of the stimulation which in the first case
was purely physical, becomes in the latter case psychical. The sensory
impression is in one cell transformed into a _sensation_, in another
cell into an _idea_, in a third cell into a _volition_.
150. This course is described with a precision and a confidence which
induces the inexperienced reader to suppose that it is the transcript
of actual observation. I venture to say that it is imaginary from
beginning to end. I do not affirm that no such course is pursued,
I only say no such course was ever demonstrated, but that at every
stage the requisite facts of observation are either incomplete or
contradictory. First, be it noted that the actions to be explained are
never the actions of organs so simple as the description sets forth.
It is not by single fibres and cells that the stimulus is effected,
but by complex nerves and complex centres. Only by a diagrammatic
artifice can the fibre represent the nerve, and the cell the centre.
In reality the cells of the centre (supposing them to be the _only_
agents) act in groups, and Anatomy should therefore show them to be
mutually united in groups--which is what no Anatomy has succeeded in
showing, unless the Neuroglia be called upon. Secondly, be it noted
that the current scheme of the relations between cells and fibres is
one founded on physiological postulates, not on observation. Thirdly,
much of what is actually observed is very doubtful, because we do not
know whether the appearances are normal, or due to modes of preparation
and post-mortem changes. We cannot at present say, for instance,
whether the fibrillated appearance of cell contents and axis cylinder
represents the living structure or not. We may either suppose that
the neuroplasmic pulp splits longitudinally into fibres, or that
neuroplasmic threads resolve themselves into a homogeneous pulp--the
axis cylinder may be a condensation of many fibrils, or the fibrils may
be a resolution of the substance.
151. Let us contrast step by step the Imaginary Anatomy found in the
text-books with the Objective Anatomy as at present disclosed by the
researches of all the chief workers. Imaginary Anatomy assumes that the
sensory fibre passes from a surface into the cells of the posterior
horn of the spinal cord. Objective Anatomy sees the fibre pass into the
gray substance, but declares that no direct entrance of a fibre into a
cell is there visible.
Imaginary Anatomy assumes that from the sensory cells of the gray
substance pass fibres in connection with the motor cells of the
anterior horn, thus forming a direct channel through which the
excitation of a sensory cell is transmitted to a motor cell. Objective
Anatomy fails to discover any such direct channel--no such fibres are
demonstrable.
Imaginary Anatomy assumes that from the motor cells issue fibres which
descend to the muscles and glands, and carry there the motor impulses
and the “mandates of the will.” Objective Anatomy fails to find at
the utmost more than a probability that these cells are continued
as fibres, a probability which is founded on the rare facts of cell
processes having been seen extending into the roots of the nerves, and
of a cell process having occasionally been seen elsewhere continuous
with a dark-bordered fibre. Granting, however, that this probability
represents the fact, we have thus only one part of the “nervous arc”
which can be said to have been verified.
Imaginary Anatomy further assumes that this nervous arc is connected
with cerebral centres by means of fibres going upwards from the
posterior cells, and fibres descending downwards to the anterior
cells. Objective Anatomy sees nothing of the kind. It sees fibres
entering the gray substance, and there lost to view in a mass of
granular substance, fibrils, neuroblasts, and cells. There _may
be_ uninterrupted fibres passing upwards and downwards; but it
is impossible to see them. And if we are told that physiological
interpretations demand such a structure, we may fairly ask if this, and
this only, is the structure which is adequate to the propagation of
excitation? Now it seems to me that another kind of structure, and one
more closely agreeing with what is observed, better answers the demands
of Physiology. This will be more evident after the Laws of Nervous
Action have been expounded in the succeeding chapter. Meanwhile we may
remark that the arrangement of cells and fibres which is imagined as
the mechanism of propagation and reflexion is absolutely irreconcilable
with the teaching of Experiment: for the spinal cord may be cut through
anywhere, without destruction of the transmission of sensory and motor
excitations, provided only a small portion of gray substance be left to
establish the continuity of the axis. Divide all the substance of the
posterior half in one place, and all the substance of the anterior half
in another, yet so long as there is a portion of gray substance left
as a bridge between the lower and upper segments, the transmission of
sensory and motor excitations will take place.
152. In other essential respects we have to note that the anatomical
evidence for the current interpretations is absolutely deficient or
contradictory. There is no adequate warrant for the assumption that all
nerves have their origin in ganglia, all fibres in cells. Such evidence
as at present exists is against that supposition, and in favor of the
supposition that both cell and fibre are differentiations of a common
neuroplasm, sometimes directly, sometimes indirectly continuous.
Fibres, and plexuses of fibres, interspersed with cells irregularly
distributed--now singly, now in small groups, now in larger and larger
groups--constitute the _figured_ elements of nerve-tissue; and even if
we set aside the _amorphous_ substance as indifferent or subordinate,
we have still no ground for assigning the supremacy, much less the sole
significance, to the cells. The grounds of this denial have been amply
furnished in our exposition. For, let it be granted that nerve-cells
are the origins of the fibres and the sources of their nutrition--a
point which is eminently disputable--this would in no sense help the
physiological hypothesis of the cell as the fountain of Neurility. If
the fibre is simply the cell-contents drawn out longitudinally, if
its essential element is identical with the essential element of the
cell, then we can no more ascribe to the cell the exclusive property
of Neurility than we can draw a lump of lead out into a wire, and then
ascribe different properties to the thin end and the thick end. But
on this point it is needless to speculate, since we have experimental
evidence proving that the nerve-fibre has its Neurility even when
separated from the cell, or even from the ganglion.
153. It is possible--I do not see sufficient evidence for a stronger
assertion--that the cells are the nutritive sources of the fibres. They
may represent the alimental rather than the instrumental activities of
nervous life. (Compare PROBLEM I. § 42.) My contention is that in any
case they are not the supreme elements of the active tissue, and in no
sense can they be considered as _organs_. Only confusion of ideas could
for a moment permit such language, or could assign central functions
to cells which are elements of tissue. If the cell be credited with
such powers anywhere, it must be credited with them everywhere. Now I
ask what conceivable central function can be ascribed to a cell which
terminates the fibre in a peripheral ganglion, or which is merely
an enlargement in the course of a fibre in a nerve-bundle? Besides
the facts already adduced, let attention be called to this: If a
nerve-bundle from the _submucosa_ of the intestine be examined, there
appear among the fibres many nuclei (neuroblasts), and occasionally
cells, unipolar and bipolar. These cells--if we may trust the
observations of Rouget on the earliest development of nerves, and of
Sigmund Mayer on regenerated nerves--are simply more advanced stages of
evolution of the neuroblasts; but whatever their genesis may be, there
can be nothing in the nature of a central function assigned to them.
154. It may be asked, What part can we assign to cells in neural
actions if they are apolar, unipolar, and even when multipolar,
isolated from each other, and from fibres? I confess that I have
no answer ready, not even an hypothesis. Until some rational
interpretation of the cell be given we must be content to hold an
answer in suspense. What I would urge is that we are precipitate
in assuming that the anatomical connection between one element and
another must necessarily be that of a fibre. In a semi-fluid substance,
such as neurine, continuity may be perfect without solid fibres: the
amorphous substance and the plasmode may as well transmit waves of
molecular motion from one part of the tissue to another, and therefore
from cell to cell, or from cell to fibre, as a figured substance
may. When the posterior root enters the gray substance of the cord,
there is no more necessity for its fibres passing directly into the
cells of that gray substance, in order to excite their activity, than
there is for a wire to pass from the bell to the ear of the servant,
who hears the vibrations of the bell through the pulsations of the
intervening air upon her tympanum. Look at the structure of the retina,
or the cerebellum, and you will find that the ganglionic cells which
have processes passing in a direction contrary to that whence the
stimulus arrives, have none where continuity of fibre and cell would
be indispensable on the current hypothesis. Light stimulates the
rods and cones, but there are no nerve-fibres, hitherto discovered,
passing from these to the ganglionic cells; instead of that there is
a ground-substance thickly interspersed with granules and nuclei.
_From_ the cells we see processes issue; _to_ the cells none are seen
arriving. So with the cerebellum. The large cells send their processes
upwards to the surface; but downwards towards the white substance the
processes are lost in the granular layer, which most histologists
regard as connective tissue.
155. A mere glance at nervous tissue in any part will show that cells
are far from forming the principal constituents. In the epidermis or
a gland the cell is obviously the chief element, forming the bulk of
the tissue, and being the characteristic agent. In nerve-tissue, as in
connective tissue, the reverse is the case. We must therefore cease to
regard the cell as having the importance now attached to it, and must
rather throw the emphasis on the fibres and neuroglia.
156. Before quitting this subject let a word be said on the amazing
classification which has attained wide acceptance (although rejected by
the most eminent authorities), founded on the size of the cells--the
large multipolar cells being specified as motor, the smaller cells as
sensory, while those of an intermediate size are sympathetic. I forbear
to dwell on the development of this notion which specifies sensational,
ideational, and emotional cells, because this does not pretend to have
a basis in observation; whereas there are anatomical facts which give
a certain superficial plausibility to the original classification.
The conception is profoundly unphysiological; yet, if the anatomical
evidence were constant, one might give it another interpretation. The
evidence is, however, not constant. Large cells are found in regions
assigned to sensory nerves, and small cells in motor regions. In the
spinal cord of the tortoise Stieda declares that the so-called motor
cells are limited to the cervical and lumbar enlargements; all the rest
of the motor region being absolutely destitute of them.[182] Again
look at the cells of the retina--no one will assign motor functions to
them--yet they are the same as those of the cerebellum and the anterior
horns of the spinal cord. (It is worth a passing mention that the
structure of the nervous parts of the retina more closely resembles
that of the cerebellum than of the cerebrum.)
157. While our knowledge of the cell is thus far indeed from having
the precision which the text-books display, and in no sense warrants
the current physiological interpretations, our knowledge of fibres and
neuroglia is also too incomplete for theoretic purposes. We know that
the axis cylinder is the essential element; but we are still at a loss
what part is to be assigned to the medullary sheath. There is indeed a
popular hypothesis which pronounces it to be the means of _insulating_
the fibre, and thus preserving the isolated conduction of nerve-force.
Being of a fatty nature, this insulating office was readily suggested
in agreement with the assumption that Neurility was Electricity. Now,
without discussing whether Neurility is or is not Electricity, even
admitting the former to be satisfactorily proved, I must remark that
the admission still leaves the medullary sheath incapable of fulfilling
the supposed office, since not only is there no such sheath in most of
the invertebrates and in the sympathetic nerves of vertebrates, but
even in those nerves which have the sheath it is precisely in places
where the insulation would be most needed--namely, just before the
terminations of the fibres in muscles and in centres--that the sheath
is _absent_. This is as if we tried to conduct water through a pipe
which fell short at both ends--before it left the cistern, and before
it reached the spot to be watered. If there is a tendency in Neurility
to spread wherever it is not insulated by a medullary sheath, then
before reaching the centres and the muscles, it must, on the insulating
hypothesis, dribble away!
158. The facts expressed in the “law of isolated conduction” are
important, and are difficult of explanation; but it is obvious that
they cannot be referred to the presence of the medullary sheath. Nor
indeed will any insight into the propagation of stimulation through
the central axis be intelligible until we have reformed our anatomical
theories, and taken the Neuroglia into account. The theory which
connects every fibre directly with a cell, and every cell with another
by anastomosis--even were it demonstrated--would not explain the law
of isolated conduction. Butzke cogently remarks[183] that such a
disposition of the elements should render all neural paths invariable;
whereas the fact is that they are very variable. We learn to perform
actions, and then we unlearn them; the paths are traversed now in
one direction, now in another. Fluctuation is the characteristic
of central combinations. And for this fluctuating combination of
elements a corresponding diversity is required in the possible
channels. This seems to be furnished by the network of the Neuroglia.
See the representation copied from Butzke’s plate, and note how the
cell-process blends with the meshes of the Neuroglia. Is it fanciful
to regard this network of fibrils as having somewhat the relation of
capillaries to blood-vessels? Did we not experimentally know that the
capillaries are terminal blood-vessels, we should not suspect it from
mere examination of the structure.
159. Having insisted that our knowledge is insufficient for any
explanation of the “law of isolated conduction,” I can only suggest a
path of research which may lead to some result. What we know is that
some stimulations are propagated from one end of the cerebro-spinal
axis to the other in definitely _restricted_ paths, while others are
_irradiated_ along many paths. In the succeeding chapter this will be
more fully considered; what we have here to note is that the manifold
irradiations of a stimulation have an anatomical substratum in the
manifold sub-divisions of the network of fibrils and the amorphous
substance in which they penetrate.
[Illustration: Fig. 26.--_Nerve-cells with processes terminating in
neuroglia._]
160. In conclusion, I would say, let no one place a too great
confidence in the reigning doctrines respecting the elementary
structure of the nervous system, but accept every statement as a
“working hypothesis” which has its value in so far as it links together
verified facts, or suggests new research, but is wholly without value
in so far as it is made a basis of deductions not otherwise verified.
Hypotheses are indispensable to research, but they must be accompanied
by vigilant scepticism. Imagination is only an enemy to Science when
Scepticism is asleep.
CHAPTER VIII.
THE LAWS OF NERVOUS ACTIVITY.
161. The foregoing remarks have had the object of showing how little
substantial aid Psychology can at present derive from what is known
of the elementary structure of the nervous system, indispensable
as an accurate knowledge of that structure must be to a complete
analysis of its functions. This caution has been specially addressed
to those medical and psychological students whose researches leave
them insufficient leisure to pursue microscopical investigations
for themselves, and who are therefore forced to rely on second-hand
knowledge, which is usually defective in the many qualifying
considerations which keep scepticism vigilant. Relying on positive
statements, and delusive diagrams which only display what the observer
_imagines_, not what he actually _sees_, they construct on such data
theories of disease, or of mental processes; or else they translate
observed facts into the terms of this imaginary anatomy, and offer the
translation as a new contribution to Science.
162. But little aid as can at present be derived from the teaching of
the microscope, some aid Psychology may even now derive from it. The
teaching will often serve, for instance, to correct the precipitate
conclusions of subjective analysis, which present artificial
distinctions as real distinctions, separating what Nature has united.
It will show certain organic connections not previously suspected;
and since whatever is organically connected cannot functionally be
separated, such sharply marked analytical distinctions as those of
periphery and centre, or of sensation and motion, must be only regarded
as artificial aids. The demonstration of the indissoluble union of
the tissues is a demonstration of their functional co-operation. So
also the anatomical demonstration of the similarity and continuity of
all parts of the central system sets aside the analytical separation
of one centre from another, except as a convenient artifice; proving
that cerebral substance is one with spinal substance, having the same
properties, the same laws of action.
For the present, Psychology must seek objective aid from Physiology
and Pathology rather than from elementary Anatomy. In the paragraphs
which are to follow I shall endeavor to select the chief laws of
nervous activity which the researches of physiologists and pathologists
disclose. By these laws we may direct and control psychological
research.
THE ENERGY OF NEURILITY.
163. Vitality is characterized by incessant molecular movement, both
of composition and decomposition, in the building up of structure and
the liberation of energy. The life of every organism is a complex of
changes, each of which directly or indirectly affects the statical
and dynamical relations, each being the resultant of many co-operant
forces. In the nourishment of every organite there is an accumulation
of molecular _tension_, that is to say, stored-up energy in a latent
state, ready to be expended in the activity of that organite; and this
expenditure may take place in a steady flow, or in a sudden gush.
The molecular movements under one aspect may be called convergent,
or _formative_: they build the structure, and tend to the state of
equilibrium which we call the statical condition of the organite,
i. e. the condition in which it is not active, but ready to act.
Perfect equilibrium is of course never attained, owing to the
incessant molecular change: indeed Life is inconsistent with complete
repose. Under another aspect the molecular movements may be called
_discharging_: they constitute the dynamic condition of the organite,
in which its functional activity appears. The energy is now diverted,
liberated, and the surplus, over and above that which is absorbed in
formation, instead of slowly dribbling off, gushes forth in a directed
stream. The slow formation of a secretion in a gland-cell, and the
discharge of that secretion, will illustrate this; or (if muscular
_tone_ be admitted) the incipient contraction of the chronic state, and
the complete contraction of the dynamic state, may also be cited.
164. The discharge which follows excitation may thus be viewed as
a _directed quantity_ of molecular movement. Because it is always
strictly relative to the energy of tension, and is inevitable when
that tension attains a certain surplus over what is required in
construction, there is a limit, 1°, to the growth and evolution of
every organite, and every organism (comp. Problem I. § 118), and, 2°,
to its dynamical effect. When there is no surplus, the organite is
incapable of discharge: it is then exhausted, i. e. will not respond to
stimulus.
165. The speciality of nerve-tissue is its pre-eminence in directive
energy. Like all other tissues, it grows, develops, and dies; but
above all others it has what we call _excitability_, or readiness in
discharging its energy in a directed stream. By its topographical
distribution it plays the functional part of exciting the activity of
other tissues: it transmits molecular disturbance from periphery to
centre, from centre to centre, and from centre to muscles, vessels, and
glands. When a muscle is excited it moves, and when a gland is excited
it secretes; but these actions end, so to speak, with themselves; the
muscle does not directly move any other muscle;[184] the gland does not
directly excite any other gland. The nerve, on the contrary, has always
a wide-spreading effect; it excites a centre which is continuous with
other centres; and in exciting one muscle, usually excites a group.
Hence the nervous system is that _which binds the different organs
into a dynamic unity_. And Comparative Anatomy teaches that there is a
parallelism between the development of this system and the efficient
complexity of the organism. As the tissues become more and more
specialized, and the organs more and more individualized, they would
become more and more unsuited to the general service of the organism,
were it not that a corresponding development of the nervous system
brought a unifying mechanism.
The great instability of neurine, in other words, its high degree of
tension, renders it especially apt to disturb the tension of other
tissues. It is very variable; and this variability will have to be
taken into account in explaining the restriction of discharges to
particular centres. A good example of exaggerated tension is furnished
by strychnine poisoning. The centres are then so readily excitable
that a touch, or a puff of cold air on the skin, will determine
convulsions. And it is worthy of remark that for some hours after this
convulsive discharge the centres return to something like their normal
state; and the animal may then be stroked, pinched, or blown upon
without abnormal reactions. But during this interval the centres are
slowly accumulating excess of tension from the poisoned blood; and at
the close, convulsions will again follow the slightest stimulus. This
alternation of exhaustion and recrudescence is noticed by Schröder
van der Kolk in the periodicity of the phenomena exhibited in spinal
disease.[185]
THE PROPAGATION OF EXCITATION.
166. Understanding, then, that the propagation of an excitation
depends on the state of tension of the tissue, and always follows
the line of least resistance, whichever that may be at the moment,
we have to inquire whether the transmission takes place only in one
direction, from periphery to centre in sensory nerves, and from centre
to periphery in motor nerves? By most physiologists this is answered
affirmatively. Indeed a special property has been assigned to each
nerve, in virtue of this imaginary limitation of centripetal and
centrifugal conduction. The “nerve-current” (accepted as a physical
fact, and not simply a metaphor) is supposed to “flow” from the
central cells along the motor nerve to the muscles; but by a strange
oversight the current is also made to “flow” _towards_ the central
cells which are said to produce it! Now although the fact may be, and
probably is, that normally the sensory nerve, being stimulated at its
peripheral end, propagates the stimulation towards the centre, and the
motor nerve propagates its central stimulation towards the periphery,
the question whether each nerve is not capable of transmission in
both directions is not thus answered. _A priori_ it is irrational to
assert that nerves fundamentally alike in composition and structure
are unlike in properties; and we might as well suppose that a train
of gunpowder could only be fired at one end, as to suppose that a
nerve could only be excited at one end. And how does the evidence
support this _a priori_ conclusion? Dubois Reymond proved that each
nerve conducted electricity in both directions; but as Neurility
has not been satisfactorily shown to be identical with the electric
current, this may not be considered decisive. Such a doubt does not
hang over the following facts. M. Paul Bert, pursuing John Hunter’s
curious experiments on animal _grafting_, has grafted the tail of
a rat under the skin of the rat’s back, the tip of the tail being
inserted under the skin, its base rising into the air, so that there
is here an inversion of the normal position. In the course of time
Sensibility gradually reappears in this grafted tail; and at the
end of about twelve months the rat not only feels when the tail is
pinched, but knows _where_ the irritation lies, and turns round to bite
the pincers.[186] Here we have a case of a sensory nerve reversed,
yet transmitting stimulation from the base to the tip of the tail,
instead of from the tip to the base, as in a normal organ. Vulpian
and Philippeaux having divided two nerves, united the central end of
the sensory nerve with the peripheral end of the motor nerve; when
the organic union was complete, and each nerve was formed out of the
halves of two different nerves, the effect of pinching one of these
was to produce simultaneously pain and movement, showing that the
excitation was transmitted upwards to the centre, and downwards to the
muscles.[187] It may be compared with a train of gunpowder having a
loaded cannon at one end and a bundle of straw at the other, when if a
spark be dropped anywhere on this train, the flame runs along in both
directions, explodes the cannon, and sets alight the straw.
167. Indeed we have only to remember the semi-liquid nature of the
axis cylinder to see at once that it must conduct a wave of motion as
readily in one direction as in another. A liquid transmits waves in any
direction according to the initial impulse. There is consequently no
reason for asserting that because the usual direction is centripetal
in a sensory nerve, and centrifugal in a motor nerve, each nerve is
_incapable_ of transmitting excitations in both directions. And I think
many phenomena are more intelligible on the assumption that neural
transmission is in both directions. If the eye is fixed steadfastly
on a particular color during some minutes, the retina becomes
exhausted, and no longer responds to the stimulus of that color: here
the stimulation is of course centripetal. But if instead of looking
intently on the color, the mind (in complete absence of light) pictures
it intently, _this cerebral image is equally capable of exhausting the
retina_; and unless we believe that color is a cerebral, not a retinal
phenomenon (which is my private opinion), we must accept this as proof
of a centrifugal excitation of a sensory tract. Another illustration
may be drawn from the muscular sense. There may be a few sensory fibres
distributed to muscles; but even if the observations of Sachs[188]
should be confirmed, I do not think that all muscle sensations can be
assigned to these fibres, but that the so-called motor fibres must
also co-operate. When a nerve acts upon a muscle, the muscle reacts
on the nerve; and when a nerve acts on a centre, the centre reacts on
the nerve. The agitation of the central tissue cannot leave the nerve
which blends with it unaffected; the agitation of the muscular tissue
must also by a reversal of the “current” affect its nerve. Laplace
points out how the movement of the hand which holds a suspended chain
is propagated along the chain to its terminus, and if when the chain
is at rest we once more set that terminus in motion, the vibration
will remount to the hand.[189] The contraction of a muscle will not
only stimulate the sensory fibres distributed through it, but also, I
conceive, stimulate the very motor fibres which caused the contraction,
since these fibres blend with the muscle.[190]
168. To understand this, it is necessary to remember that the
stimulation of a nerve does not arise[191] in the _changed state_ of
that nerve, but in the _process of change_, i. e. the disturbance of
the tension. The duration of the stimulation is that of the changing
process, and the intensity increases with the differential of the
velocity of change. So that when a nerve which has been excited by a
change of state returns to its former state, this return--being another
change--is a new excitation. That it is not the changed state, but the
change, which is operative, explains the fact noted by Brown Séquard:
a frog poisoned by strychnine, when decapitated and all respiration
destroyed, will remain motionless for days together, if carefully
protected from all external excitation; but its nervous system is in
such a state of tension all this time that the first touch produces
general convulsions. Freusberg also notes that if a brainless frog be
suspended by the lower jaw, and one foot be pinched, the other leg is
moved at first, then quickly droops again, and remains at rest until
the pincers are removed from the pinched foot, when suddenly all four
legs are violently moved by the _stimulation which the simple removal
produces_. Let us also add the well-known and significant fact that
if a nerve be divided rapidly by a sharp razor, neither sensation
nor motion is produced, because the intensity of a stimulus being,
to speak mathematically, _the function of the changing process_, the
duration of the process is in this case too brief. On the same ground
the application of a stimulus will excite no movement, if the force be
very slowly increased from zero to an intensity which will destroy the
nerve; but at any stage a _sudden_ increase will excite a movement.
169. We may group all the foregoing considerations in this formula:
LAW I. Every neural process is due to a sudden disturbance of the
molecular tension. The liberated energy is discharged along the
lines of least resistance.
The conditions which determine the lines of least resistance are
manifold and variable. The nervous system is a continuous whole, each
part of which is connected with diverse organs; but in spite of this
anatomical diversity, the deeper uniformity causes the activity of
each part to depend on and involve the activity of every other, more
or less. By “more or less” is meant, that although the excitation of
one part necessarily affects the state of all the others, because of
their structural community, so that _each sensation and each motion
really represents a change in the whole organism_, yet the responsive
discharge determined in each organ by this change, depends on the
tension of the organ and its centre at that moment. A bad harvest
really affects the whole nation; but its effect is conspicuous on the
welfare of the poor rather than of the rich, although the price of
bread is the same to rich and poor. Nervous centres, and muscular or
glandular organs, differ in their excitability; one condition of this
greater excitability being the greater frequency with which they are
called into activity. The medulla oblongata is normally more excitable
than the medulla spinalis; the heart more than the limbs. Hence a
stimulus which will increase the respiration and the pulse may have no
_appreciable_ effect on the limbs; but some effect it must have.
170. Imagine all the nerve-centres to be a connected group of bells
varying in size. Every agitation of the connecting wire will more or
less agitate all the bells; but since some are heavier than others,
and some of the cranks less movable, there will be many vibrations
of the wire which will cause some bells to sound, others simply to
oscillate without sounding, and others not sensibly to oscillate.
Even some of the lighter bells will not ring if any external pressure
arrests them; or if they are already ringing, the added impulses, not
being rhythmically timed, will _arrest_ the ringing. So the stimulus
of a sensory nerve agitates its centre, and through it the whole
system; usually the stimulation is mainly reflected on the group of
muscles innervated from that centre, because this is the readiest path
of discharge; but it sometimes does not mainly discharge along this
path, the line of least resistance lying in another direction; and the
discharge never takes this path without also irradiating upwards and
downwards through the central tissue. Thus irradiated, it falls into
the general stream of neural processes; and according to the state in
which the various centres are at the moment it modifies their activity.
A nervous shock--physical or mental--sensibly affects all the organs. A
severe wound paralyzes, for a time, parts far removed from the wounded
spot. A blow on the stomach will arrest the heart; a fright will do
the same. Terror relaxes the limbs, or sets them trembling; so does
a concussion: if a frog be thrown violently on the ground, all its
muscles are convulsed; but if the nerves of one limb be divided before
the shock, the muscles of that limb will not be convulsed.
171. We are apt to regard the discharge on the moving organs as if
that were the sole response of a stimulation; but although the most
conspicuous, it is by no means the most important effect. Besides
exciting the muscles, more or less, every neural process has its
influence on the organic processes of secretion, and effects thermal
and electrical changes. Schiff has demonstrated that every sensation
raises the temperature of the brain; Nothnagel, that irritation of a
sensory nerve causes constriction of the cerebral arteries, and hence
cerebral anæmia. Brown Séquard and Lombard find the temperature of
a limb raised when its skin is pinched, and lowered when the skin
_elsewhere_ is pinched. Georges Pouchet has shown that fishes change
color according to the brightness or darkness of the ground over which
they remain; and these changes are dependent on nervous stimulation,
mainly through the eye, division of the optic nerves preventing the
change. These are so many _a posteriori_ confirmations of what _a
priori_ may be foreseen. They are cited here merely to enforce the
consideration, seldom adequately kept before the mind, that every
neural process is a change which causes other changes in the whole
organism.
STIMULI.
172. Stimuli are classed as external and internal, or physical and
physiological. The one class comprises all the agencies in the
External Medium which _appreciably_ affect the organism; the other
class all the changes _in_ the organism which appreciably disturb the
equilibrium of any organ. Although the pressure of the atmosphere, for
example, unquestionably affects the organism, and determines organic
processes, it is not reckoned as a stimulus unless the effect become
appreciable under sudden variations of the pressure. In like manner
the blood is not reckoned among the internal stimuli, except when
sudden variations in its composition, or its circulation, determine
appreciable changes. Because the external stimuli, and the so-called
Senses which respond to them, are more conspicuous than the internal
stimuli and the Systemic Senses, they have unfortunately usurped too
much attention. The massive influence of the Systemic Sensations in
determining the desires, volitions, and conceptions of mankind has not
been adequately recognized. Yet every one knows the effect of impure
air, or a congested liver, in swaying the mental mood; and how a
heavy meal interferes with muscular and mental exertion.[192] What is
conspicuous in such marked effects, is less conspicuously, but not less
necessarily, present in slighter stimuli.
173. A constant pressure on the tympanum excites no sound; only a
rhythmic alternation of pressures will excite the sensation. A constant
temperature is not felt; only changes in temperature. If Light and
Sound were as uniform as the circulation of the blood, or the pressure
of the atmosphere, we should be seldom conscious of the existence of
these stimuli. But because the changes are varied and marked, our
attention is necessarily arrested by them. The changes going on within
the tissues are too graduated to fix the attention; it is only by
considering their cumulative effects that we become impressed with
their importance. For example, the development of the sexual glands
determines conspicuous physical and moral results--we note consequent
effects on voice, hair, horns, structure of the skull and size of the
muscles, no less than the rise of new feelings, desires, instincts,
ideas. Any organic interference with the activity of the ovaries will
alter the moral disposition of the animal: suppression of this organic
process means non-development of the feelings of maternity; the moral
superstructure is absent because its physical basis is wanting.
174. Blood supplies the tissues with their plasmodes; a constant
supply of oxygenated blood is therefore necessary to the vitality of
the tissues. But it is an error to suppose that oxygen is the special
stimulus of nerve-centres, or that their activity depends on their
oxidation; on the contrary, the deficiency of oxygen or surplus of
carbonic acid is that which stimulates. When saturated with oxygen,
the blood paralyzes respiration; when some of the oxygen is withdrawn,
respiration revives. Here--as in all other cases--we have to remember
that differences in degree readily pass into differences in kind,
so that an excess of a stimulus produces a reversal of the effect;
thus although surplus of carbonic acid excites respiratory movements,
excess of carbonic acid causes Asphyxia. Abundance of blood is
requisite for the continuous activity of nerve-centres; but while a
temporary deficiency of blood renders them more excitable, too great a
deficiency paralyzes them. Anæmia, which causes great excitability, and
convulsions (so that nerves when dying are most irritable), may easily
become the cause of the death of the tissue. There are substances which
can only be dissolved by a given quantity of liquid; if this quantity
be in excess, they are precipitated from the solution. There are
vibrations of a given order which cause each string to respond; change
the special order, and the string returns to its repose.
In the stillness and darkness of the night we are excluded from most
of the external stimuli, yet a massive stream of systemic sensations
keeps the sensitive mechanism active, and in sleep directs the dreams.
The cramps and epileptiform attacks which occur during sleep are most
probably due to the over-excitability produced by surplus carbonic
acid. To temporary anæmia may be assigned the strange exaggeration of
our sensations during the moments which precede awakening; and the
greater vividness of dream-images.
It is only needful to mention in passing the varied stimuli by which
cerebral changes act upon the organism. The mention of a name will
cause a blush, a brightening of the eye, a quickening of the pulse. The
thought of her absent infant will cause a flow of milk in the mother’s
breast.
175. We may formulate the foregoing considerations in another law:
LAW II. The neural excitation, which is itself a change, directly
causes a change in the organ innervated, and indirectly in the
whole organism.
The significance of this law is, that although for the convenience
of research and exposition we isolate one organ from the rest of the
organism, and one process from all the co-operant processes, we have to
remember that this is an artifice, and that in reality there is no such
separation.
STIMULATION.
176. Passing now from these general considerations to their special
application, we may formulate the law of stimulation:
LAW III. A faint or moderate stimulation increases the activity
of the organ; but beyond a certain limit, increase of
stimulation diminishes, and finally arrests, the activity.
Duration of stimulation is equivalent to increase.
A muscle stimulated contracts; if the stimulation be repeated,
the muscle becomes tetanized, and in this state has reached its
limit; a fresh stimulation then _relaxes_ the muscle. A very faint
stimulation of the vagus quickens the pulsation of the heart, but a
slight increase, or duration of the stimulation, slackens and arrests
the heart.[193] Every one knows how a moderate feeling of surprise,
pleasure, or pain quickens the heart and the respiration; and how a
shock of surprise, joy, grief, or great physical pain depresses,
and even arrests them. Excess of light is blinding; excess of sound
deafening.
177. The nervous system is incessantly stimulated, and variably.
Hence a great variation in the excitability of different parts. While
the regular and moderate activity of one part is accompanied by a
regular flow of blood to it, so that there is a tolerably constant
rhythm of nutrition and discharge, any irregular or excessive activity
exhausts it, until there has been a nutritive restoration. We can
thus understand how one centre may be temporarily exhausted while
a neighboring centre is vigorous. Cayrade decapitated a frog, and
suspended light weights to each of its hind legs; when either leg was
stimulated, the weight attached to it was raised. After each repetition
the weight was raised less and less, until finally the weight ceased to
be raised: the centre had been exhausted. But now when the other leg,
which had been in repose, was stimulated, it energetically contracted,
and raised its attached weight; showing that its centre was not
exhausted by the action of the other.[194]
178. This seems in contradiction with the principle that the excitation
of one centre is an excitation of all. It also seems in contradiction
with the principle urged by Herzen, that irritation of one sciatic
nerve _diminishes_ the excitability of the opposite leg; and this again
seems contradicted by the principle urged by Setschenow, that although
moderate excitation of one sciatic nerve will diminish the excitability
of the other, a powerful excitation will increase it.
179. All three principles are, I believe, exact expressions of
experimental evidence; and their seeming contradictions may be
reconciled on a wider survey of the laws of neural activity,
interpreted according to the special conditions of each case. These
laws may be conveniently classified as laws of Discharge, and Laws of
Arrest; the second being only a particular aspect of the first.
THE LAW OF DISCHARGE.
180. The physiological independence of organs, together with their
intimate dependence in the organism, and the fact that this organism is
incessantly stimulated from many sides at once, assure us _a priori_
that the “waves” of molecular movement due to each stimulus must
sometimes interfere and sometimes blend with others, thus diverting or
neutralizing the final discharge in the one case, and in the other case
swelling the current and increasing the energy of the discharge. We
are accustomed to speak of one part “playing on another,” sympathizing
with another, and so on; but what is the process expressed in these
metaphors? When an idea, or a painful sensation, quickens the pulse,
or increases the flow of a secretion, we are not to imagine that from
a spot in the cerebrum, or the surface, there is a nerve-fibre going
directly to the heart, or the gland, transmitting an impulse; in each
case the central tissue has been agitated by a sudden change at the
stimulated point, and the discharge on heart and gland is the resultant
of this agitation along the lines of least resistance. The nerves of
the great toe, for example, pass into the spinal cord at a considerable
distance from the spot where the nerves of the arm enter it; when,
therefore, the great toe is pinched, the arm does not move by direct
stimulation of its nerves, but by the indirect stimulation which has
traversed the whole central substance.
181. This is intelligible when we know that the whole central substance
is continuous throughout; but the difficulty arises when we have to
explain why, if this central substance is stimulated throughout,
_only_ arms and legs respond; in other words, why the toe-centre
“plays upon” the arm-centre, and not on the others? When a frog is
decapitated, if we gently touch one leg with the point of the scalpel,
the leg will move, but only this leg. Prick more forcibly, and both
legs will move. Keep on pricking, and all four legs are drawn up, and
the frog hops away. Each excitation was propagated along the cord;
but the discharge was restricted in the first case to one limb, in
the second to two, in the third it involved all the muscles of the
trunk. At the sight of a friend a dog wags his tail gently: as there
is no _direct_ connection between the optic nerves and the tail, this
playing of one centre on another must be by the agency of intermediate
centres; and we know that if the dog’s spinal cord be divided, this
excitation from the optic centre is no longer possible, yet the tail
will wag if the abdomen be tickled, or the leg pinched. Now compare the
effect on the dog produced by the sight of his master, or of a friend
accustomed to take him out. There is no longer a gentle wagging of the
tail, but an agitation of the whole body: he barks, leaps, and runs
about; the central stimulation is discharged through many outlets; and
could we test the effect, we should find an appreciable alteration
in the thermal and electrical condition of the whole organism, with
corresponding changes in circulation, secretion, etc. So different are
the consequences of two slightly different retinal impressions mingling
their stimulations with the same mass of central substance!
182. The discharge is determined by two conditions: the state of
tension, and the energy of the stimulation. _The state of tension is
increased by every stimulation which falls short of a discharge_; that
is to say, faint and frequent stimulation augments the excitability,
whereas powerful stimulation exhausts it. When, therefore, one
wave succeeds another in the same direction, it reaches a centre
more disposed to discharge; or, as Cayrade expresses it, “a certain
agitation of the cells is necessary for the manifestation of their
property of reaction, in the same way that the concentric circles
produced on the surface of water by a falling stone are more rapid and
more numerous if a stone has already agitated the surface.”
183. So much for the tension. What has been called the energy of the
stimulation is more complicated. It is not measurable as a simple
physical process; we cannot say that a given quantity of any external
force will determine a given discharge. It is mostly complicated by
psychical processes, and these so modify the result that instead of the
predicted discharge there is arrest, or discharge from another centre.
Press a dog’s skin with increasing violence, and the effect increases
from pleasurable to painful irritation; but whether the dog will cry
out and bite, or cry out and struggle to escape, depends upon whether
the pincher is a stranger or a friend. If you hurt a dog while removing
a thorn from its foot it will cry out, but although the pain causes it
to initiate a biting movement, by the time your hand is reached that
movement will have been changed, and the dog will lick the hand which
he knows is hurting him in the endeavor to relieve him of the thorn.
The co-operation of the mind is here evident enough. A purely psychical
process has interfered with the purely physiological process. And I
shall hereafter endeavor to show that psychical processes analogous in
kind though simpler in degree are really co-operant in actions of the
spinal cord. The dog would be said to discriminate between the pain
inflicted by a friend, and the same pain inflicted by a stranger. In
other words, the sensitive mechanism would be differently determined
in the direction of discharge, although the initial stimulation was the
same in each case. If we admit that the resulting action is in each
case the consequence of the particular group of elements co-operating,
there will be no ground for denying that analogous _discrimination_
is manifested by the brainless animal, who also responds differently
to different external stimuli, and differently to the same stimulus
under different central conditions. The brainless frog croaks if its
back be gently stroked with the handle of a scalpel; but if the point
be used, or if the handle be roughly pressed, instead of croaking,
the frog raises his leg in defence. Here the difference in the
peripheral irritation has excited a different reaction in the centre;
and this might be interpreted as purely physical; if now the leg be
fastened, and the movement of defence be thus prevented, the frog will
employ the other leg; or adopt some other means of relieving itself
from the irritation. It was a mass of registered experiences which
determined the dog not to bite his master. An analogous registration
of experiences determines the changed reactions of the brainless frog.
But this is a point which can only be touched on in passing here, and
it is touched on merely to facilitate our exposition of the complicated
conditions of neural discharge. These may be formulated in
184. LAW IV. The simultaneous influence of several stimuli, each
of which separately excites the same centre, is cumulative:
stimuli then assist each other, and their resultant is their
_arithmetical_ sum.
Simultaneous stimuli, each of which excites a different centre,
_interfere_ with each other’s energy, and their resultant is
their _algebraical_ sum.
In this law there is a condensed expression of that composition of
forces which may either result in Discharge or Arrest. By simultaneity
is not to be understood merely the coincidence of impressions, but also
the reverberations of impressions not yet neutralized by others. Thus
when Sensibility is tested by the now common method,[195] it is found
that if one leg is withdrawn after a lapse of, say, ten pendulum beats,
the other leg, which has not been irritated, will nevertheless, on
irritation, be withdrawn in less than ten beats, provided the central
agitation caused by the first stimulation has _not yet subsided_. But,
on the contrary, the withdrawal will be considerably deferred, or
even prevented altogether, if at the same time that the leg is acted
on by the acid, a more powerful excitation takes place in some other
part of the body. In the one experiment we see simultaneous excitation
in the same centre and the same direction. In the other simultaneous
excitation in different centres. The more powerful excitation
suppresses the discharge from the less powerful; but although it
prevails, it loses just as much force as it arrests.[196]
185. There is another very interesting experiment by Freusberg, which
must be cited here.[197] When the sciatic nerve is divided, the frog’s
leg is of course not withdrawn from the acidulated water, because in
that case no sensory excitation is propagated from the skin to the
centre; but although there is no stimulation from the skin, there is
one from the muscles, as appears in the fact that if a small weight be
suspended on this leg, the other leg is more rapidly withdrawn from the
acidulated water--the action of the muscles having affected the centre
and increased its excitability.
186. When the motor group of one leg is moderately stimulated, the
discharge is confined to the muscles of that one leg; and according
to Herzen the excitability of the motor group of the other leg is
thereby somewhat diminished. But if the stimulation be increased, there
is an irradiation to the other group, which irradiation, although
not sufficient to excite a discharge, renders it much more _ready_
to discharge, so that a feeble stimulus suffices. This accords with
Setschenow’s observations, and is confirmed by Freusberg’s experiment,
in which, when one leg was stimulated by acid, if the acid were not
wiped off but allowed to keep up the irritation, the other leg moved
without being irritated; and this other leg having come to rest, when
in its turn dipped in the acid, was more rapidly withdrawn than the
first leg had been on first being stimulated; showing that the central
groups had become more excitable by the stimulation of either leg.
187. While it is intelligible that an excitation of one group should
increase the activity of neighboring groups, by an increase of the
vascular activity of the region, it is not so readily intelligible why
the feebler excitation of one group should diminish the excitability of
its neighbor; yet the facts seem to warrant both statements.
188. The conditions which determine Discharge are obscure. We may,
however, say that anatomical and physiological data force the
conclusion that whenever the central tissue is powerfully stimulated
in any one part, there is either a discharge, or a greater tension
(tendency to discharge) in every other part; in consequence of
which, every fresh stimulus in the _same_ direction finds the parts
more prepared to react; while every fresh stimulus in a _contrary_
direction meets with a proportional resistance. Stated thus generally,
the principle is clear enough; but the immense complication of
stimulations, and the statical variableness of the organs, renders its
application to particular cases extremely obscure. Why does the ticking
of a clock arrest the attention, even with unpleasant obtrusiveness, at
one time, and presently afterwards cease to be heard at all? Why does
the cut of a knife cause intense pain, and a far greater cut received
during the heat and agitation of a quarrel pass unfelt? Why will the
same external force excite convulsions in all the muscles, and at
another time scarcely be distinguishable? These are consequences of the
temporary condition of the centres; but there are permanent conditions
which in some organisms determine equally variable results. Thus the
shock of terror which will simply agitate one person, will develop an
epileptic attack in another, and insanity in a third; just as exposure
to cold will in one person congest the liver, in another the lungs. A
loud and sudden sound causes winking in most persons, and in many a
sort of convulsive shock. The harsh noise of a file causes a shiver in
some persons, and in others “sets the teeth on edge,” while in others
it causes an increased flow of saliva.
189. Nerves and centres have different degrees of excitability. The
nerve-terminals in the skin are more sensitive to impressions than
those in the mucous membrane; those in the alimentary canal are more
sensitive than those in the peritoneum; and all nerve-terminals are
more sensitive than nerve-trunks. A touch on the surface of the larynx
will produce a cough, but the nerve-trunk itself may be pinched or
galvanized without producing any such reflex. Moreover, there is the
difference of grouping. If the skin of the abdomen be tickled, there
is a reflex on the adductor and extensor muscles of the leg; but these
movements are reversed if the skin of the back be tickled. Nor indeed
are these movements invariable in either case; the one series will
sometimes quite suddenly change to the other, if the irritation is kept
up. That one and the same stimulus applied to the same spot should now
excite this group and now the other, shows that _both_ motor groups
are affected, and that the discharge takes place from the one which at
the time being is in the highest tension. The alternation of tension
explains rhythmical discharge.
THE LAW OF ARREST.
190. The Law of Arrest is only another aspect of the Law of Discharge,
and may be regarded as the conflict of excitations. If a stranger
enters the room where a woman lies in labor, there will often be caused
a sudden cessation of the uterine contractions.[198] Again, every one
knows how the breathing and the beating of the heart are arrested by
the idea of danger. The arrest is in each of the three cases only
temporary, because when the shock of the new stimulus has caused its
discharge (arrest), the peripheral irritation which caused the former
discharges resumes its influence, and uterus, heart, and diaphragm
begin to move again, even more energetically. Note, moreover, that not
only will the cerebral excitation arrest the spinal discharge--an idea
check the contractions of the uterus or the heart--but the reverse
also takes place. The brain of the woman may be intently occupied with
some scheme for the education or welfare of her expected child, but no
sooner do the labor pains set in, than all these cerebral combinations
are arrested.
191. One sensation arrests another; one idea displaces another. If
the foreleg of a headless frog be irritated, the hind-leg will also
be moved by the stimulation; or _vice versa_. Here there has been a
propagation of the excitation in either direction. But if while the
legs are thus irritated, and the centres are ready to discharge,
another and more powerful irritation reach the centre--say by pinching
the skin of the back--there will be no discharge on the legs. If the
vagus be irritated, the heart is arrested; but this does not take place
if at the same time, or immediately before, the foot has been sharply
pinched. A few gentle taps on the abdomen suffice to stop the heart;
but if a drop of acid be previously placed on the skin, we tap in vain,
the heart continues to beat. Brown Séquard cites several cases in which
convulsions were arrested by irritation of sensitive surfaces;[199]
and Dr. Crichton Browne records a case of a patient in whom there was
abolition of spinal reflex, due to cerebral irritation: tickling the
soles of the feet, or pricking the toes, which normally excites reflex
movements, in this case excited none whatever. “This seems to prove
that nerve currents, set in motion by irritation of the brain, or some
of its convolutions, transmitted down the cord, may inhibit reflex
action.”[200] Examples might indefinitely be multiplied. Pinch the
skin of a rabbit between the eyes, and you will observe that pulse and
respiration are slackened; but if the tail, which is very sensitive,
be pinched, this slackening is only momentary, and is succeeded by a
quickening--unless the pain be great. Even the effect of intense pain
may be neutralized by stimulating the vagus--just as the effect of
stimulating the vagus may be neutralized by pain. Claude Bernard found
that having dropped ammonia on the eyelid of a dog, the pain caused a
convulsive closure of the lid; but on galvanizing the vagus, the lid
opened again, to be closed when the galvanism ceased.[201] When the
heart is beating faintly (as in syncope), any irritating vapor applied
to the nostrils will cause a more energetic pulsation; yet a very
irritating vapor lowers the action of the heart beating normally, and
will even arrest that of a rabbit. Over-stimulation has almost always
the opposite effect of moderate stimulation.
192. While there seems every reason to believe that an excitation
necessarily affects the whole cerebro-spinal axis, there is no doubt
that there is a certain restriction of this irradiation to definite
paths, i. e. the responsive discharge is confined to definite groups.
Some of these restrictions are connate pathways: we bring them with us
at birth; but most of them are pathways acquired after birth. The boy
who sheds tears at parting from his mother when he goes to school, will
shed no tears when he parts from her to go to college, nay, perhaps
will shed none when he parts from her forever: not that his love has
lessened, but that the idea of such expression of it as “unmanly” has
become an organized tendency and arrests the tears. A youth of southern
race, who has not learned to be ashamed of tears, weeps freely under
such circumstances.
193. The pathways organized at birth are not many. Examples are the
inspiration which follows expiration; the movements of coughing when
the larynx is tickled; the movements of swallowing, sneezing, etc. Even
these may be arrested for a brief time by what is called “the will”;
but when once the discharge begins in any part of the mechanism, the
whole group is necessarily involved and the action is then inevitable.
Many of the reflex actions which are universal are nevertheless
acquired. Winking, for instance, when an object approaches the eye, is
universal among us, but is never seen in infants, nor in animals. It
is even doubtful whether the drawing up of the leg when the toes are
pinched is not an acquired reflex. Doubtful, I mean, in this sense,
that although the fact of non-withdrawal is observable in infants, who
cannot localize their sensations, this may be due to the imperfect
development of their nervous system. Mr. Spalding has proved that
although the callow bird cannot fly, the mechanism of flight is no
sooner developed than the action follows at once, without any previous
tentative experiences.
194. By experience we learn to restrict the paths of irradiation,
so as to wink with one eye while the other is unmoved, to bend one
finger while the rest are extended, to move one limb, or one group of
muscles, while the others are at rest; in short, to execute any one
particular action, and not at the same time agitate superfluously many
other organs. The boy when first learning to write is unable to prevent
the simultaneous motions of tongue and legs, which are ludicrously
irrelevant to the purpose of writing; but he learns to keep all his
organs in subjection, and only the eyes and hands active.[202] An
analogous restriction takes place in thinking. A train of thought is
kept up by the exclusion of all suggestions which are not pertinent;
and the power of the thinker is precisely this power of concentration.
THE HYPOTHESIS OF INHIBITORY CENTRES.
195. The facts and their formulated laws which have just been adduced
furnish a sufficient explanation of all the phenomena of arrest
which of late years have been detached and assigned to a special
mechanism of inhibitory nerves and centres. In spite of the eminent
authorities countenancing the hypothesis of a particular set of
inhibitory nerves, and particular centres of inhibition, I must confess
that the hypothesis appears to me inadmissible; and that I side with
those physiologists who hold that each nerve and each centre has its
inhibitory action. Indeed, if the action of arrest be, as I maintain,
only another aspect of the action of discharge, the result of the
conflict of forces, to say that all centres have the property of
excitation, is to say that all have the properties of discharge and
arrest: the discharge is only the resultant of the conflict along the
line of least resistance; the arrest is the effect of the conflict
along the line of greatest resistance. The observed phenomena of
arrest are so varied and numerous that the upholders of the inhibitory
hypothesis have been forced to invent not only arresting centres,
but centres which arrest these arresting centres! Dr. Lauder Brunton
candidly remarks: “At present our notions of nervous action seem to be
getting as involved as the Ptolemaic system of astronomy, and just as
epicycles became heaped upon cycles, so nerve-centres are being added
to nerve-centres. And yet, clumsy though the system may be, it serves
at present a useful purpose, and may give real aid until a better
is discovered.” I do not think a Copernicus is needed to discover
a better. The Law of Arrest as a general neural law suffices, when
the right conception of a _centre_ as a physiological rather than an
anatomical designation is admitted. (See p. 173.)
196. It would be out of place here to consider the conflicting evidence
which at present renders the question of the movements of the heart
one of the most unsatisfactory in the whole range of experimental
physiology. After devoting much time to it, and after writing a long
chapter on it, I suppress what I had written, and content myself with
the statement that no advantage whatever is derived from the hypothesis
of a special mechanism of arrest, unless perhaps in giving a temporary
precision to the direction of research. I mean that the search for
special centres may lead to the discovery of the particular paths to
which an impulse is restricted in any one action: as, for instance,
the vagus in retarding the pulsation of the heart. If the cerebrum can
determine a movement, and combine various movements, it is a centre of
arrest; if the cerebellum can determine and regulate movements, it is a
centre of arrest; if the medulla oblongata can determine and regulate
movements, it is a centre of arrest; if the medulla spinalis can
determine and combine movements, it is a centre of arrest; if a nerve
can dilate a constricted blood-vessel, or constrict a dilated one, it
is a nerve of arrest. In other words, every centre exerts its action
either in discharging, or in arresting the discharge of some other
centre.
The physiological process of Arrest may be physically interpreted
as Interference;[203] not that the process in nerve-tissue is to be
understood as the _same_ as that observed in fluids, or that the
metaphor of neural waves is to be taken for more than an intelligible
picturing of the process; the difference in the two agents forbids our
admitting the resemblance to be more than analogical. Thus interpreted,
however, we see that not only will one centre arrest the action of
another, but one nerve may be made to arrest itself! I mean that, under
similar conditions of interference, the stimulation which normally
follows on external stimulus may be inhibited by a previous, or a
counter stimulation. Thus the nerve which will be stimulated by a
chemical or mechanical stimulus, wholly fails to react if a constant
current is passing through it, although this constant current does not
itself cause a constant contraction. Remove the electrodes, and then
the chemical or mechanical stimulus takes effect. Or the experiment
may be reversed: let the nerve be placed in a saline solution, and
the muscles will be at once thrown into violent contraction; if the
electrodes are now applied to the nerve, the contractions suddenly
cease, to begin again directly the electrodes are removed.
ANATOMICAL INTERPRETATION OF THE LAWS.
197. The problem for the anatomist is twofold: First, given the
organ, he has to determine its function, or _vice versa_, given the
part of an organ, to determine its functional relation; secondly,
given the function, he has to determine its organ. The structural
and functional relations of nerves and centres have been ascertained
in a general way; we are quite sure that the posterior nerves carry
excitations from sensitive surfaces, that the anterior nerves carry
excitations to muscles and glands; and that the central gray substance
not only reflects a sensory excitation as a motor excitation, but
propagates an excitation along the whole cerebro-spinal axis. But when
we come to a more minute analysis of the functional activities, and
endeavor to assign their respective values to each part of the organic
mechanism, the excessive complexity and delicacy of the mechanism
baffles research. We are forced to grope our way; and the light of the
hypothetic lamps which we hold aloft as often misdirects as helps us.
The imaginary anatomy which at present gains acceptance, no doubt seems
to simplify explanations; but this seeming turns out to be illusory
when closely examined. The imagined arrangement of fibres and cells
we have seen to be not in agreement with observation; and were it
demonstrable, it would not account for the laws of propagation. Suppose
sensory fibres to terminate in cells, and fibres from these to pass
_upwards_ to other sensory cells and _transversely_ to motor cells, how
in such a connected system could irradiations take place, if the law of
isolated conduction were true? And how could isolated conduction take
place, if the excitation of a part were necessarily the excitation of
the whole? Why, for example, is pain not always irradiated? Why is it
even localized in particular spots, determining movements in particular
muscles; and when irradiation takes place, why is it circumscribed,
or--and this is very noteworthy--manifested in two widely different
places, the intercostal and trigeminal nerves? Why does the irritation
of intestinal worms manifest itself now by troubles of vision, now by
noises in the ear, and now by convulsions?
198. Answers to such questions must be sought elsewhere. Our first
search should be directed to the anatomical data, which have hitherto
been so imprudently disregarded. Under the guidance of the laws
formulated in this chapter, let us accept the anatomical fact of a
vast network forming the ground-substance in which cells and fibres
are embedded, and with which they are continuous; let us accept the
physiological principle Of similarity of property with similarity
of composition and structure; let us accept the hypothesis that the
discharge of neural energy is dependent on the degree of stimulus
and the degree of tension at the time being--and we shall have at
least a general theory of the process, though there will still remain
great obscurities in particular applications. We shall have before
us a vast network of pathways, all equally capable of conducting an
excitation, but not all equally and at all moments open. It will always
be difficult to determine what are the conditions which at any moment
favor or obstruct particular openings. Paths that have been frequently
traversed will of course be more readily traversed again; but this very
facility will _sometimes_ be an obstacle, since it will have caused
that path to be preoccupied, or have fatigued the organ to which it
leads.
199. Since the escape of an excitation must always be along the lines
of least resistance, an obvious explanation of the restriction to
certain paths has been to assume that some fibres and cells have
naturally greater resistance than others. But this explanation is
simply a restatement of the fact in other words. What is this greater
resistance? Why is it present in one fibre rather than in another?
We should first have to settle whether the resistance was in the
nervous pathway itself, or in the centre, or in the organ innervated;
an excitation might pass along the nervous tract, yet fail to change
the state of the centre, or the organ, sufficiently to produce an
appreciable response; and only those parts where an appreciable
response was produced would then be considered as having had the
pathways of propagation open.
200. When we reflect on the innumerable stimulations to which the
organism is subjected from so many various points, and remember
further that _each stimulation leaves behind it a tremor which
does not immediately subside_, we shall conceive something of the
excessive complexity of the mechanism, and marvel how any order is
established in the chaos. What we must firmly establish in our minds
is that the mechanism is essentially a _fluctuating_ one, its elements
being combined, recombined, and resolved under infinite variations
of stimulation. If it were a mechanism of fixed relations, such as
we find in machines, or in the “mechanism of the heavens,” we might
accept the notion of certain organites having greater resistance as
a consequence of their structure, just as one muscle resists being
moved by the impulse which will move another. Nor is it doubtful
that such differences exist in nervous organites; but the laws of
central excitation are not interpretable by any such hypothesis,
since we know that the paths which were closed against an impulse of
considerable energy may be all open to an impulse of feebler energy,
and that a slight variation in the stimulus will be followed by a wide
irradiation. For example, a grain or two of snuff will excite the
violent and complex act of sneezing, but the nerves of the nasal cavity
may be pinched, cut, or rubbed, without producing any such result.
One group of nervous organites will fail to involve the activity of
neighboring groups; and the simple movement of a single organ is then
all that appreciably follows the stimulation; yet by a slight change in
the stimulation, the organites are somewhat differently grouped, and
the result is a complex movement of many organs. It is this fluctuation
of combination in the organites which renders education and progress
possible. Those combinations which have very frequently been repeated
acquire at last an automatic certainty.
* * * * *
We are now in a position to examine with more precision the extremely
important laws of nervous action which are involved in the phenomena
designated by the terms Reflex Action, Automatic Action, and Voluntary
Action.
PROBLEM III.
ANIMAL AUTOMATISM.
“L’organisme le plus complexe est un vaste mécanisme qui résulte de
l’assemblage de mécanismes secondaires.”--CLAUDE BERNARD.
“Les corps vivants sont machines à l’infini.”--LEIBNITZ.
“Noi lamentiamo con Majendie che nel linguaggio fisiologico siensi
intruse le preopinioni psicologiche col trascico inevitabile
del vocaboli, ai quali codeste preopinioni si trovano legate.
Probabilmente questa fu una delle principali cagioni degli errori e
degli equivoci anatomofisiologici, da cui non poterono svincolarsi,
a loro insaputa, i cultori sperimentali della scienza, perchè nell’
interpretare i fenomeni osservati erano obbligati ad usare il
linguaggio di una false moneta in corso.”--LUSSANA _e_ LEMOIGNE,
_Fisiologia dei Centri Nervosi_, 1871, I. 16.
ANIMAL AUTOMATISM.
CHAPTER I.
THE COURSE OF MODERN THOUGHT.
1. Modern Philosophy has moved along two increasingly divergent lines.
One, traversed by Galileo, Descartes, Newton, and Laplace, had for
its goal the absolute disengagement of the physical from the mental,
i. e. the objective from the subjective aspect of phenomena, so
that the physical universe, thus freed from all the complexities of
Feeling, might be interpreted in mechanical terms. As a preliminary
simplification of the problem this was indispensable; only by it
could the First Notion of primitive speculation be replaced by the
Theoretic Conception of scientific speculation.[204] The early
thinker inevitably invested all external objects with properties and
qualities similar to those he assigned to human beings, and their
actions he assigned to human motives. Sun, moon, and stars seemed
living beings; flames, streams, and winds were supposed to be moved
by feelings such as those known to move animals and men. Nor was any
other conception then possible: men could only interpret the unknown
by the known, and their standard of all action was necessarily drawn
from their own actions. Not having analyzed Volition and Emotion,
above all not having localized these in a neuro-muscular system, men
could not suspect that the movements of planets and plants, and of
streams and stones, had motors of a different kind from the movements
of animals. The scientific conception of inert insensible Matter was
only attained through a long education in abstraction; and is assuredly
never attained by animals, or by savages. But no sooner were vital
conditions recognized, than the difference between vital and mechanical
movements emerged. When men learned that many of their own actions
were unaccompanied either by Love or Hate, by Pleasure or Pain, and
that many were unprompted by conscious intention, while others were
unaccompanied by conscious sensation, they easily concluded that
wherever the special conditions of Feeling were absent, the actions
must have some other motors. Intelligence, Emotion, Volition, and
Sensation being one by one stripped away from all but a particular
class of bodies, nothing remained for the other bodies but insensible
Matter and Motion. This was the Theoretic Conception which science
substituted for the First Notion. It was aided by the observation
of the misleading tendency of interpreting physical phenomena by
the human standard, substituting our fancies in the place of facts,
manipulating the order of the universe according to our imagination
of what it might be, or ought to be. Hence the vigilance of the new
school in suppressing everything pertaining to the subjective aspect
of phenomena, and the insistance on a purely objective classification,
so that by this means we might attain to a knowledge of things as they
are. By thus withdrawing Life and Mind from Nature, and regarding
the universe solely in the light of Motion and the laws of Motion,
two great scientific ends were furthered, namely, a classification
of conceptions, and a precision of terms. Objective phenomena made a
class apart, and the great aim of research was to find a mathematical
expression for all varieties under this class. Masses were conceived
as aggregates of Atoms, and these were reduced to mathematical points.
Forces were only different modes of Motion. All the numberless
differences which perception recognized as _qualities_ in things, were
reduced to mere variations in _quantity_. Thus all that was particular
and concrete became resolved by analysis into what was general and
abstract. The Cosmos then only presented a problem of Mechanics.
2. During this evolution, the old Dualism (which conceived a material
universe sharply demarcated from the mental universe) kept its
ground, and attained even greater precision. The logical distinction
between Matter and Mind was accepted as an essential distinction,
i. e. representing distinct reals. There was on the one side a group
of phenomena, Matter and Force; on the other side an unallied group,
Feeling and Thought: between them an impassable gulf. How the two
were brought into relation, each acting and reacting on the other,
was dismissed as an “insoluble mystery”--or relegated to Metaphysics
for such minds as chose to puzzle over questions not amenable to
experiment. Physics, confident in the possession of mathematical
and experimental methods which yielded definite answers to properly
restricted questions, peremptorily refused to listen to any suggestion
of the kind. And the career of Physics was so triumphant that success
seemed to justify its indifference.
3. In our own day this analytical school has begun to extend its
methods even to the mental group. Having reduced all the objective
group to mathematical treatment, it now tries to bring the subjective
group also within its range. Not only has there been more than one
attempt at a mathematical Psychology; but also attempts to reduce
Sensibility, in its subjective no less than in its objective aspect, to
molecular movement. Here also the facts of Quality are translated into
facts of Quantity; and all diversities of Feeling are interpreted as
simply quantitative differences.
4. Thus far the one school. But while this Theoretic Conception
stripped Nature of consciousness, motive, and passion, rendering it a
mere aggregate of mathematical relations, a critical process was going
on, which, analyzing the nature of Perception, was rapidly moving
towards another goal. Locke, Berkeley, Hume, and Kant, directing their
analysis exclusively to the subjective aspect of phenomena, soon broke
down the barriers between the physical and mental, and gradually merged
the former in the latter. Matter and its qualities, hitherto accepted
as independent realities, existing where no Mind perceived them, were
now viewed as the creations of Mind--their existence was limited to a
state of the percipient. The old Dualism was replaced by Idealism. The
Cosmos, instead of presenting a problem of Mechanics, now presented a
problem of Psychology. Beginning with what are called the secondary
qualities of Matter, the psychological analysis resolved these into
modes of Feeling. “The heat which the vulgar imagine to be in the fire
and the color they imagine in the rose are not there at all, but are in
us--mere states of our organism.” Having gained this standing-place,
there was no difficulty in extending the view from the secondary to the
primary qualities. These also were perceptions, and only existed in
the percipient. Nothing then remained of Matter save the hypothetical
unknown _x_--the postulate of speculation. Kant seemed forever to have
closed the door against the real Cosmos when he transformed it into
a group of mental forms--Time, Space, Causality, Quantity, etc. He
propounded what may be called a theory of mental Dioptrics whereby a
pictured universe became possible, as Experience by its own _a priori_
laws moulded _itself_ into a consistent group of appearances, which
produced the illusion of being a group of realities. He admitted,
indeed, that by the operation of Causality we are compelled to believe
in a Real underlying the appearances; but the very fact that this
Causality is a _subjective law_, is proof, he said, of its not being
an _objective truth_. Thus the aim of the mechanical conception was
to free research from the misleading complexities of subjective
adulterations, and view _things as they are_ apart from their
_appearances_; but this aim seemed illusory when Psychology showed that
Time, Space, Matter, and Motion were themselves not objective reals
except in so far as they represented subjective necessities; and that,
in short, things _are_ just what they _appear_, since it is only in the
relation of external reals to internal feelings that objects exist for
us.
5. Idealism has been the outcome of the psychological method. It
has been of immense service in rectifying the dualistic conception,
and in correcting the mechanical conception. It has restored the
subjective factor, which the mechanical conception had eliminated.
It has brought into incomparable clearness the fundamental fact that
all our knowledge _springs from_, and is _limited by_, Feeling. It
has shown that the universe represented in that knowledge, can only
be a picture of the system of things as these exist in relation to
our Sensibility. But equally with the mechanical conception it has
erred by incomplete analysis. For a complete theory of the universe,
or of any one phenomenon, those elementary conditions which analysis
has provisionally set aside must finally be restored. When Quality
is replaced by Quantity, this is an artifice of method, which does
not really correspond with fact. The quality is the fact given in
feeling, which we analytically refer to quantitative differences,
but which can never be wholly resolved into them, since it must be
presupposed throughout. One color, for example, may be distinguished
from another as having more or fewer undulations; and so we may by
abstraction, letting drop all qualitative characters, make a scale
of undulations to represent the scale of colors. But this is an
ideal figment. It is the representation of one series of feelings by
another series of different feelings. No variation of undulations will
really correspond with variation in color, unless we reintroduce the
suppressed _quality_ which runs through all color. Attempt to make one
born blind feel, or even understand, Color by describing to him the
kind of wave-movement which it is said to be, and the vanity of the
effort will be manifest. Movement he knows, and varieties of movement
as given in _tactile and muscular sensations_; but no combination and
manipulation of such experiences can give him the specific sensation
of Color. That is a purely subjective state, which he is incapable of
experiencing, simply because one of the essential factors is absent.
One set of objective conditions is present, but the other set (his
sense-organ) is defective. Without the “greeting of the spirit”
undulations cannot become colors (nor even undulations, for these
also are forms of feeling). Besides the sense-organ there is needed
the feeling of Difference, which is itself the product of past and
present feelings. The reproduction of other colors, or other shades of
color, is necessary to this perception of difference; and this involves
the element of Likeness and Unlikeness between what is produced and
reproduced. So that a certain mental co-operation is requisite even for
the simplest perception of quality. In fact, psychological analysis
shows that even Motion and Quantity, the two objective terms to which
subjective Quality is reduced, are themselves Fundamental Signatures
of Feeling;[205] so that here, as elsewhere, it is only by analytical
artifice that the objective can be divorced from the subjective. Matter
_is_ for us the Felt; its Qualities are differences of Feeling.
6. Not that this result is to be interpreted as freeing our Theoretic
Conception from its objective side, and landing us in Idealism,
which suppresses the real universe. The denial of all reality apart
from our minds, is a twofold mistake: it confounds the conception of
general relations with particular relations, declaring that because
the External in its relation to the sentient organism can only be
what it is felt to be, therefore it can have no _other_ relations to
other individual reals. This is the first mistake. The second is the
disregard of the constant presence of the objective real in every fact
of Feeling: the Not-Self is emphatically present in every consciousness
of Self.
The legitimate conclusion is neither that of Dualism nor of Idealism,
but what I have named Reasoned Realism (_Problems_, Vol. I. p. 201),
which reconciles Common Sense with Speculative Logic, by showing that
although the _truth_ of things (their _Wahrheit_) is just what we
perceive in them (our _Wahrnehmung_), yet their _reality_ is this, and
much more than this. _Things_ are what they are felt to be; and what
they are thought to be, when thoughts are symbols of the perceptions.
Idealism declares that they are _nothing but_ this. It is against this
_nothing but_ that Common Sense protests; and the protest is justified
by Reasoned Realism, which, taking a comprehensive survey of the facts,
thus answers the idealist: “Your synthesis is imperfect, since it
does not include _all_ the data--notably it excludes the fact of an
objective or Not-Self element in every feeling. You may, conceivably,
regard the whole universe as nothing but a series of changes in your
consciousness; but you cannot hope to convince me that I myself am
simply a change in yourself, or that my body is only a fleeting image
in your mind. Hence although I conclude that the Not-Self is to you, as
to me, undivorceable from Self, inalienable from Feeling, in so far as
it is felt, yet there must nevertheless be for both of us an existence
not wholly coextensive with our own. _My_ world may be my picture of
it; _your_ world may be your picture of it; but there is something
common to both which is more than either--an existent which has
different relations to each. _You_ are not _me_, nor is the pictured
Cosmos _me_, although I picture it. Looking at you and it, I see a vast
whole of which you are a small part; and such a part I conclude myself
to be. It is at once a picture and the pictured; at once subjective and
objective. To me all your modes of existence are objective aspects,
which, drawing from my own experience, I believe to have corresponding
subjective aspects; so that your emotions, which to me are purely
physical facts, are to you purely mental facts. And psychological
analysis assures me that all _physical facts are mental facts expressed
in objective terms_, and _mental facts are physical facts expressed in
subjective terms_.”
7. But while Philosophy thus replaces the conceptions of Dualism and
Idealism by the conception of the Two-fold Aspect, the special sciences
in their analytical career have disregarded the problem altogether.
The mechanical theory of the universe not only simplified research by
confining itself solely to the objective aspect of phenomena, but by
a further simplification set aside all vital and chemical relations,
to deal exclusively with mechanical relations. In ascertaining the
mathematical relations of the planetary system, no elucidation could
possibly be gained from biological or chemical conceptions; the
planets therefore were provisionally stripped of everything not
mechanical. In systematizing the laws of motion, it was necessary to
disengage the abstract relations from everything in any way resembling
spontaneity, or extra-mechanical agency: Matter was therefore, by
a bold fiction, declared to be inert, and its Motion regarded as
something superadded from without.
7_a_. And this was indispensable for the construction of those ideal
laws which are the objects of scientific research. Science, as we often
say, is the systematization of Experience under the forms of ideal
constructions. Experience implies Feeling, and certain fundamental
Signatures, all reducible to the primary discernment of Likeness and
Unlikeness. Hence Science is first a _classification_ of qualities
or discerned likenesses and differences; next a _measurement_
of quantities of discerned likenesses and differences. Although
measurement is itself a species of classification, it is distinguished
by the adoption of a standard unit of comparison, which, being precise
and unvarying, enables us to express the comparisons in precise and
unvarying symbols. Whether the unit of length adopted be an inch, a
foot, a yard, a mile, the distance of the earth from the sun, or the
distances of the fixed stars, the quantities thus measured are symbols
admitting of one invariable interpretation. The exactness of the
mathematical sciences is just this precision and invariability of their
symbols, and is not, as commonly supposed, the source of any superior
certainty as to the facts. The classificatory sciences, which deal with
qualities rather than with quantities, may be equally _certain_, and
represent fuller _knowledge_, because involving more varied feelings,
but they cannot pretend to exactness. Even on the quantitative side,
certainty is not identical with exactness. I may be quite certain that
one block of marble is larger than another--meaning that it affects
me more voluminously--but I cannot know how much larger it is, without
interpreting my feelings by the standard of quantity--the how-muchness
as represented by that standard. The immense advantages of exact
measurement need not be insisted on. The Biological Sciences, which
are predominantly classificatory, can never rival the Cosmological
Sciences in exactness; but they may reach a fuller knowledge; and
their certainty will assume more and more the character of exactness
as methods of measurement are applied to their classifications of
qualities. The qualitative and quantitative aspects of phenomena are
handled by the two great instruments, Logic and Mathematics, the second
being only a special form of the first. These determine the general
conceptions which are derived from our perceptions, and the whole
constitute Experience.
8. What is the conclusion to which these considerations lead? It
is that the separation of the quantitative from the qualitative
aspect of phenomena--the objective mechanical from the subjective
psychological--is a logical artifice indispensable to research; but
it is only an artifice.[206] In pursuance of this artifice, each
special science must be regarded as the search after special analytical
results; and meanwhile this method should be respected, and no
confusion of the boundaries between one science and another should be
suffered. Mechanical problems must not be confused by the introduction
of biological relations. Biological problems must not be restricted
to mechanical relations. I do not mean that the mechanical relations
present in biological phenomena are not to be sought, and, when found,
to be expressed in mechanical terms; I mean that such an inquiry must
be strictly limited to mechanical relations. Subjective relations
are not to be denied, because they are provisionally set aside, in an
inquiry into objective relations; but we must carefully distinguish
which of the two orders we are treating of, and express each in its
appropriate terms. This is constantly neglected. For example, nothing
is more common than to meet such a phrase as this: “A _sensory
impression_ is transmitted as a _wave_ of _motion_ to the brain, and
there being transformed into a state of _consciousness_, is again
reflected as a _motor_ impulse.”
The several sciences having attained certain analytical results, it
remains for Philosophy to co-ordinate these into a doctrine which will
furnish general conceptions of the World, Man, and Society. On the
analytical side a mechanical theory of the universe might be perfected,
but it would still only be a theory of mechanical relations, leaving
all other relations to be expressed in other terms. We cannot accept
the statement of Descartes that Nature is a vast mechanism, and Science
the universal application of mathematics. The equation of a sphere,
however valuable from a geometrical point of view, is useless as an
explanation of the nature and properties of the spherical body in
other relations. And so a complete theory of the mechanical relations
of the organism, however valuable in itself, would be worthless in
the solution of a biological problem, unless supplemented by all that
mechanical terms are incompetent to express.
9. The course of biological speculation has been similar to the
cosmological. It also began with a First Notion, which compendiously
expressed the facts of Experience. Nor can any Theoretic Conception be
finally adopted which does away with these facts, known with positive
certainty, and popularly expressed in the phrase: “I have a body, and
a soul.” We may alter the phrase either into “I _am_ a body, and I
_am_ a soul”; or into, “My body is only the manifestation of my soul”;
or, “My soul is only a function of my body”; but the fundamental
experiences which are thus expressed are of absolute authority, no
matter how they may be interpreted. That I have a body, or am a body,
is not to be speculatively argued away. That I move my arm to strike
the man who has offended me, or stretch out my hand to seize the fruit
which I see, is unquestionable; that these movements are determined by
these feelings, and are never thus effected unless thus determined, is
also unquestionable. Here are two sets of phenomena, having well-marked
differences of aspect; and they are grouped respectively under two
general heads, Life and Mind. Life is assigned to the physical
organism, or Body--all its phenomena are objective. Mind is assigned
to the psychical organism, or Soul--all its phenomena are subjective.
Although what is called my Body is shown to be a group of qualities
which are feelings--its color, form, solidity, position, motion--all
its physical attributes being what is felt by us in consequence of
the laws of our organization; yet inasmuch as these feelings have the
characteristic marks of objectivity, and are thereby referred to some
objective existence, we draw a broad line of demarcation between them
and other feelings having the characteristic marks of subjectivity,
and referring to ourselves as subjects. Psychological analysis shows
us that this line of demarcation is artificial, only representing a
diversity of aspect; but as such it is indispensable to science. We
cannot really separate in a sensation what is objective from what
is subjective, and say how much belongs to the Cosmos apart from
Sensibility, and how much to the subject pure and simple; we can only
view the sensation alternately in its objective and subjective aspects.
What belongs to extra-mental existence in the phenomenon of Color,
and what to the “greeting of the spirit,” is utterly beyond human
knowledge: for the ethereal undulations which physicists presuppose as
the cosmic condition are themselves subjected to this same greeting of
the spirit: they too are ideal forms of sensible experiences.
10. This conclusion, however, was very slowly reached. The distinction
of aspects was made the ground of a corresponding distinction in
agencies. Each group was personified and isolated. The one group was
personified in Spirit--an existent in every respect opposed to Matter,
which was the existent represented in the other group. One was said
to be simple, indestructible; the other compound, destructible. One
was invisible, impalpable, beyond the grasp of Sense; the other was
visible, tangible, sensible. One was of heaven, the other of earth.
Thus a biological Dualism, analogous to the cosmological, replaced
the First Notion. It was undermined by advances in two directions.
Psychology began to disclose that our conception of Matter was,
to say the least, _saturated_ with Mind, its Atoms confessedly
being ideal figments; and that all the terms by which we expressed
_material qualities_ were terms which expressed _modes of Feeling_;
so that whatever remained over and above this was the unknown _x_,
which speculation required as a postulate. Idealism, rejecting this
postulate, declared that Matter was simply the projection of Mind, and
that our Body was the objectivation of our Soul. Physiology began to
disclose that all the mental processes were (mathematically speaking)
_functions_ of physical processes, i. e. varying with the variations
of bodily states; and this was declared enough to banish forever the
conception of a Soul, except as a term simply expressing certain
functions.
11. Idealism and Materialism are equally destructive of Dualism. The
defects of particular idealist and materialist theories we will
not here touch upon; they mainly result from defects of Method. Not
sufficiently recognizing the primary fact testified by Consciousness,
namely, that Experience expresses both physical and mental aspects,
and that a Not-Self is everywhere indissolubly interwoven with Self,
an objective factor with a subjective factor, the idealist reduces
Existence to a mere panorama of mental states, and the Body to a
group in this panorama. He is thus incapable of giving a satisfactory
explanation of all the objective phenomena which do not follow in the
same order as his feelings, which manifest a succession unlike his
expectation, and which he cannot class under the order of his mental
states hitherto experienced. He conceives that it is the Mind which
_prescribes_ the order in Things; whereas experience assures us that
the order is _described_, not prescribed by us: described in terms of
Feeling, but determined by the laws of Things, i. e. the genesis of
subjective phenomena is determined by the action of the Cosmos on our
Sensibility, and the reaction of our Sensibility. He overlooks the
evidence that the mental forms or laws of thought which determine the
character of particular experiences, were themselves evolved through a
continual action and reaction of the Cosmos and the Soul, precisely as
the laws of organic action which determine the character of particular
functions were evolved through a continual adaptation of the organism
to the medium. These immanent laws are declared to be transcendental,
antecedent to all such action and reaction.
A similar exclusiveness vitiates the materialist doctrine. Overlooking
the primary fact that Feeling is indissolubly interwoven with processes
regarded as purely physical because they are considered solely in their
objective aspect, the materialist fails to recognize the operation of
psychological laws in the determination of physiological results;
he hopes to reduce Biology to a problem of Mechanics. But Vitality
and Sensibility are coefficients which must render the mechanical
problem insoluble, if only on the ground that mechanical principles
have reference to quantitative relations, whereas vital relations are
qualitative. His error is the obverse of the vitalist’s error. The
vitalist imagines that the speciality of organic phenomena proves the
existence of a cause which has no community with the forces operating
elsewhere; so, turning his back on all the evidence, he attempts to
explain organic phenomena without any aid from Physics and Chemistry.
The materialist, turning his back on all the evidence of quite special
conditions only found at work in living organisms, tries to explain
the problem solely by the aid of Physics and Chemistry. It is quite
certain that physiological and psychological problems are not to be
solved if we disregard the laws of Evolution through Epigenesis. The
mental structure is evolved, as the physical structure is evolved. It
is quite certain that no such evolution is visible in anorganisms,
nor will any one suppose it to be possible in machines. From the
biological point of view we must therefore reject both Idealism and
Materialism. We applaud the one when it says, “Don’t confuse mental
facts by the introduction of physical hypotheses”; and the other when
it says, “Don’t darken physical facts with metaphysical mists.” We say
to both, “By all means make clear to yourselves which aspect of the
phenomena you are dealing with, and express each in its own terms. But
in endeavoring to understand a phenomenon you must take into account
all its ascertainable conditions. Now these conditions are sometimes
only approachable from the objective side; at other times only from the
subjective side.”
12. While it is necessary to keep the investigation of a process on its
objective side, limited to objective conditions, and to express the
result in objective terms, we must remember that this is an artifice;
above all, we must remember that even within the objective limits our
analyses are only provisional, and must be finally rectified by a
restoration of all the elements we have provisionally set aside. Thus
rectified, the objective interpretation of vital and mental phenomena
has the incomparable advantage of simplifying research, keeping it
fixed on physical processes, instead of being perturbed by suggestions
of metaphysical processes. And as all physical investigation naturally
tends to reduce itself to a mechanical investigation, because Mechanics
is the science of motion, and all physical processes are motions,
we may be asked, Why should not the mechanical point of view be the
rational standing-point of the biologist? Our answer is, Because
Mechanics concerns itself with abstract relations, and treats of
products without reference to modes of production, i. e. with motions
without reference to all the conditions on which they depend. Every
physical change, if expressed in physical terms, is a change of
position, and is determined by some preceding change of position. It
is a movement having a certain velocity and direction, which velocity
and direction are determined by the velocity and direction of a force
(a pressure or a tension) compounded with the forces of resistance,
i. e. counter-pressures. Clearly, the nature of the forces in operation
must be taken into account; and it is this which the mechanical view
disregards, the biological regards. The mechanical view is fixed
on the ascertained adjustment of the parts, so that the working of
the organism may be explained as if it were a machine, a movement
here liberating a movement there. The biological view includes this
adjustment of parts, but takes in also the conditions of molecular
change in the parts on which the adjustment dynamically depends.
Mechanical actions may be expressed as the enlargement or diminution
of the angle of two levers; but chemical actions are not thus
expressible; still less vital and mental actions.
13. The organism is on the physical side a mechanism, and so long
as the mechanical interpretation of organic phenomena is confined
to expressing the mechanical principles involved in the mechanical
relations, it is eminently to be applauded. But the organism is
something more than a mechanism, even on the physical side; or, since
this statement may be misunderstood, let me say, what no one will
dispute, that the organism is a mechanism of a very special kind, in
many cardinal points unlike all machines. This difference of kind
brings with it a difference of causal conditions. In so far as the
actions of this mechanism are those of a dependent sequence of material
positions, they are actions expressible in mechanical terms; but in
so far as these actions are dependent on vital processes, they are
not expressible in mechanical terms. Vital facts, especially facts
of sensibility, have factors neither discernible in machines nor
expressible in mechanical terms. We cannot ignore them, although for
analytical purposes we may provisionally set them aside.
* * * * *
In the course of the development of the mechanical theory, the history
of which has just been briefly sketched, biological problems have more
and more come under its influence. There has always been a fierce
resistance to the attempt to explain vital and sentient phenomena
on mechanical, or even physical principles, but still the question
has incessantly recurred, How far is the organism mechanically
interpretable? And while the progress of Biology has shown more and
more the machine-like adjustment of the several parts of which the
organism is composed, it has also shown more and more the intervention
of conditions not mechanically interpretable. We shall have to
consider the question, therefore, under two forms. First, whether
animals are machines, and if not, by what characters do we distinguish
them from machines? Secondly, in what sense can we correctly speak of
Feeling as an agent in organic processes?
CHAPTER II.
THE VITAL MECHANISM.
14. No answer can be successfully attempted in reply to the first
of the questions which closed the last chapter until we have given
precision to certain terms of incessant recurrence. I have often
to remark on the peculiar misfortune of Psychology, that all its
principal terms are employed by different writers, and are understood
by different readers, in widely different senses: they denote and
connote meanings of various significance. All physicists mean the same
thing when they speak of weight, mass, momentum, electricity, heat,
etc. All chemists mean the same thing when they speak of affinity,
decomposition, oxygen, carbonic acid, etc. All physiologists mean the
same thing when they speak of muscle, nerve, nutrition, secretion, etc.
But scarcely any two psychologists mean precisely the same thing when
they speak of sensation, feeling, thought, volition, consciousness,
etc.; and the differences of denotation and connotation in their uses
of such terms lead to endless misunderstanding. As Rousseau says: “Les
définitions pourraient être bonnes si l’on n’employait pas les mots
pour les faire.” But since we must employ words as our signs, our
utmost care should be given to clearly marking what it is the signs
signify.
15. The question we have now before us, whether animal actions are
interpretable on purely mechanical principles? can only be answered
after a preliminary settlement of the terms. The first of these
terms to be settled is that of mechanism, when applied to the vital
organism. If the organism is a mechanism, its actions must of course be
interpretable on mechanical principles. But this general truth requires
a special interpretation, if on inquiry we find that the organism is a
particular kind of mechanism, one which is _not_ to be classed under
the same head as inorganic machines. And this we do find. In Problem
I. § 22, will be found a statement of the radical difference between
organic and inorganic mechanisms, due to the differences in their
structures. But the differences there noted do not affect the operation
of abstract mechanical principles, which are of course manifested
_wherever_ there is a dependent sequence of material changes; and which
are the same abstract principles in the mechanism of the heavens,
the mechanism of a paper-mill, or the mechanism of an animal body.
In other words, the principles are abstract, and are abstracted from
all concrete cases by letting drop what is special to each case,
retaining only what is common to all. This procedure is indispensable
to the ideal constructions of Science. But we cannot rightly interpret
any concrete case by abstract principles alone; we must restore the
special characters which the abstraction has eliminated. The most lucid
explanation of the mechanism of the heavens will leave us quite in
the dark respecting the action of a paper-mill, until we have studied
the mill at work, ascertained its structure and mode of operation,
and therein detected what is common both to its mechanism and to the
mechanism of the heavens. Thus equipped, we approach the study of
the animal mechanism, but find ourselves wholly in the dark until we
have also ascertained its structure and mode of operation; then we
may recognize in it the principles of dependent sequence which had
been abstracted from the paper-mill and the heavens. To neglect this
concrete study, and to argue from Machinery to Life in disregard
of special conditions, is not more rational than to assume that the
movement of a piston is prompted by volition.
16. The recognition of special differences is no denial of fundamental
identities. We do not deny the presence of phenomena in organisms
which belong to physical and chemical agencies, but we assert that
organisms have other phenomena besides these, dependent on conditions
not present in physical and chemical phenomena. The same material
elements and forces may be recognized in a moving inorganic body,
and a moving organic body; but in the latter there is a speciality
of combination with a speciality of result. Just as the same words
and laws of grammatical construction may be recognized in prose and
poetry; yet poetry is not prose, but has special rules of its own,
and special effects. In an organism, as in a machine, the adjustment
of the parts is a condition of the mechanical action; the one enables
us to explain the other. But the parts adjusted, and the consequences
of the adjustment, are unlike in the two cases. This unlikeness is
pervading and profound. One cardinal difference is that the combination
of the parts is in the machine a fixed, in the organism a fluctuating
adjustment; and this fluctuation is due to certain vital processes
subjectively known as _sensitive guidance_. Hence machines have fixed
and calculated mechanisms; whereas organisms are variable and to a
great extent incalculable mechanisms.
17. I conceive, therefore, that a theory which reduces vital activities
to purely physical processes is self-condemned. Not that we are
to admit the agency of any extra-organic principle, such as the
hypothesis of Vitalism assumes (Prob. I. § 14); but only the agency
of an intra-organic principle, or the abstract symbol of _all_ the
co-operant conditions--the special combination of forces which result
in organization. This assures us that an organism is a peculiar kind
of mechanism, the processes in which are peculiar to it; and among
those processes there is one which results in what we call Sensibility.
This Sensibility is a factor which raises the phenomena into another
order. To overlook its presence is fatal to any explanation of the
organic mechanism. Yet it is overlooked by those who tell us that
when an impression on a nerve is conveyed to the brain, and is thence
reflected on the limbs--as when the retina of a wolf is stimulated
by the image of a sheep, and the spring of the wolf upon the sheep
follows as a “purely mechanical consequence--the whole process has
from first to last been physical.” Unless the term _physical_ is
here used to designate the _objective sequence_, as contemplated by
an onlooker, who likens the process to the sequence observable in a
machine, I should say that from first to last the process has been
_not_ physical, but _vital_, involving among its essential conditions
the peculiarly vital factor named Sensibility. The process taking place
in the wolf’s organism is one which involves conditions never found in
purely physical processes. We may indeed analytically disregard these.
We may view the process in its purely physical relations, or in its
purely chemical relations, or in its purely mathematical (mechanical)
relations. But this is the artifice of the analytical method. In
reality the process is no one of these, for it is all of these; it is a
process in a living organism, and depends on conditions only found in
living organisms--nay, in this particular case the process depends on
conditions only found in organisms like that of the wolf; for the image
of the sheep will stimulate the brain of a goat, horse, or elephant
without producing any such movement in the organism.
18. The importance of this point must excuse my reiteration of
it. We must make clear to ourselves that the organism is in its
objective aspect a physiological mechanism, in its subjective aspect
a psychological mechanism: in both aspects it is to be radically
demarcated from all inorganic mechanisms. In it the combination
and co-ordination of movements involve conditions never present
in machines; among these conditions, there are combinations and
co-ordinations of Sensibility, which, although material processes
on the objective side, are processes believed to be only present in
organisms. We have the strongest reasons for concluding that every
feeling, every change in Sensibility, has its correlative material
process in the organism--is, in short, only the subjective aspect
of the objective organic change. What in Physiology is called
Co-ordination and has reference to movements, in Psychology may be
called Logic, having reference to feelings. But be this latter point
accepted or rejected, the one point which admits of no dispute is
that an organism is radically distinguishable from every inorganic
mechanism in that _it acquires through the very exercise of its primary
constitution, a new constitution with new powers_. Its adjustment is a
changing and developing mechanism. That is to say, a machine, however
complex its structure, is constructed once for all, and this primary
constitution is final, the adjustment of parts remaining unaltered;
and although by exercise the machine may come to work more easily,
with less friction, it never comes to work differently, to _readjust_
its parts, and develop new capabilities. It has no _historical_ factor
manifest in its functions. It has no experience. It reacts at last
as at first. How different the organism! This has not only variable
adjustments due to internal fluctuations, it has experience which
develops new parts, and new adjustments of old parts. Every organism
has its _primary_ constitution in the adjustment of parts peculiar to
the species; it has also its _secondary_ or modified constitution,
in the adjustment which has been more or less altered by individual
experiences; it has, thirdly, its _temporary_ constitution in the
variable adjustment due to the varying state of tension which results
from varying stimulation.
19. A word on each. There is a structural disposition of the parts
which is common to large groups of organisms, so that a corresponding
similarity is observable in the reactions of these organisms. Thus all
quadrupeds use their limbs for locomotion in very similar ways; birds
use their wings for flight in similar ways. All vertebrates swallow
their food, defend themselves, shrink when hurt, etc., in ways that are
very similar. In so far as their organizations are alike, their actions
and reactions are alike. In so far as their organizations differ, their
actions and reactions differ. The goose and the vulture are alike in
the main lines of structure; still more alike are duck and hen; yet,
owing to certain unlike characters of structure, they manifest some
marked differences in action and reaction: the goose will starve in
the presence of food which the vulture gluttonously devours, and the
vulture will refuse the vegetable food which the goose devours; the
duck plunges into the water, the hen not only refuses to enter it,
but is greatly agitated when she sees the ducklings she has hatched
plunging into it. That peculiar instincts, habits, and feelings are
rigorously determined by peculiarities in the organism, no one doubts,
when animals are in question. If this is less obvious in the case of
men, the reason is that there the influence of other factors somewhat
masks the operation of the primary constitution--these factors are the
modified and the temporary constitutions. Yet even in man it is true to
say that his feelings and actions are the result of his organization,
native and acquired.
20. No two men are organized in all respects alike. There are
individual variations in structure, both native and acquired. These may
be too slight to be appreciable by any other test than the difference
of reaction under similar external stimuli; but the variations in the
sensibility to music, color, temperature, sexual influence, moral
influence, etc., betray corresponding differences in the organisms.
Any one variation in structure, seemingly trivial, may be the origin
of well-marked diversity in physical and moral characters. Compare
the bull with the ox, or the predatory aggressive eagle with the
cowardly vulture. Nor are the temporary modifications to be overlooked.
Antoine Cros mentions the case of a patient, a young girl, suffering
from congested liver and spleen, which of course altered the state
of her blood, and thus for a time modified her constitution. Her
moral character was greatly altered by it. She ceased to feel any
affection for father or mother; would play with her doll, but could
not be brought to show any delight in it; could not be drawn out of
her apathetic sadness. Things which previously had made her shriek
with laughter, now left her uninterested. Her temper changed, became
capricious and violent.[207] Congestion of the lungs, if unaccompanied
by congestion of the liver, never produces such effects, because not
thus altering the blood. The effects of liver congestion are familiar.
Cros cites the case of a magistrate whose liver was enlarged, and whose
skin showed a markedly bilious aspect, and in whom all affection seemed
to be dead: he did not exhibit any perversion or violence, only want
of emotive reaction. If he went to the theatre he could not feel the
slightest pleasure in it. The thoughts of his home, his absent wife
and children, were, he declared, as unaffecting to him as a problem in
Euclid.
21. Owing to the recognized dependence of peculiar instincts and modes
of reaction on peculiarities of structure, comparative anatomists
are quite confident, when they find a portion of a skull with two
occipital condyles, that the animal to which this skull belonged had
red blood-corpuscles without nuclei, and (if a female) suckled its
young. If in that fragment of skull there remain a single tooth, it
will prove that the animal was carnivorous or herbivorous, and had, or
had not, retractile claws. From such data a general conclusion may be
formed as to the instincts and habits of the animal. The data disclose
much of the primary constitution, that is to say, the mechanism
which the animal brought with it into the world, ready prepared to
react in definite ways on being stimulated. The connate mechanism
has correlative tendencies of reaction. Some of these tendencies are
inevitably called into play by external conditions, and they continue
unaltered amid great varieties of circumstances, provided none of these
variations directly deprive them of their appropriate stimulation.
Such tendencies of the connate mechanism are styled _automatic_ (an
unfortunate metaphor, which has led to the theory of Automatism), and
include, besides the visceral reactions, the more complex reactions
of winking, breathing, swallowing, coughing, flying, walking, etc. It
is true that we learn to walk, and learn to wink, whereas the other
actions require no tentative efforts directed by experience; but the
mechanism of all these actions is already laid down in the primary
constitution, and is inevitably called into play.
22. The instincts also belong to the connate mechanism, and in the
course of the normal experience of the animal inevitably come into
play; but, unlike the automatic tendencies of breathing, swallowing,
and coughing, they are capable of modification, or even suppression,
by alterations in the course of individual experience. The connate
mechanism of the cat determines its dread of water, and its enmity
to the dog and mouse; yet a cat will by the modifications of certain
experiences become as ready as an otter to take to the water, and
become so fond of a dog that she will allow him to tend upon her
kittens; and so indifferent to the mouse that she will let it run
over her body. All this implies a new adjustment in the nervous
centres, with new modes of reaction on sensory impressions: the
inherited mechanism has been modified. I need not dwell on the profound
modifications which the human inherited mechanism undergoes in the
course of experience--how social influences and moral and religious
teachings redirect, or even suppress, many primary tendencies; so that
“moral habits” become organized, and replace the original tendencies
of the organism. These, when organized, become the inevitable modes
of reaction, and are sometimes called secondarily automatic. It
is important to recognize this organization of experiences, this
acquisition of a secondary or modified constitution, if we would
explain psychological processes by physiological processes. Thus
the processes of Logic are automatic, they belong to the connate
primary mechanism, and their action is inevitable, invariable. The
elements of a judgment, like the elements of a perception, may vary,
and we therefore say that one judgment is false, and one perception
incomplete; but the judging process is always the same, and the
perceiving process is always the same. We may breathe pure air or
impure air, but the breathing process is in each case the same; and
judgment is as automatic as breathing, not to be altered, not to be
suppressed. Again, the moral terror at wickedness of any recognized
kind is as automatic as the instinctive terror at danger. The one has
its roots in the primary disposition called love of approbation and
its correlative dread of disapprobation: the social instinct. The
other has its root in the primary disposition called “instinct of
self-preservation,” which is really the reflex shrinking from pain: the
physiological instinct.
23. Besides the connate and acquired mechanism, we have now to consider
the temporary and fluctuating adjustments which represent the statical
condition of the organism at each moment. The automatism of the primary
constitution is such that previous experience and conscious effort
are not needed; nor will any experience or any effort alter the mode
of reaction. If a strong light falls on the eye, the iris contracts;
if the eyeball is dry, the eyelid drops; if sound-waves beat upon the
tympanum, the stapedius muscle contracts; if the lining of the throat
be tickled, the muscles involved in coughing or in vomiting contract.
No experience is necessary for these actions, some of which are so
complicated that if we had to learn them, as we learn far simpler
actions, the organism would perish before the power was attained. Yet
all of these presuppose a certain normal state of the mechanism, any
considerable variation in which will modify or suppress them.
24. Secondarily automatic actions are those which have been acquired
through experiences that have modified the organism, and produced a
new adjustment of parts. We learn to shield the eyes against a strong
glare of light by raising the hand; by winking we learn to shield the
eye against an approaching body; we also learn to turn the head in the
direction of a sound, and to thrust away with our hands the object that
is irritating our skin. Experience has been necessary for all these
actions, and has finally organized the tendencies to perform them,
so that the reaction is invariable, inevitable, unless controlled by
the will. If you tickle my throat, I may, or may not, push aside your
hand; but if the inside of my throat be tickled, I must cough. Here
we see the difference between the automatic and secondarily automatic
actions. The second being due to individual experience, are more or
less controllable; and whether they are or are not controlled depends
on the condition of the nerve-centres at the moment. You may tickle my
throat, or irritate my skin, without causing any movement of my hands
to thwart you, either because my nerve-centres are preoccupied by other
stimulations, and I am not conscious of the irritation, or because I do
not choose to thwart you.
25. It should be added that some secondarily automatic actions have
become so firmly organized that we can only with great difficulty
interfere with them. Others never enter into consciousness, and are
therefore often supposed to be purely mechanical. The movement of the
eye towards the brightest light, and the convergence of the axes of
both eyes, are reflexes which, although involuntary and unconscious,
are the products of education. They do not belong to the connate
constitution, although they are so inevitably acquired by experience
that they belong to every normal child. At first the infant stares with
a blank gaze, and its eyes, though moving under the stimulus of light,
move incoherently; the axes never converge except by accident. Very
early, however, the infant’s eyes are observed to follow the movements
of a bright light; and at last they acquire so certain and rapid a
power of adjustment that the eyes shift from spot to spot, always
“fixing” the object by bringing the most sensitive part of the retina
to bear on it. The incoherent movements have become precisely regulated
movements. It is the same with speech. The vocal organs are exercised
in an incoherent babble. By degrees these movements become regulated
so as to respond definitely to definite stimuli, and words are formed,
then sentences, till finally fluent speech becomes in a great degree
automatic. The vocal muscles respond to an auditory stimulus, and the
child repeats the word it has heard, just as the eye-muscles respond
to a retinal stimulus. That we acquire the power of converging the
axes, and accommodating the lens to near objects, is not only proved by
observation of infants, but also by cases of disease. After the reflex
mechanism has been long established, so that it acts with inevitable
precision, a slight paralysis of one of the muscles has the effect of
making all objects appear in a different position; the patient trying
to touch an object, then always moves his hand on one side of it. Von
Graefe relates the case of a stonebreaker who always struck his hand
with the hammer when he tried to strike the stone. Yet this very man
_learned_ to accommodate his movements to the new impressions; so that
if his paralysis had been cured, his modified mechanism would have been
ill adapted to the new conditions, and he would once more have struck
his hand instead of the stone.
26. This digression on the native and acquired dispositions of the
organism, while it has brought into strong light all that can be cited
in favor of regarding animal bodies as mechanisms, and their actions
as the direct consequences of mechanical adjustments, has also made
conspicuous the radical difference between an organism and a machine.
We cannot too emphatically insist on this radical difference. Between
the group of conditions involved in the structure and action of a
machine, and the group of conditions involved in the structure and
action of an organism, there are contrasts as broad as any that can be
named. To overlook these in taking account solely of the conditions
common to both groups is a serious error. On such grounds we might
insist that a tiger is a violet, because both are organisms.
The biologist will admit that an organism is a mechanism, and (in
so far as its bodily structure is concerned) a material mechanism.
All the actions of this structure are therefore mechanical, in the
two senses of the term: first, as being the actions of material
adjustments; secondly, as being movements, and thereby included under
the general laws of motion represented in Mechanics; the abstract
laws of movement for an organic body are not different from the
abstract laws of movement for an inorganic body. So far we have been
considering the abstract relations only. No sooner do we consider the
phenomena as concrete wholes, than we find great diversity in the modes
of production of the movements in organisms and machines. Now it is
precisely the modes of production which have interest for us. We never
understand a phenomenon so as to gain any practical control over it, or
any theoretical illumination from it, unless we have mastered some of
its conditions; our knowledge of these conditions is the measure of our
power.
CHAPTER III.
THE RELATION OF BODY AND MIND.
27. The second question proposed was, In what sense can Feeling be
correctly spoken of as an Agent in organic processes? This brings
us face to face with a much-debated topic, the relation of Body and
Mind; and demands a theoretic interpretation of that First Notion
which expresses universal experience, namely, that what I know as
Myself is a Body, in one aspect, and a Soul, in the other. What I
call my Body is a persistent aggregate of objective phenomena; and
my Soul is a persistent aggregate of subjective phenomena: the one
is an individualized group of experiences expressible in terms of
Matter and Motion, and therefore designated _physical_; the other an
individualized group of experiences expressible in terms of Feeling,
and therefore designated _psychical_. But, however contrasted, they
are both simply embodiments of Experience, that is to say, are Modes
of Feeling. All Existence--as known to us--is the Felt. The laws of
our organism compel us, indeed, to postulate an Existent which is
_extra mentem_--a Real not Ourselves--but the same laws debar us from
any knowledge whatever of what this _is_, or is _like_. We know Things
absolutely _in so far_ as they exist in relation to us; and that is the
only knowledge which can have any possible significance for us.
28. It is impossible for me to doubt that I am a Body, though I may
doubt whether what is thus called is anything more than a group of
feelings. It is impossible for me to doubt that I am a Soul; though
I may doubt whether what is thus called is more than a group of
bodily functions. In separating what is unquestionable from what is
questionable, we separate the fundamental facts of consciousness
from the theoretic interpretations of those facts: no theoretic
interpretation can efface or alter the facts. Whatever Philosophy may
discover, it cannot displace the fact that I know I am a Soul, _in
every sense in which that phrase represents Experience_: I know the
Soul in knowing its concretes (feelings), and in knowing it as an
abstraction which condenses those concretes in a symbol. The secondary
question is, Whether this abstraction represents one Existent, and the
abstraction Body another and wholly different Existent, or the two
abstractions represent only two different Aspects? this may be debated,
and must be answered according to theoretic probabilities.
29. What are the probabilities? We are all agreed that Consciousness
is the final arbiter. Its primary deliverance is simply that
of _a_ radical distinction. It is silent on the nature of the
distinction--says nothing as to whether the distinction is one of
agents or of aspects. It says, “I am a Soul.” With equal clearness
it says, “I am a Body.” It does _not_ say, “I am two things.” Nor
does the fact of a radical distinction imply more than a contrast of
aspects, such as that of convex and concave. The curve has at every
point this contrast of convex and concave, and yet is the identical
line throughout. A mental process is at every point contrasted with
the physical process assumed to be its correlate; and this contrast
demands equivalent expression in the terms of each. The identity
underlying the two aspects of the curve is evident to Sense. The
identity underlying the mental and physical process is not evident to
Sense, but may be made eminently _probable_ to Speculation, especially
when we have explained the grounds of the difference, namely, that they
are apprehended through different modes. But although I admit that
the conclusion is only one of probability, it is one which greatly
transcends the probability of any counter-hypothesis. Let us see how
this can be made out.[208]
30. We start from the position that a broad line of demarcation must
be drawn between the mental and the physical aspect of a process,
supposing them to be identical in reality. Nothing can be more _unlike_
a logical proposition than the physical process which is its correlate;
so that Philosophy has hitherto been forced to forego every attempt at
an explanation of how the two can be causally connected: referring the
connection to a mystery, or invoking two different agents, spiritual
and material, moving on parallel lines, like two clocks regulated to
work simultaneously. But having recognized this difference, can we not
also discern fundamental resemblances? First and foremost, we note
that there is common to both the basis in Feeling: they are both modes
of Consciousness. The Mind thinking the logical proposition is not,
indeed, in the same _state_ as the Mind picturing the physical process
which is the correlate of that logical proposition--no more than I,
who see you move on being struck, have the same feelings as you who
are struck. But the Mind which pictures the logical proposition as
a process, and pictures the physical process as a bodily change, is
contemplating one and the same event under its subjective and objective
aspects; just as when I picture to myself the feelings you experience
on being struck I separate the subjective aspect of the blow from its
objective aspect. Secondly, between the logical proposition and the
physical process there is a community of causal dependence, i. e. the
mode of grouping of the constituent elements, whereby this proposition,
and not another, is the result of this grouping, and not another. In
fact, what in subjective terms is called Logic, in objective terms is
Grouping.
31. Let us approach the question on a more accessible side. Sensation
avowedly lies at the basis of mental manifestations. Now, rightly
or wrongly, Sensation is viewed alternately as a purely subjective
fact--a psychological process--and as a purely objective fact--the
physiological reaction of a sense-organ. It is so conspicuously a
physiological process that many writers exclude it from the domain
of Mind, assign it to the material organism, and believe that it is
explicable on purely mechanical principles. This seems to me eminently
disputable; but the point is noticed in proof of the well-marked
objective character which the phenomenon assumes. In this aspect a
sensation is simply the reaction of a bodily organ. The physiologist
describes how a stimulus excites the organ, and declares its reaction
to be the sensation. Thus viewed, and expressed in terms of Matter
and Motion, there is absolutely nothing of that subjective quality
which characterizes sensation. Yet without this quality the objective
process cannot be a sensation. Exclude Feeling, and the excitation of
the auditory organ will no more yield the sensation of Sound by its
reaction, than the strings and sounding-board of a piano when the keys
are struck will yield music to a deaf spectator. Hence the natural
inference has been that inside the organism there is a _listener_: the
Soul is said to listen, transforming excitation into sensation. This
inference only needs a more systematic interpretation and it will
represent the biological theory, which demands something _more_ than
the reaction of the sensory organ--namely, the reaction of the whole
organism _through_ the sensory organ. I mean, that no organ isolated
from the organism is capable of a _physiological_ reaction--only
of a physico-chemical reaction; and sensation depends on (_is_)
the physiological reaction. When a sense-organ is stimulated, this
stimulation is a vital process, and is raised out of the class of
physico-chemical processes by virtue of its being the indissoluble
part of a complex whole. Interfere with any one of the co-operant
conditions--withdraw the circulation, check respiration, disturb
secretion--and the sense-organ sinks from the physiological to the
physical state; it may then be brought into contact with its normal
stimuli, but no stimulation (in the vital sense) will take place, there
will be no vital reaction.
Condensing all vital processes in the symbol Vitality, we may say
Vitality is requisite for every physiological process. A parallelism
may be noted on the subjective side: all the sentient processes may be
condensed in the one symbol Sensibility (Feeling), and we must then
say, No psychological process is possible as an isolated fact, but
demands the co-operation of others--it is a _resultant_ of all the
contemporaneous conditions of Sensibility in the organism. In ordinary
language this is what is meant by saying that no impression can become
a sensation without the intervention of Consciousness--an ambiguous
phrase, because of the ambiguity of the term Consciousness, but the
phrase expresses the fact that in Sensation a process in the organism
is necessary to the reaction of the organ.
32. Having recognized the distinction between the two processes
objective and subjective, physical and mental, we have recognized
the vanity of attempting to assign their limits, and to say where
Motion ends and Feeling begins, or how Feeling again changes into
Motion. The one does _not_ begin where the other ends. According to the
two-clock theory of Dualism, the two _agents_ move on parallel lines.
On the theory of Monism the two _aspects_ are throughout opposed. Both
theories explain the facts; which explanation is the most congruous
with experience? Against the first we may object that the hypothesis of
two Agents utterly unallied in nature wants the cardinal character of
a fertile hypothesis in its unverifiableness: it may be true, we can
never know that it is true. By the very terms of its definition, the
Spirit--if that mean _more_ than an abstract expression of sentient
states--is beyond all sensible experience. This is indeed admitted by
the dualists, for they postulate a Spirit merely because they cannot
otherwise explain the phenomena of Consciousness. Herein they fail to
see that even their postulate brings no explanation, it merely restates
the old problem in other terms.
33. Up to the present time these same objections might have been urged
with equal force against Monism. Indeed, although many philosophers
have rejected the two-clock theory of Leibnitz, they have gained a very
hesitating acceptance for their own hypothesis of identity. To most
minds the difficulty of imagining how a physical process could _also_
be a psychical process, a movement also be a feeling, seemed not less
than that of imagining how two such distinct Agents as Matter and Mind
could co-operate, and react on each other, or move simultaneously on
parallel lines. Although for many years I have accepted the hypothesis
of Monism, I have always recognized its want of an adequate reply to
such objections. Unless I greatly deceive myself, I have now found
a solution of the main difficulty; and found it in psychological
conditions which are perfectly intelligible. But knowing how easily one
may deceive one’s self in such matters, I will only ask the reader to
meditate with open-mindedness the considerations now to be laid before
him, and see if he can feel the same confidence in their validity.
34. One of the early stages in the development of Experience is the
separation of Self from the Not-Self. I look out on “the vast extern
of things,” and see a great variety of objects, included in a visible
hemisphere. All these objects in various positions, having various
forms and colors, I believe to be wholly detached from, and in every
way unallied to, Myself. And what is that Self? It is my Body as a
visible and tangible object, separated from all other visible and
tangible objects by the constant presence of feelings connected with
it and its movements, and not connected with the other objects. This
constant presence of feelings is referred to a Soul, which I then
separate from my Body, as an Inner Self; and from this time onwards I
speak of the Body as _mine_, and learn to regard it in much the same
light as other outer objects. In my naïve judgment the external objects
are supposed to exist _as_ I see and touch them, whether I or any one
else see and touch them or not: they in no sense belong to the series
of feelings which constitute the Me. And since my Body resembles these
objects in visible and tangible qualities, and also in being external
to my feelings, it also takes its place in the objective world. Thus
arises the hypothesis of Dualism which postulates a _Physis_, or
object-world, and an _Æsthesis_, or subject-world: two independent
existents, one contemplated, the other contemplating.
35. Philosophy, as we know, leads to a complete reversal of this
primitive conclusion, and shows that the _contemplated_ is a _synthesis
of contemplations_, the Physis being _also_ the Æsthesis. Psychological
investigation shows that the objects supposed to _have_ forms,
colors, and positions within an external hemisphere, have these
only in virtue of the very feelings from which they are supposed
to be separated. The _visible_ universe exists only _as seen_: the
objects are Reals conditioned by the laws of Sensibility. The space
in which we see them, their geometrical relations, the light and
shadows which reveal them, the forms they affect, the lines of their
changing directions, the qualities which distinguish them,--all these
are but the externally projected signs of feelings. They are signs
which we interpret according to organized laws of experience; each
sign being itself a feeling connected with other feelings. We project
them outside according to the “law of eccentric projection”--which is
only the expression of the fact that one feeling is a sign of some
other, and is thereby _ideally detached_ from it. According to this
law I say, “my Body”; just as I say, “my House”; or, “my Property.”
Misled by this, Dualism holds that in the very fact of detaching my
Body from my Self, calling it _mine_, is the revelation of a distinct
entity within the body. But that this is illusory, appears in the
application of this same law of eccentric projection to sensations
and thoughts, which are called _mine_, as my legs and arms are mine.
If it is undeniable that I say _my_ Body--and thus ideally detach the
Body from the Soul--it is equally undeniable that I say _my_ Soul; and
from what is the Soul detached? In presence of this difficulty, the
metaphysician may argue that neither Body nor Soul can be coextensive
with its manifestations, but demands a noumenal Real for each--a
_substratum_ for the bodily manifestations, and a _substratum_ for the
mental manifestations. This, however, is an evasion, not a solution of
the difficulty. If we postulate an unknown and unknowable noumenon,
we gain no insight: first, because Philosophy deals only with the
known functions of unknown quantities, and therefore leaves the _x_
out of the calculation; secondly, because, granting the existence of
these noumena, we can have no rational grounds for asserting that they
are not of one and the same nature; for we have no grounds for _any_
assertion whatever about them. And if it be urged against this, that
Consciousness testifies to a distinction, I answer that on a closer
scrutiny it will be found to testify to nothing more than a diversity
of manifestation. All therefore that comes within the range of
knowledge is, How does this diversity arise?
36. There are two ways, and there are only two, in which differences
arise. These are, 1°, the _modes of production_ of a product, and,
2°, our _modes of apprehension_ of the product. Things may be very
different, and yet to our apprehension indistinguishable, so that
we regard them as identical; and they may be identical, yet appear
utterly unlike. A mechanical bird may seem so like a living bird, and
their actions so indistinguishable to the spectator, that he will not
suspect a difference, or suspecting it, will not be able to specify
it. Of both objects, so long as his modes of apprehending them are
circumscribed, he can only say what these imply: he sees familiar
forms, colors, and movements, which he interprets according to the
previous experiences of which these are the signs. But by varying the
modes of apprehension, and gaining thus a fuller knowledge, he finds
that the two products have very different modes of production; hence he
concludes the products to be different: the mechanism of the one is not
the organism of the other; the actions of the mechanical bird are not
the actions of the living bird. The fuller knowledge has been gained
by viewing the objects under different relations, and contemplating
them _in_ their modes of production, not as merely visible products. He
sees the mechanism performing by steel springs, wheels, and wires, the
work which the organism performs by bones, muscles, and nerves; and the
farther his analysis of the modes of production is carried, the greater
are the differences which he apprehends.
37. Now consider the other side. One and the same object will
necessarily present very different aspects under different subjective
conditions, since it is _these_ which determine the aspect. The object
cannot be to Sight what it is to Hearing, to Touch what it is to
Smell. The vibrations of a tuning-fork are seen as movements, heard
as sounds. In current language the vibrations are said to cause the
sounds. Misled by this, philosophers puzzle themselves as to how a
material process (vibration) can be transformed into a mental process
(sensation), how such a cause can have so utterly different an effect.
But I have formerly[209] argued at some length that there is no
transformation or causation of the kind supposed. The tuning-fork--or
that Real which in relation to Sense is the particular object thus
named--will, by one of its modes of acting on my Sensibility through
my optical apparatus, determine the response known as _vibrations_;
but it is not this response of the optical organ which is transformed
into, or causes the response of the auditory organ, known as _sound_.
The auditory organ knows nothing of vibrations, the optical nothing of
sounds. The responses are both modes of Feeling determined by organic
conditions, and represent the two different relations in which the
Real is apprehended. The Real _is_ alternately the one and the other.
And if the one mode of Feeling has a physical significance, while the
other has a mental significance, so that we regard the vibrations as
objective facts, belonging to the external world, and the sounds as
subjective facts, exclusively belonging to the internal world, this is
due to certain psychological influences presently to be expounded.
Meanwhile let us fix clearly in our minds that both vibrations and
sounds are modes of Feeling. My consciousness plainly assures me
that it is I who see the one, and hear the other; not that there are
two distinct subjects for the two distinct feelings. Add to which,
manifold uncontradicted experiences assure me that the occasional
cause--the objective factor--of the one feeling, is also the cause of
the other, and not that the two feelings have two different occasional
causes. From both of these undeniable facts we must conclude that the
difference felt is simply a difference of aspect, determined by some
difference in the modes of apprehension.
38. Assuming then that a mental process is only another aspect
of a physical process--and this we shall find the more probable
hypothesis--we have to explain by what influences these diametrically
opposite aspects are determined. From all that has just been said we
must seek these in the modes of apprehension. There can be no doubt
that we express the fact in very different terms; the question is,
What do these terms _signify_? Why do we express one aspect in terms
of Matter and Motion, assigning the process to the objective world;
and the other aspect in terms of Feeling, assigning the process to the
subjective world?
Let the example chosen be a logical process as the mental aspect,
and a neural process as its physical correlate. The particular
proposition may be viewed logically, as a grouping of experiences,
or physiologically, as a grouping of neural tremors. Here we have
the twofold aspect of one and the same reality; and these different
aspects are expressed in different terms. We cannot be too rigorous
in our separation of the terms; for every attentive student must have
noted how frequently discussions are made turbid by the unconscious
_shifting of terms_ in the course of the argumentation. This is not
only the mistake of opponents who are unaware of the shifting which has
occurred in each other’s minds, so that practically the adversaries
do not meet on common ground, but cross and recross each other; it is
also the mistake of the solitary thinker losing himself in the maze
of interlacing conceptions instead of keeping steadily to one path.
Only by such shifting of terms can the notion of the physical process
causing, or being transformed into, the mental process for a moment
gain credit; and this also greatly sustains the hypothesis of Dualism,
with its formidable objections: How can Matter think? How can Mind act
on Matter causing Motion?
39. Those who recognized that the terms Matter and Mind were
abstractions mutually exclusive, saw at once that these questions,
instead of being formidable, were in truth irrational. To ask if
Matter could think, or Mind move Matter, was a confusion of symbols
equivalent to speaking of a yard of Hope, and a ton of Terror. Although
Measure and Weight are symbols of Feeling, and in _this_ respect are
on a par with Hope and Terror, yet because they are objective symbols
they cannot be applied to subjective states, without violation of the
very significance they were invented to express. No one ever asks
whether a sensation of Sound can be a sensation of Color; nor whether
Color can move a machine, although Heat can, yet the one is no less a
sensation than the other. On similar grounds no one should ask whether
Matter can think, or Mind move Matter. The only rational question is
one preserving the integrity of the terms, namely, whether the living,
thinking organism presents itself to apprehension under the twofold
aspect--now under the modes of Feeling classified as objective or
physical; now under the modes classified as subjective or mental.
40. We are told that it is “impossible to imagine Matter thinking,”
which is very true; only by a gross _confusion_ of terms can Thought
be called a property of cerebral tissue, or of Matter at all. We
may, indeed, penetrate beneath the terms which relate to aspects,
and recognize in the underlying reality not two existences, but one.
Our conceptions of this reality, however, are expressed in symbols
representing different classes of feelings, objective and subjective;
and to employ the terms of one class to designate the conceptions of
the other is to frustrate the very purposes of language. Matter and
Mind, Object and Subject, are abstractions from sentient experiences.
We know them as abstractions, and know the concrete experiences from
which they are abstracted. Philosophers, indeed, repeatedly assure us
that we neither know what Matter is nor what Mind is, we only know the
_phenomenal products_ of the action and reaction of these two unknown
noumena. Were this so, all discussion would be idle; we could not say
whether Matter was or was not capable of thinking, whether Mind was or
was not the same as Matter, we could only abstain from saying anything
whatever on the topic. What should we reply to one who asked us to
name the product of two unknown quantities? So long as _x_ and _y_ are
without values their product must be without value. If the value of
_x_ be known, and that of _y_ unknown, then the product still remains
unknown: _x_ + _y_ = _x_ + 0 = _x_. Therefore, unless the Objective
aspect were the _equivalent_ of the Subjective aspect, it could never
be subjectively present. Feeling is but another aspect of the Felt.
41. It is because we do know what Matter is, that we know it is
_not_ Mind: they are symbols of two different modes of Feeling. If
we separate the conception of citizenship from the conception of
fatherhood, although the same man is both citizen and father, how much
more decisively must we separate the conception of Matter, which
represents one group of feelings, from the conception of Mind, which
represents another? One element in the former is common to the whole
group, namely, the reference to a Not-Self, induced by the sensation of
Resistance, which always ideally or sensibly accompanies the material
class. The axiom, I feel, _ergo_ I exist, has its correlative:--I act,
_ergo_ there are other existents on which I act; and these are not
wholly Me, for they resist, oppose, exclude me; yet they are also one
with Me, since they are felt by me. In my Feeling, that which is not Me
is Matter, the objective aspect of the Felt, as Mind is the subjective
aspect.
But since Hunger and Thirst, Joy and Grief, Pain and Terror, are also
_felt_, yet are never classed under the head of Matter, the grounds of
the classification of feelings have to be expressed. Professor Bain
makes the distinction between Matter and Mind to rest solely on the
presence or absence of Extension: this is the decisive mark: Matter
he defines as the Extended. The definition is inadequate. When I see
a dog and its image reflected in a pool, or see a dog and think of
another, in the three cases dog, image, and idea have Extension; but
I recognize the dog as a material fact, the idea as a mental fact;
and although the image of the dog has material conditions by which
I am optically affected, just as the idea has material cerebral
conditions, I recognize a marked difference between them and the dog,
due to the different modes of apprehension. The dog is known as a
persistent reality, which, when Sight is supplemented by Touch, will
yield sensations of Resistance, and thus disclose its materiality. The
image vanishes if I attempt to touch it; I see its outlines waver and
become confused with every disturbance of the surface of the pool;
the idea vanishes when another idea arises; whence I conclude that
neither has material reality, because neither has the Resistance which
characterizes the Not-Self. The image and the idea may be referred to
material conditions, but so may pains, terrors, volitions, yet these
are all without Extension, simply because they are not visual feelings.
42. Matter does not represent all feelings, but only the objective
sensibles; and these are not all characterized by Extension, but only
those which directly or indirectly involve optico-tactical experiences
accompanied by muscular experiences. Matter is primarily the Visible
and Resistant; and secondarily, whatever can be imagined as such;
so that ether, molecules, and atoms, although neither visible nor
tangible, are ranged under the head of Matter. Color is a feeling as
Sound and Scent are feelings, and although material conditions are
equally presupposed in all three, yet Color alone has Extension, and
because it can be imaged it has a more objective character than the
others, which having no lines and surfaces, want the optical conditions
for the formation of images, and are less definitely connected with
tactical and muscular experiences. Nevertheless, since Sound and Scent
are obviously associated with objects seen and touched, they have a
degree of materiality never assigned to such feelings as Hunger and
Thirst, Pleasure, Terror, and Hope.
43. When we refer feelings to material conditions, we follow the
natural tendency to translate the little known in terms of the better
known, and employ the symbols Matter and Motion, because these furnish
the intellect with images, i. e. definite and exact elements to operate
with. In hearing a sound, there is nothing at all like “vibrations,”
nothing like “aerial waves” and “neural processes,” given in that
feeling; but on attempting to _explain_ it, we remove it from the
sphere of Sensation to carry it into the sphere of Intellect, and
we must change our symbols in changing our problem; here our only
resource is to translate the subjective state into an _imaginable_
objective process, which can only be expressed in terms of Matter
and Motion. What we _heard_ as Sound is then _seen_ as Vibration.
When we are optically or mentally contemplating vibrations and neural
processes, we are supplanting one source of feeling by another,
translating an event in another set of symbols. But we can no more hear
the sound in seeing the vibrations, than a blind man can see the fly
in the amber which he feels with his fingers, or than we can feel the
amber he holds, while we are only looking at it. The phrase “material
conditions of Feeling” sometimes designates the objective aspect of the
subjective process, and sometimes the agencies in the external medium
which co-operate with the organism in the production of the feelings.
In each case there is an attempt to explain a feeling by intelligible
symbols.
44. The Animal probably never attempts such explanation; satisfied with
the facts, it is careless of their factors. Man is never satisfied:
is restless in the search after factors; and having found them, seeks
factors of these factors; so that Lichtenberg felicitously calls him
“_das rastlose Ursachenthier_”--“the animal untiring in the search
for causes.” And thus sciences arise: we translate experiences into
geometrical, physical, chemical, physiological, and psychological
terms--different symbols of the different modes of apprehending
phenomena.
45. “I see an elephant.” In other words, I am affected in a certain
way, and interpret my affection by previous similar experiences,
expressing these in verbal symbols. But I want an explanation, and
this the philosopher vouchsafes to me by translating my affection into
his terms. He takes me into another sphere--tells me of an undulating
Ether, the waves of which beat upon my retina--of lines of Light
refracted by media and converged by lenses according to geometric
laws--of the formation thereby of a tiny image of the gigantic elephant
on my retina as on the plate of a camera-obscura--this, and much
more, is what _he_ sees in _my_ visual feeling, and he bids me see it
also. Grateful for the novel instruction, I am compelled to say that
it does not alter my vision of the elephant, does not make the fact
a whit clearer, does not indeed correspond with what I feel. It is
outside knowledge, valuable, as all knowledge is, but supplementary.
It is translation into another language. And when I come to examine
the translation, I find it very imperfect. I ask my instructor: Is
it the tiny image on my retina which I see, and not the big elephant
on the grass? And how do I see this retinal image, which you explain
to be upside down?--how is it carried from my retina to my mind? I
have no consciousness of tiny reversed image, none of my retina,
only of a fact of feeling, which I call “seeing an elephant.” The
camera-obscura has no such feeling--it reflects the image, it does
not see the object. Here my instructor, having reached the limit
of his science,[210] hands me over to the physiologist, who will
translate the fact for me in terms not of Geometry, but of Anatomy
and Physiology. The laws of Dioptrics cease at this point: the image
they help to form on the retina is ruthlessly dispersed, and all its
beautiful geometric construction is lost in a neural excitation, which
is transmitted through semifluid channels of an optic tract to a
semifluid ganglion, whence a thrill is shot through the whole brain,
and is there _transformed_ into a visual sensation. Again I fancy I
have gained novel instruction of a valuable kind; but it does not
affect my original experience that I am enabled to translate it into
different terms; the less so because I cannot help the conviction that
the translation is imperfect, leaving out the essential points. If a
phrase be translated for me into French or German, I gain thereby an
addition to my linguistic knowledge, but the experience thus variously
expressed remains unaffected. When the fact is expressed in geometrical
or physiological terms, the _psychical process_ finds no adequate
expression. Neither in the details, nor in the totals, do I recognize
any of the qualities of my state of feeling in seeing the elephant.
I do not see the geometrical process, I do not see the anatomical
mechanism, I see the elephant, and am conscious only of that feeling.
You may consider my organism geometrically or anatomically, and bring
it thus within the circle of objective knowledge; but my subjective
experience, my spiritual existence, that of which I am most deeply
assured, demands another expression. Nay more, on closely scrutinizing
your objective explanations, it is evident that a psychical process
is _implied_ throughout--such terms as undulations, refractions,
media, lenses, retina, neural excitation, overtly refer, indeed, to
the material objective aspect of the facts, but they are themselves
the modes of Feeling by which the facts are apprehended, and would not
exist _as such_ without the “greeting of the spirit.”
46. What, then, is our conclusion? It is, that to make an adequate
explanation of psychical processes by material conditions we must first
establish an equivalence between the subjective and objective aspects;
and, having taken this step, we must complete it by showing wherein the
difference exists; having established this entity and diversity, we
have solved the problem.
Let us attempt this solution. When I speak to you, the spoken words
are the same to you and to me. You hear what I hear, you apprehend
what I apprehend. But there were muscular movements of articulation
felt by me and not felt by you; to feel these you also must articulate
the words; but so long as you merely hear the words, there is a
difference in our states of feeling. Some of my movements you can see,
others you can imagine; but this is not my feeling of them, it is your
optical equivalent of my muscular feeling. On a similar assumption of
equivalence, a neural process is made to stand for a logical process.
In thinking a proposition, we are logically grouping verbal symbols
representative of sensible experiences; and this is a quite peculiar
state of Consciousness, wholly unlike what would arise in the mental or
visual contemplation of the neural grouping, which is its physiological
equivalent. But this diversity does not discredit the idea of their
identity; and although some of my readers will protest against such an
idea, and will affirm that the logical process is not a process taking
place in the organism at all, but in a spirit which uses the organism
as its instrument, I must be allowed in this exposition to consider
the identity established, my purpose being to explain the diversity
necessarily accompanying it. Therefore, I say, that although a logical
process is identical with a neural process, it must appear differently
when the modes of apprehending it are different. While you are thinking
a logical proposition, grouping your verbal symbols, I, who mentally
_see_ the process, am grouping a totally different set of symbols: to
you the proposition is a subjective state, i. e. a _state_ of feeling,
not an _object_ of feeling: to become an object, it must be apprehended
by objective modes: and this it can become to you as to me, when we see
it as a process, or imagine it as a process. But obviously your state
in seeing or imagining the process must be different from your state
when the process itself is passing, since the modes of apprehension
are so different. There may be every ground for concluding that a
logical process has its correlative physical process, and that the two
processes are merely two aspects of one event; but because we cannot
apprehend the one aspect as we apprehend the other, cannot _see_ the
logical sequence as we _see_ the physical sequence, this difference in
our modes of apprehension compels us to separate the two, assigning
one to the subjective, the other to the objective class. Between the
sensible perception of an object and the reproduced image of the object
there is chiefly a quantitative difference in the physiological and
psychological processes: the image is a faint sensation. Yet this
quantitative difference brings with it the qualitative distinction
which is indicated in our calling the one a sensation, the other a
thought. The consequence has been that while all philosophers have
admitted the sensation to be--at least partly--a process in the bodily
organism, the majority have maintained that the thought is no such
process in the organism, but has its seat in a spirit independent of
the organism.
47. The states of Feeling which are associated with other states
characterized as objective because overtly referring to a Not-Self, we
group under the head of Matter: we assign material conditions as their
antecedents. Whereas states of Feeling which are not thus associated we
group under the head of Mind, and assign internal conditions as their
antecedents. Color and Taste are very different states of Feeling, yet
both are spontaneously referred to external causes, because they are
associated with visual and tactical states; whereas Hunger, Nausea,
Hope, etc., have no such associations, and their material conditions
are only theoretically assigned.
Our intelligible universe is constructed out of the elements of Feeling
according to certain classifications, the broadest of which is that
into external and internal, object and subject. The abstractions Matter
and Mind once formed and fixed in representative symbols, are easily
accredited as two different Reels. But the separation is ideal, and
is really a distinction of Aspects. We know ourselves as Body-Mind;
we do not know ourselves as Body _and_ Mind, if by that be meant two
coexistent independent Existents; and the illusion by which the two
Aspects appear as two Reals may be made intelligible by the analysis
of any ordinary proposition. For example, when we say “this fruit
is sweet,” we express facts of Feeling--actual or anticipated--in
abstract terms. The concrete facts are these: a colored feeling, a
solid feeling, a sweet feeling, etc., have been associated together,
and the colored, solid, sweet group is symbolized in the abstract
term “fruit” But the color, solidity, and sweetness are also abstract
terms, representing feelings associated in other groups, so that we
find “fruit” which has no “sweetness”; and “sweetness” in other things
besides “fruits.” Having thus separated ideally the “sweetness” from
the “fruit”--which in the concrete sweet-fruit is not permissible--we
easily come to imagine a real distinction. This is the case with the
concrete living organism when we cease to consider it in its concrete
reality, and fix our attention on its abstract terms--Body and Mind. We
then think of Body apart from Mind, and believe in them as two Reals,
though neither exists apart.
There is no state of consciousness in which object and subject are
not indissolubly combined. There is no physical process which is
not indissolubly bound up with the psychical modes of apprehending
it. Every idea is either an image or a symbol--it has therefore
objective reference, a material aspect. Every object is a synthesis
of feelings--it has therefore subjective reference, a material
aspect. Thus while all the evidence points to the identity of Object
and Subject, there is ample evidence for the logical necessity of
their ideal separation as Aspects. This I have explained as a case
of the general principle which determines all distinctions--namely,
the diversity in the modes of production of the products,
which--subjectively--is diversity in the modes of apprehending them.
The optico-tactical experiences are markedly different from the other
experiences, as being more directly referred to the Not-Self which
resists; and because these lend themselves to ideal constructions by
means of images and symbols, it is these experiences into which we
translate all the others when we come to explain them and assign their
conditions. For--and this is the central position of our argument--all
interpretation consists in translating one set of feelings in the terms
of another set. We condense sets of feelings in abstract symbols; to
_understand_ these we must reduce them to their concrete significates.
They are signs; we must show what they are signs of.
Now the symbols Object and Subject are the most abstract we can employ.
Because they are universal, they represent what cannot in reality be
divorced. We can, indeed, ideally separate ourselves from the Cosmos;
in the same way we can ideally separate our inner Self or Soul from our
outer Self or Body; and again our Soul from its sentient states, our
Body from its physical changes. But not so in reality. The separation
is a logical artifice, and a logical necessity for Science.
The necessity will be obvious to any one who reflects how the ideal
constructions of Science demand precision and integrity of terms. The
problem of Automatism brings this very clearly into view. The question
is, Can we translate all psychological phenomena in mechanical terms?
If we _can_, we ought; because these terms have the immense advantage
of being _exact_, dealing as they do with quantitative relations. But
my belief is that we cannot--nay, that we cannot even translate them
all into physiological terms. The distinction between quantitative and
qualitative knowledge (p. 354) is a barrier against the mechanical
interpretation. Physiology is a classificatory science, not a science
of measurement. Nor can the laws of Mind be deduced from physiological
processes, unless supplemented by and interpreted by psychical
conditions individual and social.
CHAPTER IV.
CONSCIOUSNESS AND UNCONSCIOUSNESS.[211]
48. Science demands precision of terms; and in this sense Condillac
was justified in defining it, “_une langue bien faite_.” The sciences
of Measurement are exact because of the precision of their terms, and
are powerful because of their exactness. The sciences of Classification
cannot aspire to this precision, and therefore, although capable of
attaining to a fuller knowledge of phenomena than can be reached
by their rivals, this advantage of a wider range is accompanied by
the disadvantage of a less perfect exposition of results. While
physicists and chemists have only to settle the significance of the
facts observed, biologists and social theorists have over and above
this to settle the significance of the terms they employ in expressing
the facts observed. Hence more than half their disputes are at bottom
verbal.
This is markedly the case in the question of Automatism. One man
declares that animals are automata; another that they are conscious
automata; and while it is quite possible to hold these views and not
practically be in disagreement with the views of ordinary men, or
indeed with the views of spiritualist and materialist philosophers,
we can never be sure that the advocates of Automatism do not mean
what they are generally understood to mean. If a man says that by an
automaton he does not here mean a machine, such as a steam-engine or
a watch, but a vital mechanism which has its parts so adjusted that
its actions resemble those of a machine; and if he adds that this
automaton is also conscious of some of its actions, though unconscious
of others, we can only object to his using terms which have misleading
connotations. If he mean by “conscious automata,” that animals are
mechanisms moved on “purely mechanical principles,” their consciousness
having nothing whatever to do with the production of their actions,
then indeed our objection is not only to his use of terms, but to his
interpretation of the facts.
49. The questions of fact are two: Are animal mechanisms rightfully
classed beside machines? and, Is consciousness a coefficient in the
actions of animal mechanism? The first has already been answered; the
second demands a preliminary settlement of the terms “conscious,”
“unconscious,” “voluntary,” and “involuntary.” The aim of Physiology
is to ascertain the particular combinations of the elementary parts
involved in each particular function--in a word, the mechanism of
organic phenomena; and the modern Reflex Theory is an attempt to
explain this mechanism on purely mechanical principles, without the
co-operation of other principles, especially those of Sensation and
Volition. It is greatly aided by the ambiguity of current terms. We are
accustomed to speak of certain actions as being performed unconsciously
or involuntarily. We are also accustomed to say that Consciousness
is necessary to transform an impression into a sensation, and that
Volition is the equivalent of conscious effort. When, therefore,
unconscious and involuntary actions are recorded, they seem to be
actions of an insentient mechanism. The Reflex Theory once admitted, a
rigorous logic could not fail to extend it to all animal actions.
50. I reject the Reflex Theory, on grounds hereafter to be urged,
but at present call attention to the great ambiguity in the terms
“conscious” and “unconscious.” In one sense no definition of
Consciousness can be satisfactory, since it designates an ultimate
fact, which cannot therefore be made more intelligible than it is
already. In another sense no definition is needed, since every one
knows what is meant by saying, “I am conscious of such a change,
or such a movement.” It is here the equivalent of Feeling. To be
conscious of a change, is to feel a change. If we desire to express
it in physiological terms, we must define Consciousness--“a function
of the organism”; and this definition we shall find eminently useful,
because the organism being a vital mechanism, and the integrity of that
mechanism being necessary for the integrity of the function, while
every variation of the mechanism will bring a corresponding variation
of the function, we shall have an objective guide and standard in
our inquiries. Organisms greatly differ in complexity, yet because
they also agree in the cardinal conditions of Vitality, among which
Sensibility is one, we conclude that they all have Feeling; but the
Feeling of the one will differ from that of another, according to the
complexity of the sentient mechanism in each. The perfection of this
mechanism lies in the co-ordination of its parts, and the consensus of
its sentient activities; any disturbance of that consensus must cause
a modification in the total consciousness; and when the disturbance
is profound the modification is marked by such terms as “insanity,”
“loss of consciousness,” “insensibility.” These terms do not imply
that the sentient organs have lost their Sensibility, but only that
the disturbed mechanism has no longer its normal consensus, no longer
its normal state of Consciousness. Each organ is active in its own
way so long as its own mechanism is preserved; but the united action
of the organs having been disturbed, their _resultant_ function has
been altered. Hence in a fit of Epilepsy there is a complete absence
of some normal reactions, with exaggeration of others. In a state of
Coma there is no spontaneity--none of the manifold adaptations of the
organism to fluctuating excitations, external and internal, observable
in the normal state. The organism still manifests Sensibility--but
this is so unlike the manifestations when its mechanism is
undisturbed (and necessarily so since the Sensibility varies with
the mechanism) that it is no longer called by the same name. In the
normal organism Sensibility means Feeling, or Consciousness; but in
the abnormal organism there is said to be a “loss of Consciousness.”
What the physiologist or the physician means by the phrase “loss of
Consciousness” is intelligible, and for his purposes unobjectionable.
He observes many organic processes going on undisturbed--the
unconscious patient breathes, secretes, moves his limbs, etc. These
processes are referred to the parts of the mechanism which are not
disturbed; they are obviously independent of that adjustment of the
mechanism which by its _consensus_ has the special resultant named
Consciousness; he therefore concludes that these, and many other
organic processes, which are neither accompanied nor followed by
_discriminated_ feelings, are the direct consequences of the stimulated
mechanism. He never hesitates to adopt the popular language, and say,
“We sometimes act unconsciously, perceive unconsciously, and even think
unconsciously, all by the simple reflex of the mechanism.”
Now observe the opening for error in this language. The actions are
said to go on unconsciously, and, because unconsciously, as pure
reflexes, which are then assigned to an insentient mechanism, and
likened to the actions of machines. But, as I hope hereafter to make
evident, the reflex mechanism necessarily involves Sensibility; and
therefore reflex actions may be unaccompanied by Consciousness--in
one meaning of that term--without ceasing to be sentient, the feelings
are operative, although not discriminated. On the other hand, there is
another and very general meaning of the term Consciousness, which is
the equivalent of Sentience.
51. In discussing Automatism, or the Reflex Theory, it is absolutely
necessary that we should first settle the meaning we assign to the
term Consciousness. The laxity with which the term is used may be seen
in the enumeration occupying six pages of Professor Bain’s account of
the various meanings. Psychology is often said to be “the science of
the facts of Consciousness”; and the Brain is often assigned as “the
organ of Consciousness.” Yet there are many mental processes, and many
cerebral processes, which are declared to be unconscious. Obviously if
Consciousness is the function of the Brain, there can be no cerebral
activity which is unconscious; just as there can be no activity of the
lungs which is not respiratory. Usage therefore points to a general
and a special sense of the term. The general usage identifies it
with Sensibility, in its subjective aspect as Sentience, including
all psychical states, both those classed under Sensation, and those
under Thought. These states are the “facts of consciousness” with
which Psychology is occupied. In the special usage it is distinguished
from all other psychical states by a peculiar reflected feeling of
Attention, whereby we not only _have_ a sensation, but also _feel_ that
we have it; we not only think, but are conscious that we are thinking;
not only act, but are conscious of what we do. It is this which Kant
indicates when he defines it “the subjective form accompanying all our
conceptions (_Begriffe_)”; and Jessen when he defines it “the internal
knowing of our knowing, an in itself reflected knowing.”[212]
52. We shall often have to recur to this general and this special
meaning, both of which are too firmly rooted for any successful attempt
to displace them. The fact that some organic processes and some
mental processes take place now consciously and now unconsciously,
i. e. now with the feeling of reflected attention, and now with no
such feeling, assuredly demands a corresponding expression; nor, in
spite of inevitable ambiguities, is there ground for regretting that
the expression chosen should be only an extension of the expression
already adopted for all other states of Sentience. A sentient or
conscious state can only be a state of the sentient organism, itself
the unity of many organs, each having its Sensibility. There is
more or less consensus, but there is no introduction of a new agent
within the organism, converting what was physical impression into
mental reaction. From first to last there has been nothing but
neural processes, and combinations of such processes--which, viewed
subjectively, are sentient processes. Thus the gradations of sensitive
reaction are Sentience, Consentience, and Consciousness, which are
represented in the Logic of Feeling and the Logic of Signs. The
familiar term Conscience will then represent the Logic of Conduct.
Thus understood, we may say that a man sometimes acts unconsciously,
or thinks unconsciously, although his action and thought are ruled
by Consentience, as he sometimes acts and thinks unconscientiously,
although he is not without obedience to Conscience on other occasions.
The feeling which determines an action is _operative_, although it
may not be _discriminated_ from simultaneous feelings. When this
is the case, we say the feeling is unconscious; but this no more
means that it is a purely physical process taking place outside the
sphere of Sentience, than the immoral conduct of a man would be said
to be mechanical, and not the conduct of a moral agent. There is
undoubtedly a marked distinction expressed in the terms Consciousness
and Unconsciousness, but it is not that of contrasts such as Mental
and Physical, it is that of grades such as Light and Darkness. Just
as Darkness is a positive optical sensation very different from mere
privation--just as it replaces the sensation of Light, blends with
it, struggles with it, and in all respects differs from the _absence_
of all optical sensibility in the skin; so Unconsciousness struggles
with, blends with, and replaces Consciousness in the organism, and is
a positive state of the sentient organism, not to be confounded with a
mere negation of Sentience; above all, not to be relegated to merely
mechanical processes.
52 _a_. Remember that, strictly speaking, Consciousness is a
psychological not a physiological term, and is only used in Physiology
on the assumption that it is the subjective _equivalent_ of an
objective process. To avoid the equivoque of “unconscious sensation,”
we may substitute the term “unconscious neural process”; and as all
neural processes imply Sensibility, which in the subjective aspect is
Sentience, we say that Sentience has various modes and degrees--such
as Perception, Ideation, Emotion, Volition, which may be conscious,
sub-conscious, or unconscious. When Leibnitz referred to the fact of
“obscure ideas,” and modern writers expressed this fact as “unconscious
cerebration,” the first phrase did not imply a process that was other
than mental, the second phrase did not imply a process that was other
than physiological: both indicated a mode of the process known as
Consciousness under other modes. There are different neural elements
grouped in Ideation and Emotion; there are different neural elements
grouped in Consciousness, Sub-consciousness, and Unconsciousness; but
one tissue with one property is active in all.
53. The nervous organism is affected as a whole by every affection
of its constituent parts. Every excitation, instead of terminating
with itself--as is the case in most physical processes--or with the
motor impulse it excites, is propagated throughout the continuous
tissue, and thus sends a _thrill_ throughout the organism. The wave
of excitation in passing onwards beats against variously grouped
elements--temporary and permanent centres--disturbing their balance
more or less, and liberating the energy of some, increasing the tension
of others, necessarily affecting all. Those groups which have their
energy liberated set up processes that are either _discriminated_
as sensations, or are blended with the general stream, according
to their _relative_ energy in the consensus. Thus the impulse on
reaching the centres for the heart, lungs, legs, and tail excites
the innervation of these organs; but as these are only parts of the
organism, and as all the parts enter the consensus, and Consciousness
is the varying resultant of this ever-varying consensus, the
thrill which any particular stimulus excites will be unconscious,
sub-conscious, or conscious, in proportion to the extent of the
_irradiated_ disturbance, which will depend on the statical conditions
of the centres at the moment. A sound sends a thrill which excites
emotion, causes the heart to beat faster, the muscles to quiver, the
skin-glands to pour forth their secretion; yet this same sound heard
by another man, or the same man under other conditions, physical or
historical, merely sends a faint thrill, just vivid enough to detach
itself as a sensation from the other simultaneous excitations; and
the same sound may excite a thrill which is so faint and fugitive as
to pass unconsciously. Physiological and psychological inductions
assure us that these are only differences of degree. The same kind
of physiological effect accompanies the conscious and unconscious
state. Every sensory impression, no matter whether discriminated or
not, affects the circulation and develops heat. The blood-vessels of
the part impressed expand, vessels elsewhere contract--a change in
the blood pressure has been effected, which of course implies that
the whole organism has been affected. Delicate instruments show that
at the time a sensation is produced the temperature of the brain is
raised. The same is true of ideation. Mosso has invented a method of
registering the effect of thought on the circulation. He finds ideation
accompanied by a contraction of the peripheral vessels proportionate
to the degree of intellectual effort. A young man translating Greek
showed greater contraction than when he was translating Latin. During
sound sleep--when we are said to be unconscious--sudden noises
always cause contraction of the peripheral vessels. Psychological
observation assures us that the conscious and unconscious states
were both consentient, and were both operative in the same degree.
The absorbed thinker threads his way through crowded streets, and is
sub-conscious and unconscious of the various sights, sounds, touches,
and muscular movements which make up so large a portion of his sentient
excitation at the time; yet he deftly avoids obstacles, hears the
sound of a hurried step behind him, recognizes an interesting object
directly it presents itself, and can even recall in Memory many of the
uninteresting objects which he passed in sub-conscious and unconscious
indifference.
54. On all grounds, therefore, we must say that between conscious,
sub-conscious, and unconscious states the difference is only of
degree of complication in the neural processes, which by relative
preponderance in the consensus determine a relative discrimination. We
can only discriminate one thrill at a time; but the neural excitations
simultaneously pressing towards a discharge are many; and the
conditions which determine now this, and now the other excitation to
predominate by its differential pressure, are far beyond any mechanical
estimate. I mention this because the advocates of the Reflex Theory
maintain that the neural processes are the same whether a sensation be
produced or not; and that since the same actions follow the external
stimulation whether sensation be produced or not, this proves the
actions to be purely mechanical. I reply, the neural processes are
_not_ the same throughout in the two cases--otherwise the effects would
be the same. You might as well say, “Since the explosion of the gun
is the same, whether shotted or not, a blank cartridge will kill”;
but if you tell me that your gun killed the bird, I declare that the
cartridge was _not_ a blank one. Whether the explosion of the gun
_also_ produced terror in one bystander, curiosity in a second, and
attracted no notice from a third, will be altogether another matter.
In like manner the sensory impression which determines a movement may
or may not be accompanied or followed by _other_ sentient states; the
fact of such movement is evidence of its sentient antecedent; and an
external stimulus that will produce _this_ neural process, and this
consequent movement, must produce a feeling, although not necessarily a
discriminated sensation. Now since, for discrimination, _other_ neural
processes must co-operate, we cannot say that in the two cases _all_
the neural processes have been the same throughout; nor because of this
difference can we say that the process of the undiscriminated sensation
is a mechanical, not a sentient process. In the next problem this point
will be argued more fully.
55. The need of recognizing Consciousness and Consentience as degrees
of energy and complexity in sentient states is apparent when we
consider animal phenomena. Has a bee consciousness? Has a snail
volition? or are they both insentient mechanisms? All inductions
warrant the assertion that a bee has thrills propagated throughout its
organism by the agency of its nerves; and that some of these thrills
are of the kind called sensations--even discriminated sensations.
Nevertheless we may reasonably doubt whether the bee has sentient
states resembling otherwise than remotely the sensations, emotions,
and thoughts which constitute human Consciousness, either in the
general or the special sense of that term. The bee feels and reacts on
feelings; but its feelings cannot closely resemble our own, because
the conditions in the two cases are different. The bee may even be
said to think (in so far as Thought means logical combination of
feelings), for it appears to form Judgments in the sphere of the Logic
of Feeling--το νοητικὸν; although incapable of the Logic of Signs--το
διανοητικον. We should therefore say the bee has Consentience, but
not Consciousness--unless we accept Consciousness in its _general_
signification as the equivalent of Sentience. The organism of the bee
differs from that of a man, as a mud hut from a marble palace. But
since underlying these differences there are fundamental resemblances,
the functions of the two will be fundamentally alike. Both have the
function of Sentience; as mud hut and palace have both the office of
sheltering.
56. The question of Volition will occupy us in the next chapter.
Restricting ourselves here to that of Consciousness, and recalling
the distinction of the two meanings of the term, we now approach
the question of Unconsciousness. Are we to understand this term as
designating a purely physical state in contrast to the purely mental
state of Consciousness; or only as designating a difference of degree?
This is like asking whether Light and Darkness are both optical
feelings, or one an optical feeling and the other a physical process?
On the Reflex Theory, no sooner does a vital and mental process pass
from the daylight of Consciousness, or twilight of Sub-consciousness,
into the darkness of Unconsciousness, than the whole order of phenomena
is abruptly changed, they cease to be vital, mental, and lapse into
physical, mechanical processes. The grounds of this conclusion are,
first, the unpsychological assumption that the unconscious state is
out of the sphere of Sentience; and secondly, the unphysiological
assumption that the Brain is the only portion of the nervous system
which has the property of Sensibility. Restate the conclusion in
different terms and its fallacy emerges: “organic processes suddenly
cease to be organic, and become purely physical by a slight change
in their _relative_ position in the consensus; the organic process
which was a conscious sensation a moment ago, when its energy was not
balanced by some other process, suddenly falls from its place in the
group of organic phenomena--sentient phenomena--to sink into the group
of inorganic phenomena now that its energy is balanced.” Consider the
parallel case of Motion and Rest in the objective sphere. They are two
functions of the co-operant forces, one dynamic, the other static;
although markedly distinguishable as functions, we know that they are
simply the co-operant forces now unbalanced and now balanced; what
we call Rest is also a product of moving forces, each of which is
operant, and will issue in a definite resultant when its counter-force
is removed. Motion and Rest are correlatives, and both belong to the
sphere of Kinetics. In like manner Consciousness and Unconsciousness
are correlatives, both belonging to the sphere of Sentience.[213] Every
one of the unconscious processes is operant, changes the general state
of the organism, and is capable of at once issuing in a discriminated
sensation when the force which balances it is disturbed. I was
unconscious of the scratch of my pen in writing the last sentence, but
I am distinctly conscious of every scratch in writing this one. Then,
as now, the scratching sound sent a faint thrill through my organism,
but its relative intensity was too faint for discrimination; now that I
have redistributed the co-operant forces, by what is called an act of
Attention, I hear distinctly every sound the pen produces.
57. The inclusion of Sub-consciousness within the sentient sphere is
obvious; the inclusion of Unconsciousness within that sphere may be
made so, when we consider its modes of production, and compare it
with the extra-sensible conception of molecules and atoms. The Matter
which is sensible as masses, may be resolved into molecules, which lie
beyond the discrimination of sense; and these again into atoms, which
are purely ideal conceptions; but because molecules are _proved_, and
atoms are _supposed_, to have material properties, and to conform to
sensible canons of the objective world, we never hesitate to class them
under the head of Matter; nor do we imagine that in passing beyond the
discrimination of Sense they lose their objective significance. They
are still physical, not mental facts. So with Sentience: we may trace
it through infinite gradations from Consciousness to Sub-consciousness,
till it fades away in Unconsciousness; but from first to last the
processes have been those of a sentient organism; and by this are
broadly distinguished from all processes in anorganisms. The movement
of a limb has quite different modes of production from the movement of
a wheel; and among its modes must be included those of Sensibility,
a peculiarly vital property. Oxidation may be slow or rapid,
manifesting itself as combustion, heat, or flame, but it is always
oxidation--always a special chemical phenomenon. And so the neural
process of Sentience, whether conscious, sub-conscious, or unconscious,
is always a state of the sentient organism. If a material process does
not change its character, and become spiritual, on passing beyond the
range of sensible appreciation, why should a psychical process become
material on passing beyond the range of discrimination? If we admit
molecules as physical units, sentient tremors are psychical units.
The extra-sensible molecules have indeed their subjective aspect,
and only enter perception through the “greeting of the spirit.” The
sentient tremors have also their objective aspect, and cannot come
into existence without the neural tremors, which are their physical
conditions.
58. It is only by holding fast to such a conception that we can escape
the many difficulties and contradictions presented by unconscious
phenomena, and explain many physiological and psychological processes.
Descartes--followed by many philosophers--identified Consciousness
with Thought. To this day we constantly hear that to have a sensation,
and to be conscious of it, is one and the same state; which is only
admissible on the understanding that Consciousness means Sentience,
and Sentience the activity of the nervous system viewed subjectively.
Leibnitz pointed out that we have many psychical states which are
unconscious states--to have an idea and be conscious of it, are, he
said, not one but two states. The Consciousness by Descartes erected
into an essential condition of Thought, was by Leibnitz reduced to an
accompaniment which not only may be absent, but in the vast majority
of cases is absent. The teaching of most modern psychologists is
that Consciousness forms but a small item in the total of psychical
processes. Unconscious sensations, ideas, and judgments are made to
play a great part in their explanations. It is very certain that in
every conscious volition--every act that is so characterized--the
larger part of it is quite unconscious. It is equally certain that
in every perception there are unconscious processes of reproduction
and inference--there is much that is _implicit_, some of which cannot
be made explicit--a “middle distance” of sub-consciousness, and a
“background” of unconsciousness. But, throughout, the processes are
those of Sentience.
59. Unconsciousness is by some writers called _latent_ Consciousness.
Experiences which are no longer manifested are said to be stored up in
Memory, remaining in the Soul’s picture-gallery, visible directly the
shutters are opened. We are not conscious of these feelings, yet they
exist as latent feelings, and become salient through association. As a
metaphorical expression of the familiar facts of Memory this may pass;
but it has been converted from a metaphor into an hypothesis, and we
are supposed to _have_ feelings and ideas, when in fact we have nothing
more than a modified _disposition_ of the organism--temporary or
permanent--which when stimulated will respond in this modified manner.
The modification of the organism when permanent becomes hereditary; and
its response is then called an instinctive or automatic action. And as
actions pass by degrees from conscious and voluntary into sub-conscious
and sub-voluntary, and finally into unconscious and involuntary, we
call them volitional, secondarily automatic, and automatic. If any one
likes to say the last are due to latent consciousness, I shall not
object. I only point to the fact that the differences here specified
are simply differences of degree--all the actions are those of the
sentient organism.
60. Picture to yourself this sentient organism incessantly stimulated
from without and from within, and adjusting itself in response to such
stimulations. In the blending of stimulations, modifying and arresting
each other, there is a fluctuating “composition of forces,” with
ever-varying resultants. Besides the stream of direct stimulations,
there is a wider stream of indirect or reproduced stimulations.
Together with the present sensation there is always a more or less
complex group of revived sensations, the one group of neural tremors
being organically stimulated by the other. An isolated excitation is
impossible in a continuous nervous tissue; an isolated feeling is
impossible in the consensus or unity of the sentient organism. The term
Soul is the personification of this complex of present and revived
feelings, and is the substratum of Consciousness (in the general
sense), all the particular feelings being its _states_. To repeat an
illustration used in my first volume, we may compare Consciousness to
a mass of stationary waves. If the surface of a lake be set in motion
each wave diffuses itself over the whole surface, and finally reaches
the shores, whence it is reflected back towards the centre of the lake.
This reflected wave is met by the fresh incoming waves, there is a
blending of the waves, and their product is a pattern on the surface.
This pattern of stationary waves is a fluctuating pattern, because of
the incessant arrival of fresh waves, incoming and reflected. Whenever
a fresh stream enters the lake (i. e. a new sensation is excited from
without), its waves will at first pass over the pattern, neither
disturbing it nor being disturbed by it; but after reaching the shore
the waves will be reflected back towards the centre, and there will
more or less modify the pattern.
CHAPTER V.
VOLUNTARY AND INVOLUNTARY ACTIONS.
61. Much of what has been said in the preceding chapter respecting
the passive side of the organism is equally applicable to the active
side. Our actions are classed as voluntary and involuntary mainly in
reference to their being consciously or unconsciously performed; but
not wholly so, for there are many involuntary actions of which we are
distinctly conscious, and many voluntary actions of which we are at
times sub-conscious and unconscious. I do not propose here to open the
long and arduous discussion as to what constitutes Volition, my present
purpose being simply that of fixing the meaning of terms, so that the
question of Automatism may not be complicated by their ambiguities.
“Voluntary” and “involuntary” are, like “conscious” and “unconscious,”
correlative terms; but commonly, instead of being understood as
indicating differences of degree in phenomena of the same order, they
are supposed to indicate differences of kind--a new agent, the Will,
being understood in the one case to direct the Mechanism which suffices
without direction in the other.
62. This interpretation is unphysiological and unpsychological,
since it overlooks the fact that both voluntary and involuntary
actions belong to the same _order_ of phenomena, i. e. those of the
sentient organism. Both involve the same _efficient_ cause, i. e.
co-operant conditions. We draw a line of demarcation between the two
abstractions--as between all abstractions--but the concrete processes
they symbolize have no such demarcation. Just as the thought which at
one moment passes unconsciously, at another consciously, is in itself
the same thought, and the same neural process; so the action which at
one moment is voluntary, and at another involuntary, is itself the same
action, performed by the same mechanism. The incitation which precedes,
and the feeling which accompanies the action, belong to the accessory
mechanisms, and may be replaced by other incitations and other
feelings; as the fall of an apple is the same event, involving the same
conditions, i. e. efficient cause, whether the _occasional_ cause be a
gust of wind or the gardener’s scissors, and whether the fall be seen
and heard or not. I may utter words intentionally and consciously, and
I may utter the same words automatically, unconsciously; I may wink
voluntarily, and wink involuntarily. There are terms to express these
differences; but they do not express a difference in the efficient
agencies.
63. Many writers seem to think that the involuntary actions belong
to the physical mechanical order, because they are not stimulated by
cerebral incitations, and cannot be regulated or controlled by such
incitations--or as the psychologists would say, because Consciousness
in the form of Will is no agent prompting and regulating such actions.
But I think this untenable. The actions cannot belong to the mechanical
order so long as they are the actions of a vital mechanism, and so long
as we admit the broad distinction between organisms and anorganisms.
Whether they have the special character of Consciousness or not,
they have the general character of sentient actions, being those
of a sentient mechanism. And this becomes the more evident when we
consider the gradations of the phenomena. Many, if not all, of those
actions which are classed under the involuntary were originally of
the voluntary class--either in the individual or his ancestors; but
having become permanently organized dispositions--the pathways of
stimulation and reaction having been definitely established--they have
lost that volitional element (of hesitation and choice) which implies
regulation and control. But even here a slight change in the habitual
conditions will introduce a disturbance in the process which may
awaken Consciousness, and the sense of effort, sometimes even causing
control. An instinctive or an automatic action may be thus changed,
or arrested. Take as an example one of the unequivocally automatic
actions, that of Breathing. It is called automatic because, like the
actions of an automaton, it is performed by a definitely constructed
mechanism, always working in the same way when stimulated and left to
itself. There must of course be a sense of effort in every impulse
which has resistance to overcome, organs to be moved; but the mechanism
of Breathing is so delicately adjusted, that the sense of effort is
reduced to a minimum, and we are unconscious of it, or sub-conscious
of it. Nevertheless, without altering the rate or amplitude of the
inspirations and expirations, we become distinctly conscious of them,
and, moreover, within certain limits we can control them, so that the
Breathing passes from the involuntary to the voluntary class.
64. Pass on to other examples. What action can be more involuntary than
the rhythmic movements of the heart and the contractions of the iris?
Compared with the actions of the tongue or limbs, these seem riveted
by an iron necessity, freed from all consciousness and control. Yet
the movements of the heart are not only stimulated by sensations and
thoughts, they are also capable of being felt; and the movements both
of heart and iris are not wholly removed from our control. That we do
not habitually control (that is, _interfere_ with) the action of the
heart, the contraction of the iris, or the activity of a gland, is
true; it is on this account that such actions are called involuntary;
they obey the immediate stimulus. But it is an error to assert that
these actions _cannot_ be controlled, that they are altogether beyond
the interference of other centres, and cannot by any effort of ours
be modified. It is an error to suppose these actions are essentially
distinguished from the voluntary movement of the hands. We have
acquired a power of definite direction in the movements of the hands,
which renders them obedient to our will; but this acquisition has been
of slow laborious growth. If we were asked to use our toes as we use
our fingers--to grasp, paint, sew, or write with them, we should find
it not less impossible to control the movements of the toes in these
directions, than to contract the iris, or cause a burst of perspiration
to break forth. Certain movements of the toes are possible to us; but
unless the loss of our fingers has made it necessary that we should
use our toes in complicated and slowly acquired movements, we can do
no more with them than the young infant can do with his fingers. Yet
men and women have written, sewed, and painted with their toes. All
that is requisite is that certain links should be established between
sensations and movements; by continual practice these links _are_
established; and what is impossible to the majority of men, becomes
easy to the individual who has acquired this power. This same power
can be acquired over what are called the organic actions; nevertheless
the habitual needs of life do not _tend_ towards such acquisition,
and without some strong current setting in that direction, or some
peculiarity of organization rendering it easy, it is never acquired.
In ordinary circumstances the number of those who can write with their
toes is extremely rare, the urgent necessity which would create such a
power being rare; and rare also are the examples of those who have any
control over the movement of the iris, or the action of a gland; but
both rarities exist.
It would be difficult to choose a more striking example of reflex
action than the contraction of the iris of the eye under the stimulus
of light;[214] and to ordinary men, having no link established which
would guide them, it is utterly impossible to close the iris by any
effort. It would be not less impossible to the hungry child to get
on the chair and reach the food on the table, until that child had
_learned_ how to do so. Yet there are men who have learned how to
contract the iris. The celebrated Fontana had this power; which is
possessed also by a medical man now living at Kilmarnock--Dr. Paxton--a
fact authenticated by no less a person than Dr. Allen Thomson.[215] Dr.
Paxton can contract or expand the iris at will, without changing the
position of his eye, and without an effort of adaptation to distance.
To move the ears is impossible to most men. Yet some do it with ease,
and all could learn to do it. Some men have learned to “ruminate” their
food; others to vomit with ease; and some are said to have the power of
perspiring at will.[216] Now, if once we recognize a link of sensation
and motion, we recognize a possible source of control; and if the
daily needs of life were such that to fulfil some purpose the action
of the heart required control, we should learn to control it. Some
men have, without such needs, learned how to control it. The eminent
physiologist, E. F. Weber of Leipzig, found that he could completely
check the beating of his heart. By suspending his breath and violently
contracting his chest, he could retard the pulsations; and after
three or five beats, unaccompanied by any of the usual sounds, it was
completely still. On one occasion he carried the experiment too far,
and fell into a syncope. Cheyne, in the last century, recorded the case
of a patient of his own who could at will suspend the beating of his
pulse, and always fainted when he did so.
65. It thus appears that even the actions which most distinctly bear
the character recognized as involuntary--uncontrollable--are only so
because the ordinary processes of life furnish no necessity for their
control. We do not learn to control them, though we could do so, to
some extent; nor do we learn to control the motions of our ears,
although we could do so. And while it appears that the involuntary
actions can become voluntary, it is familiar to all that the voluntary
actions tend, by constant repetition, to become involuntary. Thus
involuntary actions, under certain limitations, may be controlled; on
the other hand, the voluntary are incapable of being controlled under
the urgency of direct stimulation. Both are reflexes.
Inasmuch as almost all actions are the products of stimulated
nerve-centres, it is obvious that these actions are reflex--reflected
from those centres. It matters not whether I wink because a sensation
of dryness, or because an idea of danger, causes the eyelid to close:
the act is equally reflex. The nerve-centre which supplies the eyelid
with its nerve has been stimulated; the stimuli may be various, the
act is uniform. At one time the stimulus is a sensation of dryness,
at another an idea of danger, at another the idea of communicating
by means of a wink with some one present; in each case the stimulus
is reflected in a muscular contraction. Sensations excite other
sensations; ideas excite other ideas; and one of these ideas may issue
in an action of control. But the restraining power is limited, and
cannot resist a certain degree of urgency in the original stimulus. I
can, for a time, restrain the act of winking, in spite of the sensation
of dryness; but the reflex which sets going this restraining action
will only last a few seconds; after which, the urgency of the external
stimulus is stronger than that of the reflex feeling--the sensation of
dryness is more imperious than the idea of resistance--and the eyelid
drops.
If a knife be brought near the arm of a man who has little confidence
in the friendly intentions of him that holds it, he shrinks, and the
shrinking is “involuntary,” i. e. in spite of his will. Let him have
confidence, and he does not shrink, even when the knife touches his
skin. The idea of danger is not excited in the second case, or if
excited, is at once banished by another idea. Yet this very man, who
can thus repress the involuntary shrinking when the knife approaches
his arm, cannot repress the involuntary winking when the same friend
approaches a finger to his eye. In vain he prepares himself to resist
that reflex action; in vain he resolves to resist the impulse; no
sooner does the finger approach, than down flashes the eyelid. Many
men, and most women, would be equally unable to resist shrinking on the
approach of a knife: the association of the idea of danger with the
knife would bear down any previous resolution not to shrink. It is from
this cause that timorous women tremble at the approach of firearms. An
association is established in their minds which no idea is powerful
enough to loosen. You may assure them the gun is not loaded; “_that_
makes very little difference,” said a naïve old lady to a friend of
mine. They tremble, as the child trembles when he sees you put on the
mask. These illustrations show that the urgency of any one idea may,
like the urgency of a sensation, bear down the resistance offered by
some other idea; as the previous illustrations showed that an idea
could restrain or control the action which a sensation or idea would
otherwise have produced. According to the doctrines current, the Will
is said to be operative when an idea determines an action; and yet all
would agree that the winking which was involuntary when the idea of
danger determined it, was voluntary when the idea of communicating with
an accomplice in some mystification determined it.
66. There is no real and essential distinction between voluntary and
involuntary actions. They all spring from Sensibility. They are all
determined by feeling. It is convenient, for common purposes, to
designate some actions as voluntary; but this is merely a convenience;
no psychological nor physiological insight is gained by it; an analysis
of the process discloses no element in a voluntary action which is
not to be found in an involuntary action--except in the origin or
degree of stimulation. In ordinary language it is convenient to mark a
distinction between my raising my arm because I will to raise it for
some definite purpose, and my raising it because a bee has stung me; it
is convenient to say, “I _will_ to write this letter,” and “this letter
is written against my will--I have no will in the matter.” But Science
is more exacting when it aims at being exact; and the philosopher,
analyzing these complex actions, will find that in each case certain
muscular groups have been set in action by different sensational or
ideational stimuli. The action itself is that of a neuro-muscular
mechanism, which mechanism works in the same way, whatever be the
source of the original impulse. The stimulation may be incited
directly from the periphery, or indirectly from a remote centre; and
the action may be arrested by a peripheral or central stimulation:
the reflex which ordinarily follows the excitation of a sensory nerve
will be modified, or arrested, if some other nerve be at the same time
stimulated. (See Law of Arrest, _Prob._ II. § 190.)
67. All actions are reflex, all are the operations of a mechanism,
all are sentient, because the mechanism has Sensibility as its vital
property. In thus preserving the integrity of the order of vital
phenomena, and keeping them classified apart from physical and chemical
phenomena, we by no means set aside the useful distinctions expressed
in the terms voluntary and involuntary; any more than we set aside the
distinction of vertebrate and invertebrate when both are classed under
Animal, and separated from Plant, or Planet.
The mechanisms of the special Senses respond in special reactions;
the mechanisms of special actions have also their several responses.
The tail responds to stimulation with lateral movements, the chest
with inspiration and expiration, and so on. These responses are called
automatic, and have this in common with the actions of automata that
they are uniform, and do not need the co-operation of Consciousness,
though they do need the operation of Sensibility, and are thereby
distinguished from the actions of automata. The facial muscles, and
the limbs, also respond to stimulation in uniform ways, but owing to
the varieties of stimulation the actions are more variable, and have
more the character of volitional movements. With this greater freedom
of possible action comes the eminently mental character of _choice_.
In the cerebral rehearsal of an act not yet performed--its mental
prevision--as when we intend to do something, yet for the moment
arrest the act, so that there is only a nascent excitation of the
motor process, there is a peculiar state of Consciousness expressive
of this state of the mechanism: we call the prevision a _motive_--and
it becomes a _motor_ when the intention is realized, the nascent
excitation becomes an unchecked impulse. The abstract of all motives we
call Will. A motive is a volition in the sphere of the Intellect. In
the sphere of Emotion it is a motor. Hence we never speak of the Will
of a mollusc, or the motives of an insect, only of their sensations and
motors. Yet it is obvious that the reflex in operation when a snail
shrinks at the approach of an object is essentially similar to the
reflex in operation when the baby shrinks, and this again is still more
similar to that in operation when the boy shrinks: the boy has the idea
of danger, which neither baby nor snail can have; the idea is a motive,
which can be controlled by another idea; the baby and the snail can
have no such motive, no such control--are they therefore automata?
68. If I see that a donkey has wandered into my garden, the motive
which determines me to take a stick and with it drive the donkey
away is a cerebral rehearsal of the effects which will follow my
act. The sight of the donkey has roused disagreeable feelings,
and these suggest possible means of alleviation; out of these
possibilities--reproductions of former experiences--I choose one.
But if I seize the stick with which some one is threatening me, I do
not pause to choose, I snatch automatically without hesitation. Yet
this unreflecting automatic act is itself as truly volitional as my
seizing the stick to drive away the donkey--it is the motor which has
been organized in me by previous experiences--it is the consequence
of an emotion, not of a deliberation; and it has not been determined
by any clear prevision of consequences. Feeling inspires, and feeling
guides my movements, so that if my snatch has missed the stick, I
snatch again, or duck under. This is the kind of Volition we ascribe
to animals. It is a great part of our own. By insensible degrees, acts
which originally were prompted by motives sink into the automatic
class prompted by motors. When an angry man snatches up a knife, doffs
bystanders aside, and rushes on his enemy to stab him, he does not
distinctly prefigure the final result, he only obeys each motor, and
is conscious of each step; but had he planned the murder he would have
foreseen the end, and this prevision would have been the motive. The
angry man is struck with horror at the sight of the bleeding corpse,
and passionately declares he did not _mean_ to kill. Nor did he will
the consequences of his act, yet he certainly willed each separate
step--he recognized the knife, saw the bystanders, knew they would
interfere with him, willed to push them aside. He may be right in
declaring that the act was involuntary; but assuredly it was not purely
mechanical.
69. Again, we are not conscious of the separate sensations which guide
speech or writing; we cannot properly be said to will the utterance
of each tone, or the formation of each letter. Are these processes
mechanical and not volitional? By no means. We know that they were
laboriously learned by long tentative efforts, each of which was
accompanied by distinct consciousness. We also know that now when the
mechanism is so easy in its adjustment as to suggest automatism, there
needs but a slight alteration in the conditions to make us distinctly
conscious of the processes--the wrong word spoken, or one letter ill
formed, suffices to arrest the easy working of the mechanism. A similar
mechanism operates in thinking, which also lapses from the conscious
and voluntary to the unconscious and involuntary state. The logical
process of Judgment is as purely a reflex from one neural group to
another, as the physiological process of co-ordination. In ordinary
thinking we are as little conscious of the particular steps--our
interest being concentrated on the result--as we are of the particular
stages of an action. The adjustments of the mechanism of Reproduction
and Association are _set_ going by a motive, and _kept_ going by
psychological motors. And here--as in bodily actions--there is often
a conflict between motive and motors--between the foreseen result,
and the available means of reaching it--the motors usually prevailing
because they represent the active side of the mechanism. Thus when an
oculist wishes to examine a patient’s eye, he does not tell him to give
a particular direction to his eye, knowing that the _motive_ to do so
will not suffice; instead of this he simply moves his own hand in the
desired direction, certain that the eye will by reflex irresistibly
follow it. Nay, there are sometimes such anomalies of innervation
that the eye, instead of obeying the motive, moves in a contrary
direction. Meschede mentions a patient whose movements were mostly of
this anomalous kind: when he willed to move the eyes to the right, they
moved to the left; when he willed to move them up, they moved down. It
was thus also with his hands and feet. Yet he was distinctly conscious
that his intention had been frustrated, and that he acted “because he
could not help it.”[217] How insensibly a motive sinks into a motor,
that is to say, a voluntary into an involuntary act, may be recognized
in speech, writing, singing, walking, etc., and in the incessant
movements of the eye in fixing objects. Aubert has well remarked
that we only give definite movements to the eye when we wish to see
an object distinctly. Whenever the indistinct vision suffices--as in
walking through the streets occupied in conversation or thought--we
make no such movements; but no sooner does any object excite our
attention, than the effort to fix that object at once excites the
necessary reflex.[218]
70. By the Will, then, we must understand the abstract generalized
expression of the impulses which determine actions, when those
impulses have an ideal origin; by Volition the still more generalized
expression of all impulses which determine actions. The one class is
that of _motives_ with ideal elements; the other that of _motors_ with
sensational or emotional elements. But both are mental states, both
are neural processes in a sentient organism; neither is mechanical,
except in so far as all actions are expressible in mechanical terms.
For convenience we class actions as reflex, automatic, involuntary,
unconscious, voluntary, and conscious. If we separate the reflex
from the voluntary, we need not therefore dissociate the former from
Sensibility; and the reason why we ought not to separate it is that we
know it to be sense-guided from first to last, although the sensations
may escape discrimination. The feeling of Effort, which was formerly
felt when an action was performed, may have become so minimized
that it is too faint for more than a momentary consciousness, too
evanescent for the memory to retain it; yet the feeling must always
be operant when its mechanism is in action. The ease with which the
mechanism works does not change the adjustment of its elements, nor
alter its character. The facile unobtrusive performance of a vital
function does not change it from a vital to a mechanical act. Mr.
Spencer seems to me to express himself ambiguously when he says:
“Just as any set of psychical changes originally displaying Memory,
Reason, and Feeling cease to be conscious, rational, and emotional
as fast as they by repetition grow closely organized, so do they at
the same time pass beyond the sphere of Volition. Memory, Reason,
Feeling, and Will disappear in proportion as psychical changes become
automatic”[219]--for while it is perfectly true that we only call those
psychical changes “automatic” which have lost the special qualities
called “conscious, rational, and emotional,” it is not less true that
they remain from first to last _psychical_ changes, and are thereby
distinguished from _physical_ changes. To suppose that they pass from
the psychical to the physical by frequent repetition would lead to the
monstrous conclusion that when a naturalist has by laborious study
become so familiarized with the specific marks of an animal or plant
that he can recognize at a glance a particular species, or recognize
from a single character the nature of the rest, the rapidity and
certainty of this judgment proves it to be a mechanical, not a mental
act. The intuition with which a mathematician sees the solution of a
problem would then be a mechanical process, while the slow and bungling
hesitation of the tyro in presence of the same problem would be a
mental process: the perfection of the organism would thus result in its
degradation to the level of a machine!
The operations of the intellect may furnish us with an illustration.
Ideas are symbols of sensations. The idea of a horse is an abstraction
easily traceable to concrete sensations, yet as an abstraction is
so different a state of feeling that we only identify it with its
concretes by a careful study of its stages of evolution, namely,
sensation, image, reproduced images resembling yet differing from the
original sensation, a coalescence of their resemblances, and finally
the substitution of a verbal symbol for these images. With this symbol
the intellect operates, and sometimes operates so exclusively with it
that not the faintest trace of image or sensation is appreciable--the
word horse takes the place of the image in the sequence of sensorial
processes, just as the image takes the place of the sensation. It does
this as a neural equivalent. In the same way we substitute verbal
symbols for a bag of sovereigns when we pay a creditor with a check;
he pays the check away to another; and this monetary equivalent passes
from hand to hand without a single coin making its appearance. Does
the transaction cease to be commercial, monetary, in this substitution
of signs? No; nor does a process cease to be psychical when an image
is substituted for a sensation, and a verbal symbol for an image. This
every one will admit. Must we not go further, and extend the admission
to automatic actions which originally were voluntary, and have now lost
all trace of ideal prevision, and almost all traces of accompanying
consciousness? _The motor mechanism has its symbols also_; in this
sense, that whereas the action which at first needed complex sensorial
processes to set it going and keep it going, is now determined by a
single one of those processes taking the place of their resultant. When
a practised accountant runs his eye up a column of figures, he does
not pause to realize the values of those figures by decomposing the
symbols into their numerical units, he simply groups one symbol with
another according to their intuited relations, and the final result is
reached with a certainty not less, and a rapidity far greater, than if
it had been reached by step-by-step verification. It is thus with the
pianoforte-player. It is thus with all automatic performances, except
those dependent on the connate adjustments of the mechanism.
CHAPTER VI.
THE PROBLEM STATED.
71. If the preceding attempt to disengage the question from the
ambiguities of its terms has been successful, we shall find little
difficulty in rationally interpreting all the facts adduced in favor
of Animal Automatism, without having recourse to a mechanical theory
of biological phenomena. The objections to that theory are that it
employs terms which have very misleading _connotations_ even when they
do not _denote_ phenomena of widely different orders; so that the moral
repugnance commonly felt at the attempt to treat the animal organism as
if it were a machine, is sustained by the intellectual repugnance at
the attempt to explain biological phenomena on principles derived from
phenomena of a simpler order.
Remark, in passing, this piquant contradiction: the Automaton theory
of Descartes, when applied to the animals, generally excited ridicule
or repulsion; whereas the far more inconsistent and mechanical
theory of Reflex Action has been almost universally welcomed as a
great discovery, though it banishes the Sensibility which Descartes
preserved. And further, the philosophers who most loudly protested
against the idea that animals were machines, were the philosophers
who most insisted that these animals were made, not evolved--planned
by their maker, as a watch is planned by its maker, with a distinct
purpose and prevision in the disposition of every part; whereas the
philosophers who most emphatically reject this notion of organisms
being made, are often those who liken organisms to machines.
72. The paradox propounded by Descartes loses much of its strangeness
when we understand his meaning. Its terms are infelicitous because of
their misleading connotations. When he says that all the actions of
animals which seem to be due to Consciousness are in fact produced on
the same principles as those of a machine, he means that animals have
not souls to direct their actions; but since, on being questioned, he
is ready to admit that animals have sensation, perception, emotion, and
memory, his denial of their souls practically comes to much the same as
the ordinary position that animals have not Thought nor Consciousness
of Self.[220] The admission of sensation is, however, quite enough to
mark the essential difference between an organism and a machine.
73. It was really a great step taken by Descartes when he directed
attention to the fact that all animal actions were executed in
strict conformity with mechanical principles, because both before
his time, and since, we may observe a great disregard of the animal
mechanism, and a disposition to interpret the phenomena on metaphysical
principles. But the connotations of the term “machine” were such as to
lead the mind away from the special conditions of the vital mechanism,
and fix it exclusively on the general conditions of machinery. Hence
his opponents misunderstood him, and some of his followers made the
same oversight, and ended by eliminating sensation altogether. In
pursuance of this mechanical point of view, to the exclusion of the
biological, Thought and even Consciousness have been eliminated from
among the organic agencies, and are said to have no more influence in
determining even human actions than the whistle of the steam-engine has
in directing the locomotive. There are thus two _meta_physiological
theories. According to the one, Consciousness directs indeed the
actions of the organism, but is not itself an organic process--it sits
apart, like a musical performer playing on an instrument. According
to the other, it is not a directing agency, but an accessory product
of certain organic processes, which processes may go on quite as well
without any accompaniment and interference of Consciousness.
74. Two observations arise here. First, we observe a want of due
recognition of the objective and subjective aspects, and their
respective criteria. Secondly, we observe mental facts of irresistible
certainty interpreted by material hypotheses of questionable value;
and not only so, but a higher validity is assigned to the material
hypotheses than to the mental facts they are invented to explain. That
we are conscious, and that our actions are determined by sensations,
emotions, and ideas, are facts which may or may not be explained by
reference to material conditions, but which no material explanation
can render more certain. That animals resemble us in this as in
other respects is an induction of the highest probability. It is
also a fact that many actions take place, as we say, unconsciously
and involuntarily; and that some take place now consciously, now
unconsciously. These facts also we endeavor to explain: and when
we find that some of the unconscious and involuntary actions take
place after the brain has been removed, this is interpreted on the
material hypothesis of the brain being the sole seat of sensation
and consciousness; and is urged in favor of the hypothesis that
consciousness cannot be an agent in the mechanism. Here the confusion
of objective and subjective aspects is patent. Consciousness as a
subjective fact cannot be a material or objective fact. But may it not
be another aspect of that which is objective? So long as we are dealing
with the objective aspect, we have nothing but material processes in a
material mechanism before us. A change within the organism is caused
by a neural stimulation, and the resulting action is a reflex on the
muscles. Here there is simply a transference of motion by a material
mechanism. There is in this no evidence of a subjective agency;
there could be none. But when we come to investigate the process, we
find that it differs from similar processes in anorganisms, by the
necessary co-operation of special conditions, and among these--the
vital conditions--there are those which in their subjective aspect we
express not in terms of Matter and Motion, but in terms of Feeling,
i. e. not in objective but in subjective terms. I see a stone move on
being struck; I also see a man shrink on being struck, and hear a dog
howl on being kicked. I do not infer that the stone feels as the man
and dog feel, because I know the stone and the dog to be differently
constituted, and infer a corresponding difference in their reactions. I
infer that the man and dog feel, because I know they are like myself,
and conclude that what I feel they feel, under like conditions.
75. Descartes says that animals are sensitive automata. They _always_
act as we _sometimes_ act, i. e. when we are not conscious of what we
do, as in singing, walking, playing the piano, etc. We are said to do
these things mechanically, automatically, and hence the conclusion that
these actions are those of a pure mechanism. But it would be truer to
say that we never act mechanically, we always act organically. “When
one who falls from a height throws his hands forwards to save his
head,” says Descartes, “it is in virtue of no ratiocination that he
performs this action” (that depends on the definition: in the Logic
of Feeling there is a process of ratiocination identical with that in
the Logic of Signs). “It does not depend upon his _mind_” (again a
question of definition), “but takes place merely because his senses
being affected by _present danger_” (senses, then, have a perception
of danger?) “some change arises in his brain which determines the
animal spirits to pass thence into the nerves in such a manner as is
required to produce this motion, in the same way as in a machine, and
without his mind being able to hinder it. Now since we observe this in
ourselves, why should we be so much astonished if the light reflected
from the body of a wolf into the eye of a sheep has the same force to
excite in it the motion of flight?”
Here, both in the case of the man and the sheep, there is presupposed
the very mental experience which is denied. The young child will
not throw out its arm to protect itself; but after many experiences
of falling and stumbling, there is an organized perception of the
impending danger, and the means of averting it, and it is this which
determines the throwing out of the arms. If this is not a mental
fact--a process of judgment--then the logical conclusion by which a
financier on hearing a war rumor orders his broker to sell stock, is
not a mental fact. The light reflected from the body of a wolf would
not disturb the sheep unless its own, or its _inherited_ organized
experience were ready there to respond. But this organized experience,
you say, enters into the mechanism? Yes; but it cannot be made to
enter into the mechanism of an automaton, because however complex that
mechanism may be, and however capable of variety of action, it is
constructed solely for definite actions on calculated lines: all its
readjustments must have been foreseen, it is incapable of adjusting
itself to unforeseen circumstances. Hence every interruption in the
prearranged order either throws it out of gear, or brings it to a
standstill. It is regulated, not self-regulating. The organism, on the
contrary--conspicuously so in its more complex forms--is variable,
self-regulating, incalculable. It has _selective adaptation_ (p.
221) responding readily and efficiently to novel and unforeseen
circumstances; _acquiring_ new modes of combination and reaction. An
automaton that will learn by experience, and adapt itself to conditions
not calculated for in its construction, has yet to be made; till it
is made, we must deny that organisms are machines. Automatism in the
organism implies Memory and Perception. A sudden contact--a sudden
noise--a vague form seen in the twilight will excite the mechanism
according to its organized experiences. We start automatically, before
we automatically interpret the cause; we start first, and then ask,
What is that? But we do not always start at sounds or sights which have
no association with previous experiences. The child and the man both
see the falling glass, but the child does not automatically stretch out
a hand to save the glass. Having once learned the action of swimming or
billiard-playing, we automatically execute these; without consciously
remembering the rules, we unconsciously obey them; each feeling as it
rises is linked on to another, each muscle is combined with others in a
remembered synthesis.
76. Kempelen’s chess-player surprised the public, but every instructed
physiologist present knew that in some way or other its movements were
directed by a human mind; simply because no machine could possibly have
responded to the unforeseen fluctuations of the human mind opposed to
it. Even the mind of a dog or a savage would be incompetent to pass
beyond the range of its previous experiences, incompetent to seize the
significance of an adversary’s moves on the chessboard. Now just as
we conclude that mental agency is essential to a game of chess, so we
conclude that Sensibility is essential to the fluctuating responses
of an organism under unforeseen circumstances. We can conceive an
automaton dog that would bark at the presence of a beggar; but not of
an automaton dog that would bark one day at the beggar and the next
day wag his tail, remembering the food and patting that beggar had
bestowed. Since all we know of machines forbids the idea of their
being capable of adjusting their actions to new circumstances, or of
evoking through experience new powers of combination, we conclude that
wherever this capability of adaptation is present there is an agency in
operation which does not belong to the class of mechanical agencies.
Goltz has shown that a frog deprived of its brain manifests so much of
vision as enables it to avoid obstacles--leaping to the right or to
the left of a book placed in its path. This Professor Huxley regards
as purely mechanical:--“Although the frog appears to have no sensation
of light, visible objects act upon the motor mechanism of its body.”
Should we not rather conclude that if the frog had no sensation,
no such effect would follow? because although a machine _might_ be
constructed to respond to variations of light and shadows, none could
be constructed (without Sensibility) to respond to the fluctuating
conditions as an organism responds.[221] Were the reflex actions
of the organism purely mechanical--i. e. involving none of those
fluctuating adjustments which characterize Sensibility--the effect
would be uniform, and proportional to the impact; but it is variable,
and proportional to the static condition of the nervous centres at the
moment. Exaggerate this--by strychnine, for instance--and the slightest
touch on the skin will produce general convulsions. Lower it--by an
anæsthetic--and no reflex at all will follow a stimulus. In anæsthesia
of the mucous membrane, no reflex of the eyelid, no secretion of
tears, follows on the irritation of the membrane; no sneezing follows
irritation of the inside of the nose; no vomiting follows irritation of
the fauces.
77. The question has long ceased to be whether the organism is a
mechanism. To the physiologist it is this before all things. To the
psychologist also it has of late years more and more assumed this
character; because even when he postulates the existence of a spiritual
entity _in_ the organism but not _of_ it, he still recognizes the
necessity of a mechanism for the execution of the acts determined by
the spirit; and when the psychologist adopts the theory of spiritual
phenomena as the subjective aspect of what objectively are material
phenomena, he of course regards the bodily mechanism and the mental
mechanism as one and the same real.
This settled, the problem of Automatism may be thus stated: Granting
the animal organism to be a material mechanism, and all its actions
due to the operation of that mechanism, are we to conclude that it is
an automaton essentially resembling the automata we construct, the
movements of which may, or may not, be _accompanied_ by Feeling, but
are in no case _determined_ by Feeling?
Descartes says that animals are sensitive automata. Professor Huxley
says that both animals and men are sensitive and conscious automata;
so that misleading as the language of Descartes and Professor Huxley
often is in what its terms connote, we do them great injustice if
we suppose them to have overlooked the points of difference between
organisms and machines which have been set forth with so much emphasis
in a preceding chapter; and the reader is requested to understand that
without pretending to say how much the inevitable connotation of their
language expresses their opinions, and how much it may have only led
to their being misunderstood, my criticisms are directed against this
connotation and this interpretation.
CHAPTER VII.
IS FEELING AN AGENT?
78. Descartes having attributed all animal actions to a sensitive
mechanism, and indeed all human actions to a similar mechanism,
endeavored to reconcile this hypothesis with the irresistible facts
of Consciousness--which assured us that _our_ actions, at least, were
determined by Feeling. To this end he assumed that man had a spiritual
principle over and above the sentient principle. The operation of this
principle was, however, limited to Thought; the actions themselves were
all performed by the automatic mechanism; so that, in strict logic, the
conclusion from his premises was the same for man as for animals.
This conclusion Professor Huxley announced in his Address before the
British Association, 1874[222]--to the great scandal of the general
public, which did not understand him aright; and to the scandal also of
a physiological public, which, strangely enough, failed to see that it
was the legitimate expression of one of their favorite theories--the
celebrated Reflex Theory. Now although it is quite open to any one to
reject the premises which lead to such a conclusion, if he sees greater
evidence against the conclusion than for the premises, it is surely
irrational to accept the premises as those of scientific induction,
and yet reject the conclusion because it endangers the stability of
other opinions? For my own part, I do not accept the premises, and my
polemic will have reference to them.
79. Professor Huxley adopts certain Theses which represent the views
generally adopted by physiologists; to which he adds a Thesis which is
adopted by few, and which he only puts forward hypothetically. Against
these positions I place Antitheses, less generally adopted, but which
in my belief approximate more nearly to the inductions of experience.
_Theses._ _Antitheses._
I. There can be no sensation I. There is sensation without
without consciousness. consciousness, if consciousness
means a special mode of Sentience.
II. There can be no II. The co-operation of the brain
consciousness without the is only necessary for a special
co-operation of the brain. mode of Sentience; other modes are
active when the brain is inactive.
III. Sensation and Consciousness III. Unless the molecular changes
are in some inexplicable way be limited to the brain as the
caused by molecular changes in _occasional_ cause, there is
the brain, following upon these no _following_ of sensation or
as one event follows another, motion, no causal link between the
the causal link between motion two; but the neural process _is_
and sensation being a mystery. the sensation, viewed objectively,
the sensation is the neural
process, viewed subjectively. In
this antithesis, Neural Process
is not limited to the brain, but
comprises the whole sensitive
organism as the _efficient_ cause.
IV. All actions which take place IV. All actions are the actions of
unconsciously are reflex, and a reflex mechanism, and all are
reflex actions are the operation sentient, even when unconscious;
of an insentient mechanism; they are therefore never purely
they are therefore as purely mechanical, but always organical.
mechanical as those of automata.
V. The animal body is a reflex V. Sentience being necessary to
mechanism; even when the reflex action, it is necessarily
brain co-operates with the an agent.
other centres, and produces
consciousness, this product is
not an agent in determining
action, it is a collateral
result of the operation.
80. The first four Theses are those current in our textbooks, so
that it is only the fifth which will have the air of a paradox. Nor,
as a paradox, is it without advocates. Schiff long ago suggested it
hypothetically. Hermann mentions it as entertained by physiologists,
whom he does not name.[223] Laycock, and, if I remember rightly, Dr.
Drysdale, have insisted on it; and Mr. Spalding has proclaimed it with
iterated emphasis. Of the Antitheses nothing need be said here, since
the whole of this volume is meant to furnish their evidence.
I have already stated that my polemic is against the views that
Professor Huxley is _supposed_ to hold by those whom his expressions
mislead, rather than against the views I imagine him really to hold.
I have little doubt that he would disavow much that I am forced to
combat, although his language is naturally interpreted in that sense.
But I do not know in how far he would agree with me, and in the
following remarks I shall confine myself to what seems to be the plain
interpretation of his words, since _that_ is the interpretation which
has been generally adopted, and which I most earnestly desire to refute.
81. To begin with this passage. After stating the views of Descartes,
he says: “As actions of a certain degree of complexity are brought
about by mere mechanism, why may not actions of still greater
complexity be the result of a more refined mechanism? What proof is
there that brutes are other than a superior race of marionnettes, which
eat without pleasure, cry without pain, desire nothing, know nothing,
and only simulate intelligence as a bee simulates a mathematician?”
What proof? Why, in the first place, the proof which is implied in
the “more refined mechanism” required for the greater complexity of
actions. In the next place, the proof that the organism of the brute is
very different from the mechanism of a marionnette, and is so much more
like the organism of man, that since we know man to eat with pleasure
and cry with pain, there is a strong presumption that the brute eats
and cries with somewhat similar feelings.
82. Having stated the hypothesis, Professor Huxley says he is not
disposed to accept it, though he thinks it cannot be refuted. His chief
reason for not accepting it is that the law of continuity forbids
the supposition of any complex phenomenon suddenly appearing; the
community between animals and men is too close for us to admit that
Consciousness could appear in man without having its beginnings in
animals. Finding that animals have brains, he justly concludes that
they also must have brain functions; and they also therefore must
be credited with Consciousness. This argument seems to me to have
irresistible cogency; and to be destructive not only of the automaton
hypothesis, but equally of the hypothesis on which the Reflex Theory
is founded. If the law of continuity forbids the sudden appearance of
Consciousness, the law of similarity of property with similarity of
structure forbids the supposition that central nerve-tissue in one
part of the system can suddenly assume a totally different property
in another part. If the brain of an animal, a bird, a reptile, or a
fish--and _a fortiori_ if the œsophageal ganglia of an insect or a
mollusc--may be credited with Sensibility, because of the fundamental
similarity of these structures with the structures of the human brain,
then surely the spinal cord must be credited with Sensibility; for the
tissue of the spinal cord is more like that of the brain, than the
brain of a reptile is like the brain of a man. The sudden disappearance
of all Sensibility, on the removal of one portion of the central
nervous system, would be a violation of the law of continuity. And if
it be said that Consciousness is not the same as Sensibility, but is a
specially evolved function of a specially developed organ, the answer
will be that this is only a difference of mode, and that the existence
of Sensibility is that which renders the automaton and reflex theories
untenable.
83. Professor Huxley would probably admit this; for however his
language may at times seem to point to another conclusion, and is so
far ambiguous, he has expressed the view here maintained with tolerable
distinctness in the following passage, to which particular attention is
called:--
“But though we may see reason to disagree with Descartes’ hypothesis,
that brutes are unconscious machines, it does not follow that he
was wrong in regarding them as automata. _They may be more or less
conscious sensitive automata_; and the view that they are such
conscious machines is that which is implicitly or explicitly adopted
by most persons. When we speak of the actions of the lower animals
being guided by instinct and not by reason, what we really mean is that
though they feel as we do, yet their actions are the results of their
physical organization. We believe, in short, that they are machines,
one part of which (the nervous system) not only sets the rest in motion
and co-ordinates its movements in relation with changes in surrounding
bodies, but is provided with a special apparatus the function of which
is the calling into existence of those states of consciousness which
are termed sensations, emotions, and ideas.”
84. To say that they are “conscious automata” seems granting all that
I demand; but there are two objectionable positions which the phrase
conceals: first, that Consciousness is not a coefficient; and secondly,
that Reflex Action is purely mechanical.
Professor Huxley nowhere, I think, establishes the distinction
between Consciousness as a term for a special mode of Feeling, and
Consciousness as the all-embracing term for sentient phenomena. His
language always implies that an action performed unconsciously is
performed mechanically; which may be acceptable if by unconsciously be
meant insentiently. I hold that whether consciously or unconsciously
performed, the action is equally vital and sentient. In the case he has
cited of a soldier now living who is subject to periodic alternations
of normal and abnormal states, in the latter states all the actions
being said to be “unconscious,” we have only to read the account to
recognize ample evidence of Sentience. Here is a descriptive passage:--
85. “His [the soldier’s in the abnormal state] movements remain free,
and his expression calm, except for a contraction of the brow, an
incessant movement of the eyeballs, and a chewing motion of the jaws.
The eyes are wide open, and their pupils dilated. If the man happens
to be in a place to which he is accustomed he walks about as usual;
but if he is in a new place, or if obstacles are intentionally placed
in his way, he stumbles against them, _stops, and then feeling over
the objects with his hands, passes on one side of them_. He offers
no resistance to any change of direction which may be impressed upon
him, or to the forcible acceleration or retardation of his movements.
He eats, drinks, smokes, walks about, dresses and undresses himself,
rises and goes to bed at the accustomed hours. Nevertheless pins may be
run into his body, or strong electric shocks sent through it, without
causing the least indication of pain; no odorous substance, pleasant or
unpleasant, makes the least impression; he eats and drinks with avidity
whatever is offered, and takes asafœtida or vinegar of quinine as
readily as water; no noise affects him; and light influences him only
under certain conditions.”
There is no one of these phenomena that is unfamiliar to students of
mental disease. The case is chiefly remarkable from the periodicity of
the recurrence of the abnormal state. I have collected other cases of
the kind, and may hereafter find a fitting occasion to quote them.[224]
The anæsthesia and “unconsciousness” noted, no more prove the actions
performed by this soldier to have been purely mechanical, i. e.
undetermined by sensation, than anæsthesia and unconsciousness prove
somnambulists and madmen to be machines. In the pathological state
called “ecstasy” there is a considerable diminution of sensibility to
external stimuli; with a concentration on certain feelings, images,
trains of thought, exhibiting itself in expressions of emotion.
“Les malades,” says a master, “paraissent entièrement absorbés par
leurs mouvements intérieurs, ils refusent généralement de manger, et
spécialement la volonté de l’âme semble complètement enchainée.”[225]
86. Observe that while this soldier exhibits such insensibility to
certain stimuli, he unequivocally exhibits sensibility to other
stimuli. All his acts show sense-guidance. Sight and Touch obviously
regulate his movements. And when he feels objects placed in his way,
and then passes beside them, wherein does this differ from the normal
procedure of sensitive organisms? wherein does it resemble automata?
Dr. Mesmet--from whose narrative the case is cited--remarks that the
sense of Touch seems to persist “and indeed to be more acute and
delicate than in the normal state”; upon which Professor Huxley has
this comment:--“Here a difficulty arises. It is clear from the facts
detailed that the nervous apparatus by which in the normal state
sensations of touch are excited is that by which external influences
determine the movements of the body in the abnormal state. But does the
state of consciousness, which we term a tactile sensation, accompany
the operation of this nervous apparatus in the abnormal state? or
is consciousness utterly absent, the man being reduced to a pure
mechanism? It is impossible to obtain direct evidence in favor of the
one conclusion or the other; all that can be said is that the case of
the frog shows that the man may be devoid of any kind of consciousness.”
87. It is here we are made vividly aware of the absolute need there is
to disengage the terms employed from their common ambiguities. All the
evidence of a tactile sensation which can possibly be furnished, on the
objective side, is furnished by the actions of this soldier; to doubt
it would be to throw a doubt on the sensibility of any animal unable
to _tell_ us what it felt; nay, even a man if he were dumb, or spoke
a language we could not understand, could give us no other proof. We
conclude that the soldier had tactile sensations, because we see him
guided by them as we ourselves are guided by tactile sensations; we
know that he is an organism, not a machine, and therefore reject the
inference that he has become reduced to a “pure mechanism” because
it is inferred that his consciousness is absent. And on what is this
inference grounded? 1°, The belief that the brain is the sole organ
of consciousness (Sentience)--a belief flatly disproved by the facts,
which show Sentience when the brain has been removed; and 2°, the
belief that the decapitated frog, because it avoids obstacles and
redirects its leaps to avoid them, does so without Sentience. According
to the definition we adopt, we may either say that the decapitated
frog, and the soldier in his abnormal state, act without consciousness,
or with it. But what does not seem permissible is to deny that their
actions exhibit the clearest evidence of _sense-guidance_, and the
kind of volition which this sense-guidance implies; and this is quite
enough to separate them from actions of automata. When a man ducks his
head to avoid a stone which he sees falling towards him, he assuredly
has a sensation, i. e. there is a grouping of neural elements, which
subjectively is a sensation, and this originates a grouping of other
neural elements, the outcome of which is a muscular movement, which
subjectively is a motor sensation: _this_ grouping would not have
been originated unless the particular grouping had preceded it; nor
would the simple retinal stimulus have excited this sensation unless
the nerve-centres had been attuned to such response by many previous
experiences: the ignorant child would not duck its head on seeing
the stone approach. In our familiar use of the word Consciousness it
would be correct to say that the man ducks his head “unconsciously”;
and yet expressing the fact in psychological language, we also say:
He ducks his head because _remembering_ the pain of former similar
experiences, he _knows_ that if the stone strikes him he will again
be hurt as before, therefore he _wills_ to avoid it; expressing it
in physiological language we may say: The man acts thus because he
is so organized that a particular neural process is the stimulus of
a particular central discharge; and he became thus organized through
a long series of anterior adjustments responding to stimuli, each
adjustment being the activity of the vital organism.
88. There can be no doubt that the soldier had perceptions, and that
these perceptions guided his movements; whether these shall be called
“states of consciousness” or not, is a question of terms. Now since
we know that _certain actions are uniformly consequent on certain
perceptions_, we are justified in inferring that _whenever the
actions are performed, the perceptions preceded them_: this inference
may be erroneous, but in the absence of positive evidence to the
contrary it is that which claims our first assent. Is it evidence to
the contrary that the perception may have stimulated the action, yet
been unaccompanied by the special mode named consciousness? Not in
the least. We learn to read with conscious effort; each letter has
to be apprehended separately, its form distinguished from all other
forms, its value as a sign definitely fixed, yet how very rarely are
we “conscious” of the letters when we read a book? Each letter is
perceived; and yet this process passes so rapidly and smoothly, that
unless there be some defect in a letter, or the word be misspelled,
we are not “conscious” of the perceptions. Are we therefore reading
automata?[226]
We are said to walk unconsciously at times; and the continuance of the
movement is said to be due to reflex action. But it is demonstrable
that the cutaneous sensibility of the soles of the feet is a primary
condition. If the skin be insensible, the walking becomes a stumble. In
learning to walk, or dance, the child fixes his eyes on his feet, as he
fixes them on his fingers in learning to play the piano. After a while
these registered sensations _connected_ with the muscular sense suffice
to guide his feet or his fingers; but not if feet or fingers lose their
sensibility.
89. With these explanations let us follow the further details of this
soldier’s abnormal actions:--
“The man is insensible to sensory impressions made through the ear,
the nose, the tongue, and, to a great extent, the eye; nor is he
susceptible to pain from causes operating during his abnormal state.
Nevertheless it is possible _so to act upon his tactile apparatus as
to give rise to those molecular changes in his sensorium which are
ordinarily the causes of associated trains of ideas_. I give a striking
example of this process in Dr. Mesmet’s words: ‘Il se promenait dans
le jardin, on lui remet sa canne qu’il avait laissé tomber. Il la
palpe, promène à plusieurs reprises la main sur la poignée coudée de
sa canne--devient attentif--semble prêter l’oreille--et tout à coup
appelle, “Henri! les voilà!” Et alors portant la main derrière son
dos comme pour prendre une cartouche, il fait le mouvement de charger
son arme, se couche dans l’herbe à plat ventre dans la position d’un
tirailleur, et suit avec l’arme épaulée tous les mouvements de l’ennemi
qu’il croit voir à courte distance.’ In a subsequent abnormal period
Dr. Mesmet caused the patient to repeat this scene by placing him in
the same conditions. Now in this case the question arises whether the
series of actions constituting this singular pantomime was accompanied
by the ordinary states of consciousness, the appropriate trains of
ideas, or not? Did the man dream that he was skirmishing? or was he in
the condition of one of Vaucanson’s automata--_a mechanism worked by
molecular changes in the nervous system_? The analogy of the frog shows
that the latter assumption is perfectly justifiable.”
90. Before criticising this conclusion let me adduce other
illustrations of this dreamlike activity. “A gentleman whom I attended
in a state of perfect apoplexy,” says Abercrombie, “was frequently
observed to adjust his nightcap with the utmost care when it got into
an uncomfortable state: first pulling it down over his eyes, and
then turning up the front of it in the most exact manner.” According
to the current teaching, these actions, which seem like evidence
of sensation, are nothing of the kind, because--the patient was
“unconscious”; that is to say, because he did not exhibit one complex
kind of Sensibility, it is denied that he exhibited another kind!
he did not feel discomfort, nor feel the movements by which it was
rectified--because he could not speak, discuss impersonal questions,
nor attend to what was said to him! Abercrombie cites other cases: “A
gentleman who was lying in a _state of perfect insensibility_ from
disease of the brain” (note the phrase, which really only expresses
the fact that external stimuli did not create their normal reactions)
“was frequently observed even the day before his death to take down
a repeating watch from a little bag at the head of his bed, put it
close to his ear and make it strike the hour, and then replace it in
the bag with the greatest precision. Another whom I saw in a state of
profound apoplexy, from which he recovered, had a perfect recollection
of what took place during the attack, and mentioned many things which
had been said in his hearing when he was supposed to be in a state of
perfect unconsciousness.” Dr. Wigan also tells of a lady whom he knew,
and who was actually put in a coffin, under the belief that she was
dead when in a trance. Her sense of hearing was then preternaturally
acute. In her second-floor bedroom she heard what the servants said
in her kitchen. When her brother came to see her and he declared she
should not be buried until putrefaction set in, she felt intense
gratitude and a gush of tenderness, but was unable to move even an
eyelid as a manifestation of her feeling. Suddenly all her faculties
returned. Dr. Wigan adds that he visited the Countess Escalante, one
of the Spanish refugees, who remained in a similar state for a short
period, during which she saw her husband and children, and was quite
conscious of all they did and said--but did not recognize them as her
own. She was absolutely without the power of moving a finger or of
opening her mouth. Dr. Neil Arnott told me of a similar case in his
practice. In these last cases we learn that consciousness--in its
ordinary acceptation--was present, though bystanders could see no trace
of it. And very often in cases where Consciousness, or at any rate
Sensibility, is clearly manifested, its presence is denied, because the
patient on recovering his normal condition is quite unable to remember
anything that he felt and did. Under anæsthetics patients manifest
sensation, but on awaking they declare that they felt nothing--of
what value is their declaration? M. Despine tells us of a patient who
under chloroform struggled, swore, and cried out, “_Mon Dieu! que
je souffre!_” yet when the operation was over, and he emerged from
the effects of the chloroform, he remembered nothing of what he had
felt.[227]
91. Returning now to Dr. Mesmet’s soldier, and to the conclusion that
his dreamlike acts were no more than the actions of one of Vaucanson’s
automata, surely we are justified in concluding, first, that these
actions were not of the same kind as those of an automaton, since they
were those of a living organism; secondly, that they present all the
evidence positive and inferential which Sensibility can present in
the actions we observe in another, and do not feel in ourselves; and
thirdly, if with physiologists we agree that the mechanism of these
actions is “worked by molecular changes in the nervous system,” there
is some difficulty in understanding how Consciousness, which is said
to be caused by such changes, could have been absent--how the _cause
could operate yet no effect be produced_.
92. What automata can be made to perform is surprising enough, but
they can _never_ be made to display the fluctuations of sense-guided
actions, such as we see in the report of Dr. Mesmet’s soldier:--
“The ex-sergeant has a good voice, and had at one time been employed
as a singer at a café. In one of his abnormal states he was observed
to begin humming a tune. He then went to his room, dressed himself
carefully, and took up some parts of a periodical novel which lay
on the bed, as _if he were trying to find something_. Dr. Mesmet,
suspecting that he was seeking his music, made up one of these into a
roll and put it into his hand. _He appeared_ satisfied, took up his
cane, and went down stairs to the door. Here Dr. Mesmet turned him
round, and he walked quite contentedly in the opposite direction. The
_light of the sun_ shining through a window happened to fall upon
him, and _seemed to suggest the footlights of the stage_ on which he
was accustomed to make his appearance. He stopped, opened his roll of
imaginary music, put himself in the attitude of a singer, and sang with
perfect execution three songs one after the other. After which he wiped
his face with his handkerchief and drank without a grimace a tumbler of
strong vinegar-and-water.”
93. Epileptic patients have frequently been observed going through
similar dreamlike actions in which only those external stimuli which
have a relation to the dream seem to take effect.[228] We interpret
these as phenomena of _disordered_ mental action, the burden of proof
lies on him who says they are phenomena of pure mechanism. A mail-coach
does not suddenly cease to be a mail-coach and become a wheelbarrow
because the coachman is drunk, or has fallen from the box. The horses,
no longer guided by the reins, may dash off the highroad into gardens
or ditches; but it is their muscular exertions which still move the
coach.
Can any one conceive an automaton acting as the sergeant is described
to be in the following passage?--
“Sitting at a table he took up a pen, felt for paper and ink, and began
to write a letter to his general, in which he _recommended himself for
a medal_ on account of his good conduct and courage. It occurred to
Dr. Mesmet to ascertain experimentally how far vision was concerned in
this act of writing. He therefore interposed a screen between the man’s
eyes and his hands; under these circumstances he _went on writing for
a short time, but the words became illegible, and he finally stopped_.
On the withdrawal of the screen, he _began to write again where he had
left off_. The substitution of water for ink in the inkstand had a
similar result. He stopped, _looked at his pen, wiped it on his coat_,
dipped it in the water, and began again, with the same effect. On one
occasion he began to write upon the topmost of ten superposed sheets
of paper. After he had written a line or two, this sheet was suddenly
drawn away. _There was a slight expression of surprise_, but he
continued his letter on the second sheet exactly as if it had been the
first. This operation was repeated five times, so that the fifth sheet
contained nothing but the writer’s signature at the bottom of the page.
Nevertheless, when the signature was finished, his eyes turned to the
top of the blank sheet, and he went through the form of reading over
what he had written, a movement of the lips accompanying each word;
moreover, with his pen _he put in such corrections as were needed_.”
94. Dr. Mesmet concludes that “his patient sees some things and not
others; that the sense of sight is accessible to all things which
are brought into relation with him by the sense of touch, and, on the
contrary, is insensible to things which lie outside this relation.”
In other words, the sensitive mechanism acts, but acts abnormally.
This is precisely what is observed in somnambulists. Yet Professor
Huxley, who makes the comparison, appears to regard both states as
those in which the organism is reduced to a mere mechanism, because
on recovering their normal state the patients are unconscious of what
has passed; and because the frog, without its brain, also manifests
analogous phenomena. Neither premise warrants the conclusion. I
have already touched on the unconsciousness of past actions; let me
add the case of Faraday, who was assuredly not an automaton when he
prepared and delivered a course of lectures which were nevertheless so
entirely obliterated from his memory that the next year he prepared and
delivered the same course once more, without a suspicion that it was
not a new one. As to the frog, I must leave that case till I come to
examine the evidence on which the hypothesis of the purely mechanical
nature of spinal action rests.
95. The point never to be left out of sight is that actions which are
known to be preceded and accompanied by sensations do not lose their
special character of Sentience, as actions of a sentient mechanism,
because they are not also preceded and accompanied by that peculiar
state which is specially called Consciousness, i. e. attention to the
passing changes (comp. p. 403). When we see a man playing the piano,
and at the same time talking of something far removed from the music,
we say his fingers move unconsciously; but we do not conclude that
he is a musical machine--muscular sensations and musical sensations
regulate every movement of his fingers; and if he strikes a false
note, or if one of the notes jangles, he is instantly conscious of
the fact. Either we must admit that his brain is an essential part
of the mechanism by which the piano was played, and its function an
essential agent in the playing; or else we must admit that the brain
and its function were not essential, and therefore the playing would
continue if the brain were removed. In the latter case, we should have
a musical automaton. That a particular group of sensations, such as
musical tones, will set going a particular group of muscular movements,
without the intervention of any _conscious_ effort, is not more to be
interpreted on purely mechanical principles, than that a particular
phrase will cause a story-teller to repeat a familiar anecdote, or an
old soldier “to fight his battles o’er again.”
96. Let us now pass to another consideration, namely, whether
Consciousness--however interpreted--is legitimately conceived as a
factor in the so-called conscious and voluntary actions; or is merely a
_collateral result_ of certain organic activities? To answer this, we
must first remember that Consciousness is a purely subjective process;
although we may believe it to be objectively a neural process, we are
nevertheless passing out of the region of Physiology when we speak of
Feeling determining Action. Motion may determine Motion; but Feeling
can only determine Feeling. Yet we do so speak, and are justified. For
thereby we implicitly declare, what Psychology explicitly teaches,
namely, that these two widely different aspects, objective and
subjective, are but the two faces of one and the same reality. It
is thus indifferent whether we say a sensation is a neural process,
or a mental process: a molecular change in the nervous system, or a
change in Feeling. It is either, and it is both, as I have elsewhere
explained.[229] There it was argued that the current hypothesis of a
neural process _causing_ the mental process--molecular movement being
in some mysterious way _transformed_ into sensation--is not only
inconceivable, but altogether unnecessary; whereas the hypothesis
that the two aspects of the one phenomenon are simply two different
expressions, now in terms of Matter and Motion, and now in terms of
Consciousness, is in harmony with all the inductive evidence.
97. “It may be assumed,” says Professor Huxley, “that molecular
changes in the brain are the causes of all the states of consciousness
of brutes. Is there any evidence that these states of consciousness
may conversely cause those molecular changes which give rise to
muscular motion? I see no such evidence. The frog walks, hops, swims,
and goes through his gymnastic performances, quite as well without
consciousness, and consequently without volition, as with it; and if a
frog in his natural state possesses anything corresponding with what
we call volition, there is no reason to think that _it is anything but
a concomitant of the molecular changes in the brain_, which _form part
of the series involved in the production of motion_. The consciousness
of brutes would appear to be related to the mechanism of their body
simply as a collateral product of its working, and to be _as completely
without any power of modifying that working as the steam-whistle which
accompanies the work of a locomotive engine is without influence
upon its machinery_. Their volition, if they have any, is an emotion
_indicative_ of physical changes, not a _cause_ of such changes.”
Particular attention is called to the passages in italics. In the first
is expressed a view which seems not unlike the one I am advocating, but
which is contradicted by the second. Let us consider what is implied.
98. When Consciousness is regarded solely under its subjective aspect
there is obviously no place for it among material agencies, regarded
as objective. So long as we have the material mechanism in view we
have nothing but material changes. This applies to the frog, with
or without its brain; to man, supposed to be moved by volition, or
supposed to move automatically. The introduction of Consciousness is
not the introduction of another agent in the series, but of a new
aspect; the neural process drops out of sight, the mental process
replaces it. The question whether we have any ground for inferring
that in the series there is included the particular neural state which
subjectively is a state of Consciousness, must be answered according
to the evidence. Well, the evidence shows that the actions do involve
the co-operation; and this Professor Huxley expresses when he says that
the molecular changes in the brain form part of the series involved in
the production of motion. Whether we regard the process objectively
as a series of molecular changes, or subjectively as a succession of
sentient changes, the sum of which is on the one side a motor impulse,
on the other a state of consciousness, we must declare Consciousness
to be an agent, _in the same sense that we declare one change in the
organism to be an agent in some other change_. The facts are the same,
whether we express them in physiological or in psychological terms. The
physiologist, having only the material aspect of the organism in view,
says, “A cerebral process initiates a motor process”; the psychologist
says, “A sensation determines an action.” Unless the two processes have
been linked together by an organic disposition, native or acquired,
there will be no such motor process following the cerebral process.
A dog standing outside the gate is unable to ring the bell, though
having seen another dog ring it, he may wish to do so; but the cerebral
process (his wish) is not linked on to the needful motor process--he
has not learned to realize the wish; whereas the other dog, having by
trial hit upon the right mode of directing his muscles, has registered
this experience, and can ring the bell. The organized disposition
which enables the dog to do this may truly enough be called a
modification of the mechanism; but what we have here to note is that a
sensation originally determined the movement, and always determines it.
99. It is the unfortunate ambiguity of the word Consciousness, and
the questionable hypothesis of the brain being the sole seat of
Sensibility, which darken this investigation. Because animals, after
the brain has been removed, are seen to perform certain actions
as deftly as before, they are said to perform these without the
intervention of Consciousness; when all that is proved by the facts is
that these actions are performed without the intervention of the brain.
In support of this explanation, examples are cited of unconscious
actions performed by human beings. But if we assign Sensibility not to
one part of the nervous system exclusively, but to the whole, we can
readily understand how the loss of a part will be manifested by very
marked changes in the reactions of the whole, and yet not altogether
prevent the reactions of the parts remaining intact. An animal must
respond somewhat differently with and without a brain. One marked
difference is the spontaneity of the actions when the brain is intact,
and the loss of much spontaneity when the brain is injured or removed.
Cerebral processes prompt and regulate actions, as the pressure of the
driver on the reins prompts and regulates the movements of the horses;
but the carriage is moved by the horses and not by the driver; and the
action is executed by the motor mechanism, whether the incitation arise
in a cerebral process or a peripheral stimulation.
100. If we admit that Consciousness is itself an organic process,
accompanying the molecular changes as a convex surface accompanies
a concave, we must also admit that its fluctuations are adjustments
and readjustments of the organic mechanism, and that the actions are
the effects of these--their resultants. The loss of the brain must
obviously cause a great disturbance in these adjustments. We may call
that a loss of Consciousness, if we choose to limit the term to one
_mode_ of sentient reaction. But this loss of a mode does not change
those reactions which persist so as to convert them into purely
mechanical reactions. A troop of soldiers may have lost its directing
officer, but will fight with the old weapons and the old intelligence,
though not with the same convergence of individual efforts. A frog or a
pigeon no more acts as _well_ without a brain as with a brain, than the
troop of soldiers fights as well without an officer.
101. Having thus claimed a place for Consciousness in the series of
organic processes, let us now see whether it has a place among the
active agencies. According to Professor Huxley it is not itself an
agent, but only the “collateral product of the working of the machine.”
It accompanies actions, it does not direct them. It is an index, not a
cause.
Surely it seems more accurate to say that it accompanies _and_ directs
the working? It accompanies the working in two senses: first, as the
subjective aspect of the objective process; secondly, as the change
which produces a subsequent change, that is to say, the movements
initiated by a feeling are themselves also _felt as they pass_; and
this feeling enters into the general stream of simultaneous excitations
out of which new movements and feelings arise; or to express it
physiologically, the sensory impressions determine muscular movements,
which in turn react on the nerve-centres, and these reactions
blend with the general excitation of reflected and re-reflected
processes.[230] Since every change in Consciousness is a change in
the sentient organism, which objectively is a change in the nervous
centres, the working of the mechanism being itself a dependent series
of such changes, each movement must have a reflected influence on the
general state. This reflected influence may be viewed as a collateral
product of the working; but there is no real analogy between it and
the whistle of the steam-engine, because this reflected influence
demonstrably _does_ intervene in the _subsequent_ movements. The
feeling which accompanies or follows a particular movement cannot
indeed modify _that_ movement, since that is already set going, or
has passed; here there is some analogy to the steam-whistle; but the
analogy fails in the subsequent history: no movements whatever of
the steam-engine are modified by the whistle which accompanies the
working of that engine; yet how the reflected influence modifies the
working of the organism! If the hand be passing over a surface, there
is, accompanying this movement, a succession of muscular and tactile
feelings which may be said to be collateral products. But the feeling
which _accompanies_ one muscular contraction _is itself the stimulus_
of the next contraction; if anywhere during the passage the hand
comes upon a spot on the surface which is wet or rough, the change in
feeling thus produced, although a collateral product of the movement,
instantly changes the direction of the hand, suspends or alters the
course--that is to say, the _collateral product of one movement becomes
a directing factor in the succeeding movement_. Now this is precisely
what no automaton can effect, unless for changes that are prearranged.
A steam-engine drives its locomotive over the rails, be they smooth
or rough, entire or broken; it whistles as it goes, but no whistling
directs and redirects its path.
102. Volition is said to be an “emotion indicative of physical changes,
not a cause of such changes.” Here it is necessary to understand in
what sense the term cause is employed. I should prefer stating the
proposition thus: a volition is a state of the sentient organism,
indicative of physical changes which have taken place, and of changes
which will take place. Because it is the _expression_ of the first
group of changes, it cannot be their _origin_; but it can be, and is
the origin of the second group, which it initiates. The indignation
excited by an insult or a blow is not the origin of the emotion or
the pain, but it is the origin of the actions which are prompted by
this sentient state. In fact no sooner do we admit that the organism
is a sentient mechanism, than the conclusion is irresistible that
Sensibility is a factor in the working of that mechanism.
103. “Much ingenious argument,” says Professor Huxley, “has at various
times been bestowed upon the question: How is it possible to imagine
that volition which is a state of consciousness, and as such has not
the slightest community of nature with matter and motion, can act upon
the moving matter of which the body is composed, as it is assumed to do
in voluntary acts? But if, as is here suggested, the voluntary acts of
brutes--or in other words, the acts which they desire to perform--are
as purely mechanical as the rest of their actions, and are simply
accompanied by the state of consciousness called volition, the inquiry,
so far as they are concerned, becomes superfluous. Their volitions
do not enter into the chain of causation of their actions at all....
As consciousness is brought into existence only as the consequence
of molecular motion in the brain, it follows that it is an indirect
product of material changes. The soul stands related to the body as the
bell of a clock to the works, and consciousness answers to the sound
which the bell gives out when it is struck.” This has been answered in
the foregoing pages; nor do I think the reader who has recognized the
ambiguity of the term Consciousness, and the desirability of replacing
it in this discussion by the less equivocal term Sentience, will need
more to be said.
104. The important question whether reflex actions are insentient, and
therefore mechanical, will occupy us in the next problem. The question
of Automatism which has been argued in the preceding chapters, may,
I think, be summarily disposed of by a reference to the irresistible
evidence each man carries in his own consciousness that his actions
are frequently--even if not always--determined by feelings. He is
quite certain that he is not an automaton, and that his feelings are
not simply collateral products of his actions, without the power of
modifying and originating them. Now this fundamental fact cannot be
displaced by any theoretical explanation of its factors. Nor would
this fundamental truth be rendered doubtful, even supposing we were to
grant to the full all that is adduced as evidence that _some_ actions
were the result of purely mechanical processes without sentience at
all. I am a conscious organism, even if it be true that I sometimes act
unconsciously. I am not a machine, even if it be true that I sometimes
act mechanically.
PROBLEM IV.
THE REFLEX THEORY.
“Si omnes patres sic, et Ego non sic.”--ABELARD, _Sic et Non_.
“Will man bestimmen wo der Mechanismus aufhört und wo der Wille
anfängt so ist die Frage überhaupt falsch gestellt. Denn man setzt
hier Begriffe einander gegenüber die gar keine Gegensätze sind.
Vorgebildet in den mechanischen Bedingungen des Nervensystems sind
_alle_ Bewegungen.”--WUNDT, _Physiologische Psychologie_.
“Sollte die so durchsichtige Homologie zwischen Hirn and
Rückenmark, wie solche sich schlagend in Bau und Entwicklung
darthut, wesentlich andere physiologische Qualitäten
bedingen?”--LUSCHINGER in _Pflüger’s Archiv_, Bd. XIV. 384.
THE REFLEX THEORY.
CHAPTER I.
THE PROBLEM STATED.
1. The peculiarity of the Reflex Theory is its exclusion of Sensibility
from the actions classed as reflex; in consequence of which, the
actions are considered to be “purely mechanical.”
No one denies that most of the reflex actions often have conscious
sensations preceding and accompanying them, but these are said not
to be essential to the performance of the actions, because they may
be absent and the actions still take place. It is notorious that we
breathe, wink, swallow, etc., whether we are conscious of these actions
or not. Our conclusion therefore is that these peculiar states of
Consciousness are _accessory_, not essential to the performance of
these actions. The fact is patent, the conclusion irresistible. But
now consider the equivoque: because an action takes place without our
being conscious of it, the action is said to have had no sensation
determining it. This, which is a truism when we limit Consciousness to
one of the special modes Of Sensibility, or limit sensation to this
limited Consciousness, is a falsism when we accept Consciousness as
the total of all combined sensibilities, or Sensation as the reaction
of the sensory mechanism. That a reflex action is determined by the
sensory mechanism, no one disputes; whether the reaction of a sensory
mechanism shall be called a sensation or not, is a question of terms.
I have shown why it must be so called if anything like coherence is to
be preserved in physiological investigations; and I have more than once
suggested that the fact of intellectual processes taking place at times
with no more consciousness than reflex actions, is itself sufficient to
show that a process does not lapse from the mental to the mechanical
sphere simply by passing unconsciously.
Inasmuch as an organism is a complex of organs, its total function must
be a complex of particular functions, each of which may analytically
be treated apart. Vitality is the total of all its physiological
functions, and Consciousness the total of all its psychological
functions. But inasmuch as it is only in its relation to the whole that
each part has functional significance, and cannot therefore be isolated
in reality, as it is in theory--cannot live by itself, act by itself,
independently of the organism of which it is an organ, there is strict
accuracy in saying that no particular sensation can exist without
involving Consciousness; for this is only saying that no sensory organ
can react without at the same time involving a reaction of the general
sensorium. But since this general sensorium is simultaneously affected
by various excitations each of which is a force, every sensation,
perception, emotion, or volition is a _resultant_ of the composition
of these forces; and as there can be only one resultant at a time, to
be replaced by another in swift succession, this one represents the
_state_ of Consciousness, and this state may or may not be felt under
the peculiar _mode_ named “Consciousness,” in its special meaning. In
other words, the reaction of a sensory organ is always sentient, but
not always consentient.
2. Let us illustrate this by the sensation of musical tone. When
we hear a tone we are affected not only by the fundamental tone,
representing the vibrations of the sounding body as a whole, but
also by the harmonics or overtones, representing the vibrations of
the several parts of that whole. It is these latter vibrations which
give the tone its timbre, or peculiar _quality_; and as the harmonics
are variable with the variable structure of the vibrating parts, two
bodies which have the same fundamental tone may have markedly different
qualities. There are some tones which are almost entirely free from
harmonics; that is to say, their harmonics are too faint for our ear to
appreciate them, though we know that the vibrations must be present.
Apply this to the excitations of the sensorium. Each excitation will
have its fundamental feeling, and more or less accompanying thrills of
other feelings: it is these thrills which are the harmonics, giving to
each excitation its specific quality; but they may be so faint that no
specific quality is discriminated. A fly settles on your hand while you
are writing, the faint thrill which accompanies this excitation of your
sensory nerve gives the specific sensation of tickling, and this causes
you to move your hand with a jerk. If your attention is preoccupied,
you are said to be unconscious of the sensation, and the jerk of
your hand is called a reflex action; but if your attention is not
preoccupied, or if the thrill is vivid, you are said to be conscious
of the sensation, and the action is no longer reflex, but volitional.
Obviously here the difference depends not on the sentient excitation by
an impression on the nerve, but on the state of the general sensorium
and its consequent reaction. Had not the impression been carried to the
sensorium, no movement would have followed the fly’s alighting on your
hand, because no sensation (sensory reaction) would have been excited;
the hypothesis of a purely mechanical reflex is quite inadmissible.
3. Or take another case. It sometimes happens that we fall asleep
while some one is reading to us aloud. The sounds of the reader’s
voice at first awaken the familiar thrills which give the tones their
quality, and the words their significance; but gradually as sleep
steals over us, the organism ceases to react thus; the words lose more
and more of their significance, the tones lose more and more of their
harmonics; at last we pass into the state of unconsciousness--we cease
to hear what is read. But do we cease to feel? We have not _heard_,
but we have been _affected_ by the sounds. Not by distinguishable
sensations; nevertheless a state of the general Sensibility has been
induced. To prove that we have been affected is easy. Let the reader
suddenly cease, and if our sleep be not too profound, we at once awake.
Now, unless the sound of his voice had affected us, it is clear that
the cessation of that could not have affected us. Or let us suppose
our sleep to be unbroken by the cessation of the sound; even this will
not prove that we have been unaffected by the sounds, it will merely
prove that those sounds, or their cessation, did not excite a conscious
state. For let the reader, in no louder tone, ask, “Are you asleep?”
and we start up, with round eyes, declaring, “Not at all.” Nay, should
even this question fail to awaken us, the speaker need only utter some
phrase likely to excite a thrill--such as, “There’s the postman!” or,
“I smell fire!” and we start up.
I remember once trying the experiment on a wearied waiter, who had
fallen asleep in one of the unoccupied boxes of a tavern. His arm
rested on the table, and his head rested on his arm: he snored the
snore of the weary, in spite of the noisy laughter and talk of the
guests. I called out “Johnson,” in a loud tone. It never moved him. I
then called “Wilson,” but he snored on. No sooner did I call “waiter,”
than he raised his head with a sleepy “_yessir_.” Now, to suppose, in
this case, that he had _no_ sensation when the words “Johnson” and
“Wilson” reached his ears, but had a sensation when the word “waiter”
reached his ears, is to suppose that two similar causes will not
produce a similar effect. The dissyllable “Johnson” would excite as
potent a reaction of his sensory organ as the dissyllable “waiter”;
but the thrills--the reflex feelings--were different, because the word
“Johnson” was not associated in his mind with any definite actions,
whereas the word “waiter” was so associated as to become an automatic
impulse.[231]
4. Two sisters are asleep in the same bed, and a child cries in the
next room. The sounds of these cries will give a similar stimulus
to the auditory nerve of each sister, and excite a similar sensory
reaction in each. Nevertheless, the one sister sleeps on undisturbed,
and is said not to hear the cry. The other springs out of bed, and
attends to the child, because she being accustomed to attend on the
child and soothe it when crying, the primary sensation has excited
secondary sensations, thrills which lead to accustomed actions. Could
we look into the mind of the sleeping sister, we should doubtless find
that the sensation excited by the child’s cry had merged itself in
the general stream, and perhaps modified her dreams. Let her become a
mother, or take on the tender duties of a mother, and her vigilance
will equal that of her sister; because the cry will _then_ excite a
definite reflex feeling, and a definite course of action. But this very
sister, who is so sensitive to the cry of a child, will be undisturbed
by a much louder noise; a dog may bark, or a heavy wagon thunder along
the street, without causing her to turn in bed.[232]
Although during sleep the nervous centres have by no means their
full activity, they are always capable of responding to a stimulus,
and sensation will always be produced. When the servant taps at your
bedroom door in the morning, you are said not to hear the tap, if
asleep; you do not perceive it; but the sound reaches and rouses you
nevertheless, since when the second tap comes, although no louder, you
distinctly recognize it. In etherized patients, sensation is constantly
observed returning before any consciousness of what is going on
returns. “I was called,” says Mr. Potter, “to give chloroform to a lady
for the extraction of ten teeth. The first five were extracted without
the slightest movement, but as the operation proceeded, sensation
returned, and I was obliged to use considerable force to keep her in
the chair during the extraction of the last tooth. She came to herself
very shortly after, and was delighted to find she had got over all her
troubles without having felt it the least in the world.”[233]
5. We do not see the stars at noonday, yet they shine. We do not see
the sunbeams playing among the leaves on a cloudy day, yet it is by
these beams that the leaves and all other objects are visible. There
is a general illumination from the sun and stars, but of this we are
seldom aware, because our attention falls upon the illumined objects,
brighter or darker than this general tone. There is a sort of analogy
to this in the general Consciousness, which is composed of the sum of
sensations excited by the incessant simultaneous action of internal
and external stimuli. This forms, as it were, the daylight of our
existence. We do not habitually attend to it, because attention falls
on those particular sensations of pleasure or of pain, of greater
or of less intensity, which usurp a prominence among the objects of
the sensitive panorama. But just as we need the daylight to see
the brilliant and the sombre forms of things, we need this living
Consciousness to feel the pleasures and the pains of life. It is
therefore as erroneous to imagine that we have no other sensations than
those which we distinctly recognize--as to imagine that we see no other
light than what is reflected from the shops and equipages, the colors
and splendors which arrest the eye.
The amount of light received from the stars may be small, but it is
present. The greater glory of the sunlight may render this starlight
inappreciable, but it does not render it inoperative. In like manner
the amount of sensation received from some of the centres may be
inappreciable in the presence of more massive influences from other
centres; but though inappreciable it cannot be inoperative--it must
form an integer in the sum.
6. The reader’s daily experience will assure him that over and above
all the particular sensations capable of being separately recognized,
there is a general stream of Sensation which constitutes his feeling
of existence--the Consciousness of himself as a sensitive being. The
ebullient energy which one day exalts life, and the mournful depression
which the next day renders life a burden almost intolerable, are
feelings not referable to any of the particular sensations, but arise
from the massive yet obscure sensibilities of the viscera, which form
so important a part of the general stream of Sensation. Some of these
may emerge into distinct recognition. We may feel the heart beat, the
intestines move, the glands secrete; anything _unusual_ in their action
will force itself on our attention.
“What we have been long used to,” says Whytt, “we become scarcely
sensible of; while things which are new, though much more trifling,
and of weaker impression, affect us remarkably. Thus he who is wont to
spend his time in the country is surprisingly affected, upon first
coming into a populous city, with the noise and bustle which prevail
there: of this, however, he becomes daily less sensible, till at length
he regards it no more than they who have been used to it all their
lifetime. The same seems to be the case also with what passes within
our bodies. Few persons in health feel the beating of their heart,
though it strikes against their ribs with considerable force every
second; whereas the motion of a fly upon one’s face or hands occasions
a very sensible and uneasy titillation. The pulsation of the great
_aorta_ itself is wholly unobserved by us; yet the unusual beating of a
small artery in any of the fingers becomes very remarkable.”
7. A large amount of sensation is derived from the muscular sense, yet
we are not aware of the nice adjustments of the muscles, regulated by
this sensibility, when we sit or walk. No sooner are we placed in an
exceptional position, as in walking on a narrow ledge, than we become
distinctly aware of the effort required to preserve equilibrium. It is
not the novelty of the position which has increased our sensibility;
that has only caused us to attend to our sensations. In like manner,
the various streams of sensation which make up our general sense
of existence, separately escape notice until one of them becomes
obstructed, or increases in impetuosity. When we are seated at a
window, and look out at the trees and sky, we are so occupied with the
aspects and the voices of external Nature, that no attention whatever
is given to the fact of our own existence; yet all this while there
has been a massive and diffusive feeling arising from the organic
processes; and of this we become distinctly aware if we close our
eyes, shut off all sounds, and abstract the sensations of touch and
temperature--it is then perceived as a vast and powerful stream of
sensation, belonging to none of the special Senses, but to the System
as a whole. It is on this general stream that depend those well-known
but indescribable states named “feeling well” and “feeling ill”--the
_bien être_ and _malaise_ of every day. Of two men looking from the
same window, on the same landscape, one will be moved to unutterable
sadness, yearning for the peace of death; the other will feel his soul
suffused with serenity and content: the one has a gloomy background,
into which the sensations excited by the landscape are merged; the
other has a happy background, on which the sensations play like
ripples on a sunny lake. The tone of each man’s feeling is determined
by the state of his general consciousness. Except in matters of pure
demonstration, we are all determined towards certain conclusions as
much by this general consciousness as by logic. Our philosophy, when
not borrowed, is little more than the expression of our personality.
8. Having thus explained the relation of particular sensations to the
general state of Consciousness considered as the function of the whole
organism, we may henceforward speak of particular sentient states, as
we speak of particular organs and functions, all the while presupposing
that the organs and functions necessarily involve the organism, since
_apart_ from the organism they have no such significance. The reaction
of a sensory organ is therefore always a sentient phenomenon. Apart
from the living organism there can be no such vital reaction, but only
a physical reaction. It is commonly supposed that sensation is simply
the molecular excitation of the cerebrum; yet no one will maintain
that if the cerebrum of a corpse be excited, by a galvanic current
sent through the optic nerve, for instance, this excitation will be a
sensation. Whence we may conclude that it is not the physical reaction
or stimulus which constitutes sensation, but the physiological reaction
of the living organism.
9. Now this is the point which the advocates of the Reflex Theory,
implicitly or explicitly, always deny. Let us trace the origin of the
fallacy, if possible. When we remove the eye from a recently killed
animal, and let a beam of light fall on it, the pupil contracts. This
is a purely mechanical action; no one would suggest that a sensation
determined it. When we remove the leg, and irritate its nerve, the leg
is jerked out. This is also a purely mechanical action. When we remove
the brain from an animal, and pinch its toes, the leg is withdrawn
or the pincers are pushed aside. Is this equally a purely mechanical
action? And if not, why not?
The Reflex Theory would have us believe that all three cases were
mechanical, at least in so far as they were all destitute of sentient
co-operation, the ground for this conclusion being the hypothesis that
the brain is the exclusive seat of sensation. The Reflex Theory further
concludes that since these, and analogous actions, are performed when
the brain is removed, they, being thus independent of sentience, may
be performed when the brain is present without any co-operation of
sentience. The grounds for this conclusion being the facts that in
the normal state of the organism there are many actions of which we
are sometimes conscious, and at other times unconscious; and some
actions--such as the dilatation and contraction of the pupil--of which
we are never conscious. This observation of parts detached from the
organism seems confirmed by observation of actions passing in our
own organisms, both converging to the conclusion that the actions in
question are purely mechanical, involving no sentience whatever. We are
taught, therefore, that there is besides the sentient mechanism, to
which all conscious actions are referred, a reflex mechanism, to which
all unconscious actions are referred. The cerebro-spinal axis, acting
as a whole, constitutes the first; the spinal axis, acting without the
co-operation of the cerebrum, constitutes the second.
10. Before proceeding with our exposition of the theory it may be
well to state two considerations which must be constantly in view. If
it should appear that there is any reasonable evidence for refusing
to limit Sensibility to the cerebrum--and this evidence I shall
adduce--the Reflex Theory must obviously be remodelled. Nor is this
all. We might see overwhelming evidence in favor of the hypothesis that
the cerebrum is the exclusive seat of Sensibility, and still reject as
a fallacy the conclusion that because certain actions can be performed
in the absence of the cerebrum, therefore those actions in the normal
organism are likewise performed without cerebral co-operation. I
mean that it is a fallacy to conclude from the contractions of the
pupil, and the jerking of the leg, when eye and leg are detached
from the organism, that therefore when eye and leg form integral
parts of the organism, such contractions and jerkings are mechanical
reflexes without sentient conditions. And the fallacy is analogous
to that which would conclude from the observations of a mechanical
automaton, that similar appearances in a vital organism were equally
automatic and mechanical. So long as both sets of phenomena are
apprehended simply as they appear to the sense of sight, they may be
indistinguishable; but no sooner do we apprehend them through other
modes, and examine the _modes of production_ of the phenomena, than
we come upon cardinal differences. A limb detached from the organism
is like a phrase detached from a sentence: it has lost its vital
significance, its functional value, in losing its connection with the
other parts. The whole sentence is necessary for the slightest meaning
of its constituent words, and each word is a language-element only
when ideally or verbally connected with the other words required to
form a sentence; without subject, predicate, and copula, no sentence
can be formed. So the organic connexus of parts with a living whole is
necessary for the simplest function of each organ; and a limb, or any
other part, is a physiological element only when (ideally or really)
an integral of a vital whole. The organism may be truncated by the
removal of certain parts, as the sentence may be abbreviated by the
removal of certain phrases; but so long as subject, predicate, and
copula remain, there is a meaning in the sentence; and so long as the
organic connexus needful for vitality remains, there will be vital
function. The eye detached from the organism is no longer a part of
the living whole, it no longer lives, its phenomena cease to be vital,
its movements cease to have sentient conditions. The movements of the
pupil may seem to be the same as those of the living eye; but when we
come to examine their modes of production, we learn that they are not
the same. The stimulus of light falling on the eye in the two cases
necessarily has a different effect, because the effect is the result of
the co-operating causes, and the co-operation in the one case is that
of a lifeless organ, in the other that of a living organism. So long as
the eye forms an integral part of the organism, every stimulus acting
on the eye necessarily acts on the organism, and every reaction of the
organ is necessarily conditioned by the state of the organism. Further,
every stimulation of a sensory nerve necessarily affects the general
sensorium, since the whole nervous system is structurally continuous
and functionally co-operant. (See Prob. II. § 16.) Therefore, the
stimulation of the eye, although too faint to be discriminated as a
conscious sensation, must enter as a sentient tremor into the general
stream of Sentience; and although we have no test delicate enough to
reveal this operation, we know the _obverse_ operation of conscious
sensation on the movements of the pupil--in surprise, for example, the
pupil is dilated.
11. There are still stronger reasons for asserting that the spinal
reflexes are necessarily conditioned by the general state of the
sensorium, so that in the normal organism we cannot legitimately
exclude them from Sentience; and the Reflex Theory is therefore
unphysiological, even on the hypothesis that the cerebrum is the
exclusive seat of Sensibility. This hypothesis, however, seems to
me untenable; and all the observed facts which it is invented to
explain admit of a far more consistent explanation. It is irrational
to suppose that a limb, detached from the body, _felt_ the stimulus
which caused its muscles to contract. The limb is not a living
organism, having a sentient mechanism in its nervous mechanism. Not
less irrational is it to suppose that when the limb forms an integral
part of a living organism, with a sentient mechanism of nerves and
nerve-centres, this organism does not react on the stimulus which
excites the muscles of the limb to contract; nor, pursuing the same
train of reasoning, is it irrational to suppose that when this living
organism has been mutilated, and certain parts destroyed, which do
not in their destruction prevent the connexus of the rest, but leave
intact a sentient mechanism of nerves and nerve-centres, then also this
truncated organism still reacts as a whole, still feels the stimulus
which causes the muscles of the limb to contract. Hypothesis for
hypothesis, we may at least say that the one is as reasonable as the
other. And I shall be disappointed if, when the reader has gone through
all the evidence hereafter to be adduced, he does not conclude that
the hypothesis which assigns Sensibility to the nervous mechanism as a
whole is not the more acceptable of the two.
12. Let us now pursue our exposition of the Reflex Theory. All that
we have endeavoured to establish respecting the essential identity of
the processes in conscious and unconscious states, and voluntary and
involuntary actions,--an identity which does not exclude differences of
degree corresponding with these different terms,--is ignored or denied
in the Reflex Theory. Whereas I suppose all processes to be reflex
processes, some of them having the voluntary, others the involuntary
character, physiologists generally distinguish the involuntary as
reflex, and invent for this class a special mechanism. According to
Marshall Hall, who originated the modern form of this theory, actions
are divisible into four distinct classes: the _voluntary_, dependent
on the brain; the _involuntary_, dependent on the irritability of
the muscular fibre; the _respiratory_, wherein “the motive influence
passes in a _direct line_ from one point of the nervous system to
certain muscles”; and the _reflex_, dependent on the “true spinal
system” of _incident-excitor_ nerves, and of _reflex-motor_ nerves.
These last-named actions are produced when an _impression_ on the
sensitive surface is conveyed, by an excitor-nerve, to the spinal
cord, and is there _reflected_ back on the muscles by a corresponding
motor-nerve. In this process _no_ sensation whatever occurs. The action
is purely reflex, purely _excito-motor_--like the action of an ordinary
mechanism.[234]
Müller, who shares with Marshall Hall the glory of having established
this classification, thinks that although the absence of sensation is
a characteristic of the reflex actions, these actions may be, and are
at times, accompanied by sensation. “The view I take of the matter is
the following: Irritation of sensitive fibres of a spinal nerve excites
primarily a centripetal action of the nervous principle conveying the
impression to the spinal cord; if the centripetal action can then be
continued to the _sensorium commune_, a true sensation is the result;
if, on account of division of the cord, it cannot be communicated to
the sensorium, it still exerts its whole influence upon the cord; in
both cases a reflex motor action may be the result.”[235]
13. It is needless nowadays to point out that the existence of a
distinct system of excito-motor nerves belongs to Imaginary Anatomy;
but it is not needless to point out that the Imaginary Physiology
founded on it still survives. The hypothetical process seems to me not
less at variance with observation and induction, than the hypothetical
structure invented for its basis. We have already seen that what
Anatomy positively teaches is totally unlike the reflex mechanism
popularly imagined. The sensory nerve is not seen to enter the spinal
cord at one point, and pass over to a corresponding point of exit; it
is seen to enter the gray substance, which is continuous throughout the
spinal cord; it is there lost to view, its course being untraceable.
Nor does the physiological process present the aspect demanded by the
theory: it is not that of a direct and uniform reflexion, such as
would result from an impression on one spot transmitted across the
spinal cord to a corresponding motor-nerve. The impression is sometimes
followed by one movement, sometimes by another very different movement,
each determined by the state of neural tension in the whole central
system.
Even the facts on which the Reflex Theory is based are differently
interpreted by different physiologists. Van Deen, for instance,
considers that Reflexion takes place without Volition, but not
without Sensation; and Budge, that it takes place without perception
(_Vorstellung_). And when it is remembered that most of the reflex
actions will be accompanied by distinct consciousness whenever
attention is directed to them, or the vividness of the stimulation
is slightly increased, it becomes evident that the absence of
Consciousness (discrimination) is not the differentia of Reflex action.
14. Nor can the absence of spontaneity be accepted as a differentia.
_All_ actions are excited by stimulation, internal or external. What
are called the spontaneous actions are simply those which are prompted
by internal, or by not recognizable stimuli; and could we see the
process, we should see a neural change initiated by some stimulation,
whether the change was conscious and volitional, or unconscious and
automatic. The dog rising from sleep and restlessly moving about,
is acting spontaneously, whether the stimulation which awakens him
be a sensation of hunger, a sensation of sound, the sharp pain of a
prick, or a dash of cold water. If he wags his tail at the sight of
his master, or wags it when dreaming, the stimulation is said to be
spontaneous; but if after his spinal cord has been divided the tail
wags when his abdomen is tickled, the action is called reflex. In all
three cases there has been a process of excitation and reflexion.
15. The advocates of the Reflex Theory insist that spontaneity is
always absent in brainless animals; whence the conclusion that the
brain is the exclusive organ of sensation. But the fact asserted is
contradicted by the evidence. No experimenter can have failed to
observe numberless examples of spontaneity in brainless animals. Many
examples have already been incidentally noticed in previous pages. Let
me add one more from my notes: I decapitated a toad and a triton, and
divided the spinal cord of another triton and a frog. At first the
movements of the decapitated animals were insignificant; but on the
second day the headless toad was quite as lively as the frog; and the
headless triton little less so than his companion with cord divided
but brain intact. I have, at the time of writing this, a frog whose
cord was divided some weeks ago. He remains almost motionless unless
when touched; he is generally found in the same spot, and in the same
attitude to-day as yesterday, unless touched, or unless the table be
shaken. He occasionally moves one of the forelegs; occasionally one of
the hind-legs; but without changing his position. If he were brainless,
this quiescence would be cited in proof of the absence of spontaneity
in the absence of the brain; but this conclusion would be fallacious,
and is seen to be so in the spontaneous movements of his companion who
has _no_ brain.
16. With spontaneity is associated the idea of volition, and with
volition _choice_. Now I admit that it is complicating the question to
ask any one to conceive a headless animal choosing one action rather
than another; but it is equally difficult to reconcile ourselves to
the idea of “choice” in contemplating the actions of a mollusc. In
what sense we can speak of the volition of a mollusc or an insect has
already been considered (p. 408). When a man in a fit of coughing
seizes a glass of water to allay the tickling in his throat, we have
no hesitation in declaring this to be volitional--and the remedy to
be _chosen_. But when a brainless animal adopts some _unusual_ means,
after the failure of the usual means, to allay an irritation, we still
hesitate to call the action volitional. I see, however, no objection to
calling it the adaptation of a sensitive mechanism which is markedly
unlike any inorganic mechanism.
Place a child of two or three years old upon his back, and tickle
his right cheek with a feather. He will probably move his head away.
Continue tickling, and he will rub the spot with his right hand,
_never_ using the left hand for the right cheek, so long as the right
hand is free; but if you hold his right hand, he will use the left.
Does any one dispute the voluntary character of these actions?
Now compare the actions of the sleeping child under similar
circumstances, and their sequence will be precisely similar. This
contrast is the more illustrative, because physiologists generally
assume that in sleep consciousness and volition are _suspended_.
They say: “The brain sleeps, the spinal cord never; volition and
sensation may be suspended, but not reflex action.” This proposition is
extremely questionable; yet it is indispensable to the reflex theory;
because unless sensation and volition _are_ suspended during sleep, we
must admit that they can act, without at the same time calling into
activity that degree of sensibility which is supposed to constitute
consciousness. The child moves in his sleep, defends himself in his
sleep; but he is not “aware” of it.
“Children,” says Pflüger, “sleep more soundly than adults, and seem
to be more sensitive in sleep. I tickled the right nostril of a
three-year-old boy. He at once raised his right hand to push me away,
and then rubbed the place. When I tickled the left nostril he raised
the left hand. I then softly drew both arms down, and laid them close
to the body, embedding the left arm in the clothes, and placing on it a
pillow, by gentle pressure on which I could keep the arm down without
awakening him. Having done this I tickled his left nostril. He at once
began to move the imprisoned arm, but could not reach his face with
it, because I held it firmly though gently down. He now drew his head
aside, and I continued tickling, whereupon he raised the _right_ hand,
and with it rubbed the _left_ nostril--an action he never performed
when the left hand was free.”
17. This simple but ingenious experiment establishes one important
point, namely, that the so-called reflex actions observed in sleep
are determined by sensation and volition. The sleeping child behaves
exactly as the waking child behaved; the only difference being in
the energy and rapidity of the actions. If the waking child felt and
willed, surely the sleeping child, when it performed precisely similar
actions, cannot be said to have felt nothing, willed nothing? It is
not at one moment a sentient organism, and at the next an insentient
mechanism.
It is possible to meet this case by assuming that the child was nearly
awake, and that a dim consciousness was aroused by the tickling, so
that the cerebral activity was in fact awakened. But, plausible as
this explanation may be (and I am the more ready to admit it because I
believe the brain always co-operates when it is present), it altogether
fails when we come to experiments on decapitated animals. If any one
will institute a series of such experiments, taking care to compare the
actions of the animal before and after decapitation, he will perceive
that there is no more difference between them than between those of the
sleeping and the waking child.
18. Even more striking is the following experiment, devised by Pflüger,
which I have verified, and varied, many times: A frog is decapitated,
or its brain is removed.[236] When it has recovered from the effect of
the ether, and manifests lively sensibility, we place it on its back,
and touch, with acetic acid, the skin of its thigh just above the
_condylus internus femoris_. (Let the reader imagine his own shoulder
burnt at the point where it can be reached with the thumb of the same
arm, and he will realize the operation.) No sooner does the acid begin
to burn than the frog stretches out the _other_ leg, so that its body
is somewhat drawn towards it. The leg that has been burnt is now bent,
and the back of the foot is applied to the spot, rubbing the acid
away--just as your thumb might rub your shoulder. This is very like
the action of the tickled child, who always uses the right hand to rub
the right cheek, unless it be held; but when the child’s right hand is
prevented from rubbing, the left will be employed; and precisely this
do we observe with the brainless frog: prevent it from using its right
leg, and it will use its left!
This has been proved by decapitating another frog, and cutting off
the foot of the leg which is to be irritated. No sooner is the acid
applied, than the leg is bent as before, and the stump is moved to and
fro, as if to rub away the acid. But the acid is not rubbed away, and
the animal becomes restless, as if trying to hit upon some other plan
for freeing himself of the irritation. And it is worthy of remark that
he often hits upon plans very similar to those which an intelligent
human being adopts under similar circumstances. Thus, the irritation
continuing, he will sometimes cease the vain efforts with his stump,
and stretching that leg straight out, bends the _other_ leg over
towards the irritated spot, and rubs the acid away. But, to show how
far this action is from one of “mere mechanism,” how far it is from
being a direct reflex of an impression on a group of muscles, the
frog does not _always_ hit even on this plan. Sometimes it bends its
irritated leg more energetically, and likewise bends the body towards
it, so as to permit the spot to be rubbed against the flank--just as
the child, when both his hands are held, will bend his cheek towards
his shoulder and rub it there.
19. It is difficult to resist such evidence as is here manifested. The
brainless frog “chooses” a new plan when the old one fails, just as
the waking child chooses. And an illustration of how sensations guide
and determine movements, may be seen in another observation of the
brainless frog, when, as often happens, it does not hit upon either of
the plans just mentioned, but remains apparently restless and helpless;
if under these circumstances we perform a part of the action for it,
_it will complete what we have begun_: if we rub the irritated leg, at
some distance from the spot where the acid is, with the foot of the
other, the frog suddenly avails itself of this _guiding sensation_, and
at once directs its foot to the irritated spot.
In these experiments on the triton and the frog, the evidence of
sensation and volition is all the stronger, because the reactions
produced by irritations are not uniform. If when a decapitated animal
were stimulated it always reacted in _precisely the same way_, and
never chose _new means_ on the failure of the old, it would be
conceivable to attribute the results to simple reflex action--i. e. the
mechanical transference of an impulse along a prescribed path. It is
possible so to conceive the breathing, or the swallowing mechanism: the
impression may be directly reflected on certain groups of muscles. But
I cannot conceive a machine suddenly striking out new methods, when the
old methods fail. I cannot conceive a machine thrown into disorder when
its accustomed actions fail, and in this disorder suddenly lighting
upon an action likely to succeed, and continuing _that_; but I can
conceive this to be done by an organism, for my own experience and
observation of animals assures me that this is always the way new lines
of action are adopted. And this which is observed of the unmutilated
animal, I have just shown to be observed of the brainless animal;
wherefore the conclusion is, that if ever the frog is sentient, if
ever its actions are guided by sensation, they are so when its brain is
removed.
20. Schröder van der Kolk thinks that Pflüger was deceived in
attributing sensation and volition to the frog, because the reflex
actions are, he says, so nicely adapted to their ends, that they are
undistinguishable from voluntary actions. The mechanism is such that,
by means of the communications established between various groups of
cells, all these actions adapted to an end may be excited by every
stimulus. But I deny the fact. I deny that all the actions are awakened
by every stimulus. Only some few are awakened, and those are not
always the same, nor do they follow the same order of succession. One
decapitated frog does not behave exactly like another under similar
circumstances; does not behave exactly like himself at different
seasons; unlike a machine, he manifests spontaneity in his actions, and
volition in the direction of his actions.
21. The reader will notice that my illustrations show these actions of
the brainless animal to have the same external characters as those of
the unmutilated animals. I am therefore not here concerned to prove
the psychical nature of these actions, unless it be granted that the
unmutilated animal has sensation and volition. This of course can
only be inferred, not proved. But the inference must not be allowed
in the one case and refused in the other. Young rabbits and puppies
when taken from their mothers manifest discomfort by restless movement
and whining. Do they feel the discomfort they thus express? If ever
rabbits and puppies may be said to feel, we must answer, Yes. Well,
if the brain be removed from rabbits and puppies, precisely similar
phenomena are observed when these young animals are taken from
their mothers. “I observed the motions, which seemed the result of
discomfort, quickly cease when I warmed the young rabbit by breathing
on it. After a while it was completely at rest, and seemed sunk in
deep sleep; occasionally, however, it moved one of its legs without
any external stimulus having been applied, and this not spasmodically,
but in the manner of a sleeping animal.”[237] Is this cessation of
the restlessness, when warmth is restored, not evidence of sensation?
We see an infant restless, struggling, and squalling; and we believe
that it is hungry, or that some other sensations agitate it; it is
put to the breast, and its squalls subside; or a finger is placed in
its mouth, and it sucks that, in a peaceful lull, for a few moments,
to recommence squalling when the finger yields no satisfaction. If we
accept these as signs of sensation, I do not see how we can deny such
sensation to the brainless animal which will also cease to cry, and
will suck the delusive finger.
22. One of the earliest advocates of the Reflex Theory sums up
his observations in these words: “It is clear that brainless
animals, although without sensation, because not endowed with
mind, nevertheless, by means of external impressions which operate
incessantly on them, perform all the acts and manifest all the activity
of the sentient animal; everything that is effected sensationally
and volitionally, they effect by means of the organic forces of the
impressions.”[238] Call Sensibility one of the organic forces, if you
please, but so long as the acts performed are not only the same as
those of a sentient animal, but are performed by the same mechanism,
they have every claim to the character of sensational acts which can be
urged in the case of these animals when the brain is present. And the
only reason on which this claim is disputed is the assumed loss of all
sensation with the loss of the brain. Here, therefore, lies the central
point to be determined.
CHAPTER II.
DEDUCTIONS FROM GENERAL LAWS.
23. The evidence is of two kinds: deductions from the general laws of
nervous action, and inductions from particular manifestations. The
former furnish a presumption, the latter a proof.
The central process which initiates a reflex action may be excited
by the external stimulation of a peripheral nerve, by the internal
stimulation of a peripheral nerve, or by the irradiation from some
other part of the central tissue. The last-named stimulations are
the least intelligible, because they are so varied and complex,
and so remote from observation; among them may be placed, 1°, the
organized impulses of Instinct and Habit, with their fixed modes of
manifestation; 2°, the organized impulses of Emotion, which are more
variable in their manifestations, because more fluctuating in their
conditions; 3°, the organized impulses of Intellect, the most variable
of all. Whether we shrink on the contact of a cold substance or on
hearing a sudden sound,--at the sight of a terrible object,--at the
imaginary vision of the object,--or because we feign the terror which
is thus expressed,--the reflex mechanism of shrinking is in each case
the same, and the neural process discharged on the muscles is the same;
but the state of Feeling which originated the change--or, in strictly
physiological terms, the inciting neural process which preceded this
reflex neural process--was in each case somewhat different, yet in each
case was a mode of Sensibility.
24. The property of Sensibility belongs to the whole central tissue;
and we have every reason to believe that unless it is excited no reflex
takes place, whereas when it is exaggerated--as in epilepsy, or under
strychnine--the reflex discharges are convulsive. When anæsthetics are
given, consciousness first disappears, and then reflexion. When the
sensorium is powerfully excited by _other_ stimuli, the normal stimulus
fails to excite either consciousness or reflexion. Hence our conclusion
is that for consciousness, on the one hand, and _normal_ reflexion, on
the other, the proximate condition is a change in the sensorium; or--to
phrase it more familiarly--Feeling is necessary for reflex action.
The difficulty in apprehending this lies in the ambiguity of the
term Feeling. Many readers who would find no difficulty in admitting
Sensibility as a necessary element in reflex action, will resist the
idea of identifying Sensibility with Feeling. But this repugnance must
be overcome if we are to understand the various modes of Sensibility
which represent Feeling in animals, and its varieties in ourselves. We
understand how the general Sensibility manifests itself in markedly
different sensations--how that of the optic centre differs from that
of the auditory centre, and both from a spinal centre. The tones of a
violin are not the same as the tones of a violoncello, both differ from
the tones of a key-bugle: yet they all come under the same general laws
of tonality. So, as I often insist, the tissues in brain and cord being
the same, their properties must be the same, their laws of excitation,
irradiation, and combination the same, through all the varieties in
their manifestations due to varieties of innervation. Hence it is
that there are reflex cerebral processes no less than reflex spinal
processes: the motor impulse from, the hemispheres on the _corpora
striata_, or from posterior gray substance on anterior gray substance,
is similar to that from the anterior gray substance on the motor
nerves. The difference in reflexes arises from the terminal organs; as
the difference in sensations arises from the surfaces stimulated. But
not only are there reflex processes in the brain, of the same _order_
as those in the cord, there are volitional processes in the cord of
the same order as those in the brain. And in both the processes are
sometimes conscious, sometimes unconscious. No evidence suggests that
in the conscious action there is a sensorial process, and a purely
physical process in the unconscious action--only a different _relation_
of one sensorial process to others.
25. Let us contrast a cerebral and a spinal process, in respect to the
three stages of stimulation, irradiation, and discharge. A luminous
impression stimulates my retina, this excites my sensorium, in which
second stage I am conscious of the luminous sensation; the final
discharge is a perception, or a mental articulation of the _name_ of
the luminous object. But the irradiation may perhaps not have been
such as to cause a _conscious_ sensation, because the requisite neural
elements were already grouped in some other way; in this case there is
an unconscious discharge on some motor group, and instead of perceiving
and naming the luminous object, I move my head, or my band, or my
whole body, avoiding the object, or grasping at it. A third issue is
possible: the irradiation, instead of exciting a definite perception,
or a definite movement, may be merged in the stream of simultaneous
excitations, and thus form the component of a group, and the discharge
of this group will be a perception or a movement.
It is the same with a spinal process. An impression on the skin is
irradiated in the cord, and the response is a movement, of which we
are conscious, or unconscious. Here also a third issue is possible:
the irradiation may be merged in a stream of simultaneous excitations,
modifying them and modified by them, thus forming a component in some
ulterior discharge.
26. The obstacle in the way of recognizing that cerebral processes and
spinal processes are of the same order of sensorial phenomena, and have
the same physiological significance when considered irrespective of the
group of organs they call into activity, is similar to the obstacle
which has prevented psychologists from recognizing the identity of the
logical process in the combinations of Feeling and the combinations
of Thought, i. e. the Logic of Feeling and the Logic of Signs. This
obstacle is the fixing attention on the diversity of the effects when
the same process operates with different elements. Because the spinal
cord manifests the phenomena of sensation and volition, we are not to
conclude that it also manifests ideation and imagination; any more
than we are to conclude that a mollusc is capable of musical feelings
because it is affected by sounds.
27. The careless confusion of general properties with special
applications of those properties, and of functions with properties, has
been a serious hindrance to the right understanding of Sensibility and
its operations. Instead of recognizing that the nervous system has one
general mode of reaction, which remains the same under every variety
of combination with other systems, physiologists commonly lose sight
of this general property, and fix on one mode of its manifestation as
the sole characteristic of Sensibility. Sometimes the mode fixed on
is Pain, at other times Attention. Thus, when an animal manifests no
evidence of pain under stimulations which ordinarily excite severe
pain, this is often interpreted as a proof that _all_ sensation is
absent; and if with this absence of pain there is--as there often
is--clear evidence of the presence of some other mode of sensibility,
the contradiction is evaded by the assumption that what here looks like
evidence of sensation is merely mechanical reflexion. One would think
that Physiology and Pathology had been silent on the facts of analgesia
without anæsthesia, and of so much conscious sensation which is
unaccompanied by pain.[239] Who does not know that a patient will lose
one kind of sensibility while retaining others--cease to feel pain,
yet feel temperature, or be insensible to touch, yet exquisitely alive
to pain?[240] Inasmuch as Sensibility depends on the condition of the
centres, an abnormal condition will obviously transform the reaction
of the centres into one very unlike the normal reaction. For example,
Antoine Cros had a patient who was quite unable to feel the sensation
of cold on her left side--every cold object touching her skin on that
side was felt as a very hot one; whereas a hot object produced “the
sort of sensation which followed the application of an intermittent
voltaic current.”[241] Thus also the experiments of Rose[242] and
others have exhibited the effects of a dose of Santonine in causing all
objects to be seen as yellow in one stage, and violet in another.
28. If, then, certain alterations in the organic conditions are
accompanied by a suppression or perversion of some modes of
Sensibility, without suppressing the rest, it is but rational to
suppose that profound disturbances of the organic mechanism, such
as must result from the removal of the brain, will also suppress or
pervert several modes of Sensibility, and yet leave intact those
modes which belong to the intact parts of the mechanism. Assuming
that the spinal centres with the organs they innervate are capable of
reacting under certain modes of sensation, these will not necessarily
be suppressed by removal of the brain--all that will thereby be
suppressed is their co-operation with the brain. I know it will be
said that precisely this co-operation is necessary for sensation; and
that the spinal reactions are simple reflexions in which sensation has
no part. This, however, is the position I hope to turn. Meanwhile my
assumption is that sensation necessarily plays a part in the reflex
actions _of the organism_, and when that organism is truncated, its
actions are proportionately limited, its sensations less complex. The
spinal cord, separated from encephalic connections, cannot react in the
special forms of Sensation known as color, scent, taste, sound, etc.,
because it does not innervate the organs of these special senses, nor
co-operate with their centres. But it can, and does, react in other
modes: it innervates skin and muscles; and the sensibilities, thus
excited, it can also _combine_ and _co-ordinate_. It has its Memory,
and its Logic, just as the brain has: both no longer than they are
integral parts of an active living organism: neither when the organism
is inactive or dead. We do not expect the retina to respond in sounds,
nor the ear to respond in colors: we expect each organ to have its
special mode of reaction. What is common to both is Sensibility.
What is common to brain and cord is Sensibility--and the laws of
Grouping. Instead of marvelling at the disappearance of so many modes
of Sensibility when the brain is removed, our surprise should be to
find so many evidences of Sensibility remaining after so profound a
mutilation of the mechanism.
29. The current hypothesis, which assumes that the brain is the sole
organ of the mind, the sole seat of sensation, is a remnant of the
ancient hypothesis respecting the Soul and its seat; and on the whole
I think the ancient hypothesis is the more rational of the two. If the
Soul inhabits the organism, using it as an instrument, playing on its
organs as a musician plays on his instrument, we are not called upon
to explain the mode of operation of this mysterious agent; but if the
Soul be the subjective side of the Life, the spiritual aspect of the
material organism, then since it is a synthesis of all the organic
forces, the consensus of all the sentient phenomena, no one part can
usurp the prerogatives of all, but all are requisite for each. And
this indeed is what few physiologists would nowadays dispute. In spite
of their localizing sensation in the cerebral cells, they would not
maintain that the cerebral cells, nor even the whole brain, could
produce sensation--if _detached_ from the organism; the cheek of the
guillotined victim may have blushed when struck, but who believes that
the brain felt the insult, or the blow? Obviously, therefore, when we
read that thought is “a property of the gray substance of the brain, as
gravitation is of matter,” or that the brain is the exclusive organ of
Sensation, the writers cannot consistently carry out their hypothesis
unless they silently reintroduce other organs as co-operating agents;
for a neural process in the cerebrum is _in itself_ no more a
sensation than it is a muscular contraction, or a glandular secretion:
the muscles must co-operate for the contraction, the gland for the
secretion, the neural process being simply the exciting cause. In
like manner the Sensorium is necessary for the sensation, the neural
process--in cerebrum, or elsewhere--being simply the exciting cause.
30. And what is the Sensorium? A long chapter would be required
to state the various opinions which have been held respecting its
_seat_, although amid all the disputes as to the organ, there has been
unanimity as to the function, which is that of converting stimulations
into sensations. I cannot pause here to examine the contending
arguments, but must content myself with expounding the opinion I hold,
namely, that the Sensorium is the _whole_ of the sensitive organism,
and not any one isolated portion of it. When light falls on the optic
organ, or air pulses on the auditory organ, the reaction of each organ
determines the _specific_ character of the sensation, _but no such
sensation is possible unless there be a reaction of the organism_;
and the nature of the product will of course vary with the varying
factors which co-operate--a simple organism, a truncated organism, an
exhausted or otherwise occupied organism, will react differently from
a complex, a normal, or an unoccupied organism. Detach the optic organ
with its centre from the rest of the organism, and no normal sensation
of Sight will result from its stimulation; and in a lesser degree this
is equally true of a stimulation of the optic organ when the sensorium
is exhausted, or powerfully affected by other stimuli. Because of the
great importance of the cerebrum, and its predominance in the nervous
system, it has been supposed to constitute the whole of the sensorium,
in spite of the evidence of varied Sensibility after the cerebrum has
been removed. I do not wish to understate the cerebral importance (see
p. 166), yet I must say that the modern phrase _cerebration_, when
employed as more than a shorthand expression of the complex processes
which a cerebral process initiates, and when taken as the objective
equivalent of Consciousness or of Thought, seems to me not more
justifiable than to speak of Combustion as the equivalent of Railway
Transport. The railway wagons will not move unless the fuel which
supplies the boiler be ignited; the organism will not think unless the
cerebrum excites this peculiar mode of Sensibility by its action on
the organs. _It is the man, and not the brain, that thinks_: it is the
organism as a whole, and not one organ, that feels and acts.
31. Consciousness, or Sensation, is a complex product not to be
recognized in any _one_ of its factors. Cerebral processes and spinal
processes are the elements we analytically separate, as muscular
contractions are the elements of limb-movements. The synthetic unity
of these elements is a reflex; this we analytically decompose into
a sensation and a movement; and then we speak of sensation as the
reaction of the sensory organ, the movement as the reaction of the
muscular organ. By a similar procedure we separate the stimulation of
a sensory nerve from the reaction of the sensory organ, and that from
the reaction of the sensorium; and in this way we may come to regard
Cerebration as Thought. But those who employ this artifice should
remember that the organism is not an assemblage of organs, made up of
parts put together like a machine. The organs are differentiations of
the organism, each evolved from those which preceded it, all sharing in
a common activity, all _inter_-dependent.
32. That co-operation of the Personality which is conspicuous in
conscious actions is also inductively to be inferred in sub-conscious
and unconscious actions. We know that a man reacts on an impression
according to his physical and mental state at the moment--that through
his individuality he feels differently, and thinks differently from
other men, and from himself at other epochs, and in other states.
Because he resembles other men in many and essential points we
conclude that he will resemble them in all; but observation proves
this conclusion to be precipitate. Other men see a blue color in the
sky, or feel awe at sight of the setting sun; but he has perhaps
not learned to discriminate this sensation, is not conscious of the
blue; nor has he learned to feel awe at the setting sun. Why--having
normally constructed eyes--does he not see the blue of the sky? For the
same reason that a dog, or an infant, fails to see it. The color has
no _interest_ for him (and all cognition is primarily emotion), nor
has this want of personal interest been rectified from an impersonal
source: he has never been taught to distinguish the color of the sky;
and his eye wanders over it with the indifferent gaze with which a
savage would regard a Greek codex.
33. The point here insisted on, namely, that every reaction on an
impression is indirectly the reaction of the whole organism, and that
no organ detached from the organism has more significance than a word
detached from a sentence, is of far-reaching importance, and peculiarly
worthy of attention in considering the Reflex Theory, because almost
all the evidence urged in support of that theory presupposes the
legitimacy of concluding what takes place in the organism from what
is observed in an organ detached from its normal connections. No
experimental proof is necessary to show that many actions take place
unconsciously; the fact is undisputed. But does unconsciously mean
insentiently? It is certain that the unconscious actions take place in
a sentient organism, and involve organic processes of the same _order_
as the actions which are conscious. It is also certain that many
sentient processes take place unconsciously. For thousands of years men
used their eyes, and saw as their descendants see, yet were unconscious
of the blue sky and green of the grass. Were their visual reactions
not of the same _order_ as our own? So far as the optic apparatus
is concerned, there cannot be a doubt on the point; yet in them the
sensorium having a somewhat different disposition--the neural elements
being differently combined--their reactions correspondingly differed.
They too had optical Sensibility, and visual sensations; but they did
not feel precisely what we feel.
34. I have chosen these somewhat remote illustrations for the sake of
their psychological interest; but I might have confined myself to more
familiar examples. Thus the contents of the consciousness of a man born
blind cannot be _the same_ as the contents of one who has had visual
experiences, which will enter into the complex of every conscious
state, because the visual organs will have affected his sensorium;
nevertheless in the organism of the blind man there are conditions
so similar to those of other men, and his experiences will have been
so similar, that in spite of the modifications due to the absence of
visual experiences, his consciousness will in the main resemble theirs.
But now let us in imagination pursue this kind of modification, let us
take away hearing, taste, and smell, and we shall have proportionately
simplified the contents of consciousness--the reactions of the
sensorium--in thus simplifying the organism. There still will remain
Touch, Temperature, Pain, and the Systemic Sensations. There will still
remain an organism to react on impressions. So long as there is a
living organism, however truncated, there is a sentient mechanism. When
the brain has been removed, the removal causes both a _disturbance_ of
function and a _loss_ of function; the mechanism has been seriously
interfered with; yet all those parts of the mechanism which still
co-operate manifest their physiological aptitudes. The animal can live
without its brain, _ergo_ it can feel without its brain. Observation
proves this, for it discovers the brainless animal manifesting various
sensibilities, and combining various movements. The vision of the
brainless animal is greatly impaired, but it nevertheless persists.
The intelligence is greatly impaired, the spontaneity is reduced to a
minimum; but still both intelligence and spontaneity are manifested.
35. The physiologist has only two conclusions open to him. Either
he holds Sensation to be a _property_ of nerve-tissue--and in that
case he must assign it to the spinal cord as to the brain; or else
he holds Sensation to be a _function_ of an organ--and in that case,
although analytically he may decompose the organism into separate
organs, assigning special sensations to the reactions of each, he must
still admit that in reality these organs only yield sensations as
component parts of the organism. The notion of a separate organ, such
as the brain, being the exclusive seat of sensation is thus seen to be
untenable.
In popular phrase, “it is not the eye which sees, but the mind behind
the eye.” It is not the stimulus which is the _object_ felt--it is the
change in consciousness--the reaction of the sensorium. No one would
propound the absurdity that the retinal cells _see_, or the auditory
cells _hear_ (although by a conventional ellipsis these cells are said
to be “percipient” of colors and sounds), yet many writers have no
hesitation in asserting that the cerebral cells are the seats of these
and all other sensations. In a hundred treatises may be read the most
precise description of the transformation of molecular changes in the
retinal cells into molecular changes in the cerebral cells, where, it
is said, “we know that the stimulations become sensations.” Now who
knows this? How can it be known? Nay, who, on reflection, fails to see
that this cannot be so? If a sensation of sight were not much _more_
than a molecular change in the cerebrum stimulated by a molecular
change in the optic tract, three conclusions would follow, each of
which is demonstrably erroneous:--
I. The cerebrum in a decapitated animal would respond by a sensation of
sight to a retinal stimulation.
II. The animal deprived of its cerebrum could not respond by a
sensation of sight to a retinal stimulation.
III. The same retinal stimulation would always produce the same
cerebral process and the same sensation; whereas the sensation depends
on the condition of the sensorium at the time.
36. The difference between the Reflex Theory and that here upheld is
important in its general relations, and yet turns on a point which may
easily appear insignificant. The Reflex Theory asserts that when a
sensory nerve is stimulated, the excitation of the centre may either
subdivide into two waves, one of which passes directly to the brain
and there awakens sensation, the other passes over to the motor-roots
and causes muscular contractions; or, instead of thus subdividing, the
wave may pass at once to the motor-nerves, and then there is movement
without sensation. This is obviously a restatement in anatomical terms
of the observed fact that some reflexes take place consciously and
some unconsciously. But what evidence is there for this anatomical
statement? We have seen that there is none. According to all we
actually know, and reasonably infer, the continuity of tissue and the
irradiation of excitation are such that the stimulus wave must always
affect the whole system, so that brain and cord being structurally
united, their reactions must co-operate with varying energy dependent
on their statical conditions at the time.[243]
37. The physiological fact that the irradiation is _restricted_ to
certain paths, and therefore only certain portions of the whole system
are excited to discharge--the fact that stimulation takes effect along
the lines of least resistance--is that which gives the Reflex Theory
its plausible aspect. But this fact of restriction is not dependent on
an _anatomical_ disposition of structure, it is, as we have already
seen (PROBLEM II. § 166), dependent on a fluctuating physiological
disposition--a temporary statical condition of the centres. And it
enables us to understand why the reflex action which is at one moment
a distinctly conscious or even a volitional action, is at another
sub-conscious or unconscious. When an object is placed in the hand of
an infant the fingers close over it by a simple reflex. This having
also been observed in the case of an infant born without a brain,[244]
one might interpret it as normally taking place without brain
co-operation, were there not good grounds for concluding that normally
the brain must co-operate. Thus if the object be placed in the hand of
a boy, or a man, the fingers will close, or not close--not according to
an anatomical mechanism, but according to a physiological condition:
if the attention preoccupy his sensorium elsewhere, his fingers will
probably close, probably not; if his sensorium be directed towards the
object, either by the urgency of the sensitive impression, or by some
one’s pointing to the object, the fingers will close or not close,
just as he chooses--perhaps the hand will be suddenly drawn away. The
centre of innervation for the fingers is in the cord, and from this
comes the final discharge of the sensitive stimulation; but the neural
processes which preceded this discharge, and were consequent on the
stimulation, were in each case somewhat different. In each case the
impression on the skin was carried to the cord, and thence irradiated
throughout the continuous neural axis, restricted to certain paths by
the resistance it met with, but blending with waves of simultaneous
excitations from other sources, the final discharge being the resultant
of these component forces. We may suppose the brain to be the seat
of consciousness, and yet not conclude that the brain was unaffected
because the fingers closed unconsciously; any more than we conclude
that the retina of the unoccupied eye is unaffected by light when with
the other we are looking through a microscope, and only _see_ objects
with this eye--though directly we attend to the impressions on the
other eye we see the objects which before were unseen. We know that the
muscles of the back are all involved in walking, standing, etc., but we
are seldom conscious of their co-operation till rheumatism or lumbago
makes us painfully alive to it.
38. The two main positions of the Reflex Theory are, 1°, that
reflex actions take place without brain co-operation,--as proved by
observation of decapitated animals; 2°, that they take place without
brain co-operation,--as proved by our being unconscious of them.
To these the answers are: 1°. The proof drawn from observation of
decapitated animals is defective, because the conditions of the
organism are then abnormal--there is a disturbance of the mechanism,
and a loss of some of its components. The fact that a reflex occurs
in the absence of the brain is no proof that reflexes when the brain
is present occur without its participation. 2°. The absence of
consciousness cannot be accepted as proof of the brain not being in
action, because much brain-work is known to pass unconsciously, and
there are cerebral reflexes which have the same characters as spinal
reflexes.
39. A prick on the great toe traverses the whole length of the spinal
axis with effects manifested in various organs--the muscles of the
limb, the heart, the chest, the eyes, etc. The leg is withdrawn,
the heart momently arrested, the eyes turned towards the source of
irritation, the thoughts directed towards relief. These effects can
be observed--there are others which lie beyond our observation, and
can only be revealed by delicate experimental tests. But even the
observable effects are very fluctuating, because they depend on
fluctuating conditions. All we can say is, that so long as there is
continuity of structure, there must be continuity of excitation;
and the brain structurally connected with the centre of a sensory
impression, must necessarily co-operate more or less in the reactions
of that centre. In other words, the brain, although not the exclusive
seat of sensation, plays a part in every particular sensation, so long
as it forms a part of the stimulated organism.
40. This view being so widely opposed to the views current in
physiological schools, I was gratified to find Dr. Crichton Browne led
by his researches to a conclusion not unlike it in essential features.
In his essay on the Functions of the Optic Thalami[245] (well worthy
of attention on other grounds) he says: “Allowing the spinal cord a
power of independent action, it may still be that it generally acts
reflexly through, or in association with, a superior centre. The
sensorial ganglia can undoubtedly act alone in a reflex manner, but
they almost invariably consult the cerebrum before dealing with the
impressions which they receive; so it may be that the spinal cord,
though capable of spontaneous reaction, may yet commonly refer to some
higher seat of compound co-ordination before sending forth an answer
to any message brought to it.” What is here stated as a possible and
occasional process, I consider to be a necessary and universal process.
Dr. Browne acutely remarks that if “what may be termed the encephalic
loop were an integral part of every reflex act, then the influence of
an intracranial lesion in checking reflex action would not be difficult
to understand”--and we may add the notorious influence of the brain in
arresting reflex actions, and modifying them by the will, which is only
explicable on the supposition that the cerebral and spinal centres are
functionally associated. Dr. Browne further remarks: “In experimenting
upon myself I have sometimes thought that when the toe is pricked the
sensation of pain actually precedes the movement of withdrawal; and
in experimenting upon patients with sluggish nervous systems I have
certainly noticed that after the pricking of the toe the little cry of
pain has anticipated the muscular contractions of the leg. Now this cry
of pain is a secondary reflex act through the sensorial centre; it is
the result of a discharge from efferent nerves from the summit of what
we have spoken of as the encephalic loop line; and we should certainly
not expect that it would be developed earlier than the primary
reflexion upon the motor apparatus, unless indeed what we have regarded
as the primary reflexion really itself took place by way of the loop
line.”
41. The difference between a voluntary and involuntary act is not, I
conceive, that in the one case the brain co-operates and in the other
is inactive, but that while in both the brain co-operates, the state
of the sensorium known as mental prevision or ideal stimulation, is
present in the one, and absent or less conspicuous in the other. So
likewise the difference between a normal reflex action accompanied, and
the same action unaccompanied by consciousness, is not that the brain
co-operates in the one and is inactive in the other, but that the state
of the sensorium is somewhat different in the two cases. Movements
which originally were voluntary and difficult of execution--accompanied
therefore by brain co-operation--become by frequent repetition
automatic, easy of execution, and unconscious--they are then said to
depend on the direct action of the established mechanism. Granted. But
what are the components of this mechanism? Are they not just those
centres and organs which at first effected the movements? In becoming
easy and automatic, the movements do not _change their mechanism_--the
moving organs and the motor conditions remain what they were; all that
is changed is the degree of consciousness, i. e. the _state_ of the
sensorium which precedes and succeeds the movement. It is this which
constitutes the difficulty of the question. Some readers may consider
that all is conceded when unconsciousness is admitted. But this is
not so. My present argument is the physiological one that the brain
co-operates in reflex actions whenever the brain is structurally united
with the reflex centres; the psychological question as to whether
consciousness is also involved in this brain co-operation must be
debated on other grounds; and we have already seen that consciousness
operates in gradations of infinite delicacy.
Observe a man performing some automatic action, such as planing a
deal board, or cutting out a pattern, which he has done so often that
he is now able to do it “mechanically.” It is certain that his brain
co-operates, and that he could not act thus with an injured brain;
yet he is said to act unconsciously, his brain occupied elsewhere as
he whistles, talks to bystanders, or thinks of his wife and children.
Yet the brain is acting as an overseer of his work, attentive to every
stroke of the plane, every snip of the scissors; and this becomes
evident directly his attention is otherwise absorbed by an interesting
question addressed to him, or an interesting object meeting his eye:
then the work pauses, his hands are arrested, and the automatic action
will only be resumed when his attention is released--when he has
answered your question, or satisfied himself about the object.
42. This is a step towards understanding the co-operation of the brain
even in those connate reflexes which were not originally voluntary
acts, but were from the first organized tendencies, and are capable
of being realized in the absence of the brain. I admit that it is
difficult to find proof of brain co-operation here, though I think
the anatomical and physiological evidence render it highly probable.
But distinct proof to the contrary would not suffice for the Reflex
Theory--would not prove that reflex actions were insentient--unless
there had previously been proved that which seems to me contradicted
by the clearest and most massive evidence, namely, that the brain is
the sole seat of sentience. This contradictory evidence we will now
furnish.
CHAPTER III.
INDUCTIONS FROM PARTICULAR OBSERVATIONS.
43. In the last chapter we surveyed the deductive evidence, from which
the conclusion was that Reflexion necessarily involves Sensibility,
but not necessarily any one particular _mode_ of Sensibility, such
as Consciousness, Pain, Discomfort, Attention, or the reaction of
any one of the special Senses. Although each or all of these modes
may be involved in the sensorial process which determines a reflex
act, each or all may be absent. Such is the fact of observation. This
fact is interpreted on the hypothesis that Reflexion is the exclusive
property of the spinal cord, as Sensation is of the brain. When we
come to examine the evidence for this hypothesis, we find it to move
in a circle: the brain is said to be the exclusive seat of sensation,
because reflex actions can be effected after its removal; and reflex
actions are said to be insentient because they take place in the
absence of the brain.
A gentleman was one day stoutly asserting that there were no
gold-fields except in Mexico and Peru. A nugget, dug up in California,
was presented to him, as evidence against his positive assertion.
He was not in the least disconcerted. “This metal, sir, is, I own,
extremely _like_ gold; and you tell me that it passes as such in the
market, having been declared by the assayers to be undistinguishable
from the precious metal. All this I will not dispute. Nevertheless,
the metal is not gold, but _auruminium_; it cannot be gold, _because_
gold comes only from Mexico and Peru.” In vain was he informed that
the geological formation was similar in California and Peru, and the
metals similar; he had fixed in his mind the conclusion that gold
existed _only_ in Mexico and Peru: this was a law of nature; he had no
reasons to give why it should be so; but such had been the admitted
fact for many years, and from it he would not swerve. He was not fond
of new-fangled notions, which, after all, would only lead us back to
the exploded errors of the past. To accept the statement that gold was
to be found elsewhere than in Mexico and Peru, would be to return to
the opinion of the ancients, who thought there was gold in the upper
regions of Tartary!
Sensation is not tangible, assayable, like gold. We can understand,
therefore, that the very men who would make merry with the
_auruminium_, would accept easily such a phrase as “reflex action.”
The decapitated animal defends itself against injury, gets out of
the way of annoyances, cleans itself, performs many of its ordinary
actions, but is said to do these things without that Sensibility which,
if its head were on, would guide them. Even before the Reflex Theory
was invented this line of argument was used. Gall, referring to the
experiments of Sue, previously noticed, says that “Sue confounds the
effects of Irritability with those of Sensibility.”[246] Not gold, dear
sir, but _auruminium_!
44. On investigating the phenomena we soon come upon two classes which
must cause hesitation. We find that the brain has its reflex processes,
of the same order as those of the cord; we find that these processes
may be conscious or unconscious, voluntary or involuntary; so that we
can no longer separate brain from cord on the ground of Reflexion. In
this respect, at least, the two are mechanisms with similar powers.
Turning now to the other class of phenomena, we find that precisely as
the brain is an organ of Reflexion, the cord is an organ of Sensation.
All the evidence we can have, from which to infer the presence of
sensation, is furnished by the sensorial processes in the cord. Remove
the brain, and the animal still manifests Sensibility, and this in
degrees of energy and complexity proportional to the mechanisms still
intact: some of these manifestations have the character of volitional
actions, some of automatic actions, some of Memory, Judgment, and
selective Adaptation. These we observe not indeed with the energy and
variety of such manifestations when the brain co-operates, since the
disturbance of the organism which is the consequence of the brain’s
removal--or the meagreness of the organism which is the correlative
of the brain never having been developed--must of course involve a
corresponding difference in the observed phenomena; but the point here
brought forward is that phenomena of the same _order_ are manifested by
organisms with or without a brain.
45. Let us go seriatim through the evidence of these two classes:--
CEREBRAL REFLEXES.
While Theory separated the actions of the cord from those of the brain
on the ground of their being at times unconscious and involuntary,
Observation disclosed that this distinction could not be maintained.
This step was taken by Dr. Laycock in 1840. In a striking paper[247]
read by him at the British Association in 1844, he brought together the
evidence on which his view was founded. The idea has been adopted and
illustrated in the writings of Dr. Carpenter, who now calls the action
“unconscious cerebration.”
“I was led to this opinion,” Dr. Laycock says in announcing his view,
“by the general principle that the ganglia within the cranium, being
a continuation of the spinal cord, must necessarily be regulated as
to their reaction on external agencies by laws identical with those
governing the spinal ganglia and their analogues in the lower animals.
If, therefore, the spinal cord is a centre of reflexion, the brain must
also be one.” It is a matter of regret that Dr. Laycock did not extend
this principle, and declare that whatever was true of the _properties_
of the cranial centres must also be true of the spinal centres; if the
brain have Sensibility, the spinal cord must also have it.
Dr. Laycock refers to the curious phenomena of Hydrophobia in proof
that reflex actions may be excited by the optic nerves, or by a mere
idea of water. When a mirror was presented to a patient, the reflexion
of the light acting on his retina, in the manner of a reflexion
from the surface of water, produced a convulsive sobbing, as in the
attempt to swallow water, and the patient turned aside his head with
expressions of terror. Money was given him to induce him to look a
second time, but before he had looked a minute the same effect was
produced.
The _idea_ of water excited similar convulsions. No sooner was it
suggested that the patient should swallow a little water than he seemed
frightened, and began to cry out. By kindly encouragements he was
brought to express his willingness to drink, but the _sound_ of the
water, as it was poured out again, brought on convulsions. In another
case, “on our proposing to him to drink, he started up, and recovered
his breath by a deep convulsive inspiration. On being urged to try,
he took a cup of water in one hand and a spoon in the other. With as
expression of terror, yet with great resolution, he filled the spoon
and proceeded to carry it to his lips; but before it reached his mouth
his courage forsook him, and he was forced to desist. He repeatedly
renewed the attempt, but with no more success. His arm became rigid and
immovable whenever he tried to raise it to his mouth, and he struggled
in vain against this spasmodic resistance.”
In 1843 Griesinger--who appears to have known nothing of Dr. Laycock’s
paper--published his remarkably suggestive memoir on Psychical
Reflexes,[248] in which he extends the principle of Reflexion to all
the cerebro-spinal centres. The whole course of subsequent research
has confirmed this view; so that we may say with Landry, “L’existence
du pouvoir réflexe dans l’encéphale ou dans quelques unes de ses
parties établit une nouvelle analogie entre le centre nerveux cranien
et la moelle épinière.”[249] Indeed we have only to consider the
Laughter which follows a ludicrous idea, or the Terror which follows
a suggestion of danger,--the varying and involuntary expression of
Emotion,--and the curious phenomena of Imitation and Contagion,--to see
how large a place cerebral reflexion occupies.
46. The existence of cerebral reflexion having been thus made manifest,
Dr. Carpenter classed all reflex actions under three heads: 1°, the
excito-motor, determined by the spinal cord; 2°, the sensori-motor,
determined by the ganglia at the base of the brain; 3°, ideo-motor,
determined by the brain. From all these Consciousness is absent. From
the first, he supposes Sensation to be absent. As an artifice, such
a classification may have its value, but it is physiologically and
psychologically misleading. It sustains the hypothesis of an imaginary
excito-motor mechanism. It restricts Sensibility to one of its many
modes. It fails altogether to connect Sensation with Thought, the Logic
of Feeling with the Logic of Signs.
47. The view of Sensibility as common to the whole cerebro-spinal axis
is by no means new. Robert Whytt maintained it. Prochaska held that
the spinal cord formed the greater part of the _sensorium commune_;
and he adduced, in proof, the familiar facts of sensibility manifested
by headless animals. The next writer whom I can discover to have
held this opinion is J. J. Sue,--the father of the celebrated French
romance-writer,--who, in 1803, conceived that his experiments proved
the spinal cord to be capable of replacing, to a certain extent, the
functions of the brain.[250] Next came Legallois,[251] who undertook
to show, by a series of experiments, that the principle of sensation
and movement, in the trunk and extremities, has its seat in the spinal
cord. The mere division of the cord, he said, produces “the astonishing
result of an animal, in which the head and the body enjoy separate
vitality, the head living as if the body did not exist, and the body
living as if the head did not exist. Guinea-pigs, after decapitation,
seem very sensitive to the pain caused by the wound in the neck; they
alternately carry first one hind-leg and then the other, to the spot,
as if to scratch it. Kittens also do the same.”
A few years afterwards, 1817, Dr. Wilson Philip concluded that “the
spinal marrow possesses sensorial power, as appears from very simple
experiments”; but he held the brain to be the _chief_ source of
sensorial power.[252] The following year, Lallemand supported this
opinion by the very curious phenomena exhibited by infants born without
brains: these infants breathed, swallowed, sucked, squalled, and gave
very unequivocal signs of sensibility. The value of such observations
consists in disproving the objection frequently urged against the
evidence of decapitated animals, namely, that in these animals the
spinal cord preserves the remains of a sensibility endowed by the brain.
Longet here places an observation recorded by Beyer. A new-born infant,
whose brain, during the birth, had been completely extirpated (to save
the mother’s life), was wrapped in a towel, and placed in the corner
of the room, as a lifeless mass. While the surgeon was giving all his
care to the mother, he heard with horror a kind of murmur proceeding
from the spot where the body had been placed. In three minutes a
distinct _cry_ was heard. The towel was removed, and, to the surprise
of all, this brainless infant was seen struggling with rapid movement
of its arms and legs. It cried, and gave other signs of sensibility for
several minutes.[253]
In 1828 Calmeil arrived at the same conclusion as that reached by
Legallois, Wilson Philip, and Lallemand. Indeed when, in 1833, the
Reflex Theory appeared, this opinion was so firmly rooted, that
we find Mr. Grainger combating it as the established error of the
day. He takes as much pains to show that physiologists are wrong in
attributing sensation to the spinal cord, as I am here taking to show
that they were right.[254] “It is, indeed, apparent,” he says, “that
the whole question concerning the truth or falsehood of the theory
which attributes the reflex power to the spinal cord hinges upon the
correctness or incorrectness of the received doctrines respecting the
seat of sensation and volition; so that until those doctrines are
proved to be false, it is impossible to establish the hypothesis of Dr.
Hall.”[255]
The reader is requested to take note of this, because when we come to
the evidence which proves the spinal cord to be a centre of sensation,
we shall find that the _only_ ground for rejecting that evidence is the
assumed truth of the Reflex Theory, coupled with the assumption of the
brain being the exclusive seat of sensation. Whereas if the evidence
proves that the spinal cord _is_ a sensational centre, then the Reflex
Theory is destroyed, and cannot be urged against such evidence.
48. Thus many of the facts which prove the sensational function of
the spinal cord were known, and even a vague conception of their real
significance was general, until the Reflex Theory came to explain
all such facts as the results of mechanical adjustment, and of a new
nervous principle called “Reflexion.” For many years this theory has
reigned, and met with but little opposition. Yet the true doctrine has
not wanted defenders in Germany. Nasse[256] denied that decapitated
animals showed no spontaneity; he asserted that they exhibited clear
signs of mental activity. Carus sarcastically pointed out that the
_word_ “reflex” was replacing “irritability,” as a key to unlock all
puzzles; and he took up a position which is very similar to the one
occupied in these pages, namely, that the spinal cord being formed of
gray matter as well as of fibres, it must have sensibility and power of
reacting on nervous stimulus, no less than conductibility; that, in
fact, it is a centre, and must act like all other nerve-centres.[257]
J. W. Arnold opposed the Reflex Theory in a very remarkable little
work, in which he vindicates the claim of the spinal cord as a sensory
and motor centre, although denying to its actions any volitional
character.[258] This was in 1844. Eleven years elapsed without any
further opposition, when Edward Pflüger, in 1853, published his work
on the Sensorial Functions of the spinal cord.[259] In this work he
recurred to the old views of Prochaska and Legallois; but although he
attacked Marshall Hall with merciless severity, he did not point out
the fundamental error of the Reflex Theory, which theory he seems to
accept. Nor did he give his views that philosophical and anatomical
basis which could alone render his interpretations acceptable. Added to
this, the tone of asperity in which his work was written, created some
prejudice against him; and thus, while many admitted his facts, they
rejected his conclusions.[260]
In 1858 Professor Owen read a paper of mine at the Leeds meeting of
the British Association, on “The spinal cord as a centre of Sensation
and Volition,” in which a rapid indication of my point of view, and
an account of some experiments to illustrate it, were given--_not_, I
believe, conclusive to any of the audience. Indeed, the subject was
too vast to be discussed in such a paper; and my object was rather to
excite new inquiry, than to make converts to a view which could only be
embraced after a thorough reinvestigation of the dominant theories.
In 1859 appeared Schiff’s work;[261] and here we find a large space
allotted to the discussion of Pflüger’s doctrine. Schiff, whose
immense experience as an experimentalist, and whose acuteness and
caution every one will highly estimate, frankly pronounces in favor
of the sensational character of spinal actions; but he denies that
they are volitional, and objects strongly to the introduction of
any such idea as that of “psychical activity.” He thinks it utterly
untenable to suppose that impressions have reactions in the brain
which they have not in the spinal cord:--if one has sensibility, the
other must have it; and he thinks that, so far from the actions of the
cord being distinguishable from those of the brain by the character
of “reflexion,” and depending on a mechanical arrangement--_all_
actions, cerebral or spinal, are reflex; _all_ depend on a mechanical
arrangement.[262]
Since that time there has been the remarkable work of Goltz, so
often cited in these pages,[263] and his subsequent experiments on
dogs, which (although he does not decisively adopt the views of
Pflüger) furnish ample evidence that sensation and volition cannot be
exclusively localised in the brain.
49. Heubel’s interesting experiments[264] show that a frog may be
thrown into a state of profound sleep by the withdrawal of all external
stimulation, and in this state will remain lying on its back for hours.
Now this position is one so very uncomfortable that, when awake, the
frog will not retain it a moment, if free to turn round; and when
asleep, a prick on the toe, a sudden noise, or a beam of light will
awaken it, causing it to turn. That is to say, the withdrawal of the
normal stimuli so lowers the sensibility of the frog’s nerve-centres,
that he does not feel the effects of the unusual position, but feels
them directly the centres are stimulated into activity. All this is
intelligible enough on the supposition of the state of sleep being
dependent on a lowering of the cerebral activity. But what shall we
say on learning that precisely the same phenomena are manifested by a
brainless frog? Every one knows that the brainless frog is intolerant
of lying on its back, and immediately turns round, if placed on it. Yet
the brainless frog may be thrown into deep sleep by the same exclusion
of external stimuli; from which he also will be awakened by a prick,
a noise, or a beam of light; and no sooner is he awakened than he at
once turns round. Were the brainless frog incapable of sensation, a
prick on his toe would cause a simple reflex withdrawal of the leg;
but this is not the effect; on the contrary, the stimulus excites the
whole spinal cord, and whatever sensation of discomfort may be caused
by the abnormal position of the limbs in an uninjured awakened frog, is
excited in the brainless frog.
50. I need not swell this chapter with examples of Sensibility in
animals deprived of the brain; many have already been given, and
any text-book of Physiology will supply more. No one disputes the
observations, only the inference that these manifestations were
sentient: they are said to have been merely mechanical reflexes. If,
however, we can detect in them _some_ evidence of what all recognize as
peculiarly characteristic of Mind, the mechanical interpretation will
be less plausible.
At the outset the reader must be warned against exaggerating and
distorting the bearing of my remarks, and must not suppose that I
disregard the vast differences between the Logic of Signs which
belongs to Thought, and the Logic of Feeling which belongs to
Sensation, nor suppose that I look upon the spinal cord as a mental
organ having the _same_ functions as the brain. All that I wish to
establish is the common character of spinal and cerebral processes,
modified as each is by the character of the actions initiated by the
process.
51. This premised, let us begin with the evidence of
DISCRIMINATION.
Although this process is usually regarded as purely psychological, it
must obviously have its physiological side; we find it in Sensation as
in Ideation, and may expect to find it in unconscious as in conscious
processes--in a word, in all sensorial processes whatever. Place a
bit of marble on your tongue, and it will be touched, but not tasted:
the sensations of contact and temperature will excite reflexes, but
little or no reflexes from parotid and salivary glands. A difference in
sensation has a corresponding difference in reflex action; which may be
made evident by removing the tasteless marble, and replacing it by a
pinch of carbonate of lime, i. e. the marble in another state reduced
to a powder: this will excite a sensation of taste, and a secretion
from the glands. In both cases your sentient organism was affected, but
it reacted differently because the difference of the stimulation was
discriminated: consciously or unconsciously, you _felt_ differently.
Again: touch the back of your mouth with your finger, or a feather, and
a convulsive contraction of the gullet responds, followed by vomiting,
if the excitation be renewed. Yet these same nerves and muscles respond
by the totally opposite action of swallowing, if instead of the
stimulation coming from your finger, it come from the pressure of food
or drink.
Analogous experiments on animals without their brains yield similar
results.[265] The salivary secretion and the ordinary reactions of
Taste are provoked by sapid substances. Still more conclusive are the
observations made on a dog whose spinal cord has been divided, and
who therefore according to the reigning ideas is incapable of feeling
any impression made on parts below the section. A pencil inserted in
the rectum causes a reaction of the muscles energetically resisting
the entrance of this foreign body; yet this rectum so sensitive in
its reaction on the stimulus of the pencil, responds by the totally
different reaction--the relaxation of the muscles--on the stimulus of
fæcal matters.
52. “This is all mechanical,” you say? Mechanical, no doubt, as all
actions are; but the question here is whether among the conditions of
the mechanical action Sensibility has a place? The answer can only be
grounded on induction. The actions of the dog are analogous to the
actions which you know were sentient in yourself. There was in both a
discrimination, in both a corresponding reaction. I admit that what is
here called “discrimination” is the application of a logical term to a
mechanical process; I admit that if the spinal mechanism is insentient,
the fact of discrimination may still be manifested; but I conceive
that the many and coercive grounds for admitting that the mechanism is
sentient gain further support in the evidence of discrimination. Every
particular sensation has its corresponding reaction; and although this
has been acquired during ancestral or individual experiences, so that
in the majority of cases there is no consciousness accompanying the
operation, this, as we have seen, is not a valid argument against the
existence of a sensorial process. We have only to lower the Sensibility
of the cord by anæsthetics, or to _preoccupy_ its energies by some
other excitation, and the reaction fails.
MEMORY.
53. “But discrimination, if not a purely physical process, implies
Memory?” No doubt. And what is Memory--on its physiological side--but
an organized tendency to react on lines previously traversed? As
Griesinger truly says: “There is Memory in all the functions of the
central organs, including the spinal cord. There is one for reflex
actions, no less than for sense-images, words, and ideas.” Gratiolet
makes a similar assertion.[266] Indeed if, as we have seen, reflex
actions are partly connate, and partly acquired, it is obvious that the
second class must involve that very reproduction of experiences, which
in the sphere of Intellect is called Memory.
There is assuredly something paradoxical at first in this application
of the terms of the Logic of Signs, yet the psychologist will find
it of great service. But if the terms discrimination and memory
be objected to, they may be replaced by some such phrase as the
“adaptation of the mechanism to varying impulses.” On its objective
side, Discrimination is Neural Grouping; on its subjective side, it is
Association of experiences.
INSTINCT.
54. If we can detect evidences of Volition and Instinct in the
absence of the brain, our thesis may be considered less questionable.
And such evidence there is. Goltz decapitated a male frog (in the
pairing season), and observed that it not only sought, grasped, and
energetically embraced a female, but could always discriminate a
female from a male. Thus when a male frog closely resembling a female
in size and shape was presented to this decapitated animal, he clasped
it, but rapidly let it go again, whereas even the dead body of a
female was held as in a vice. Goltz tried to _delude_ this brainless
animal in various ways, always in vain. Only a female would be held
in his embrace. Goltz then presented a female in a reversed position,
so that the head was grasped by the male. Now here, had there been
simply a reflex machine, incapable of sentient discrimination, the
clutched female would have been held in this position, just like any
other object which excited the reflex; there would have been no “sense
of incongruity,” such as Goltz noticed in his frog, who at once began
a series of movements by which he was enabled, without letting the
female escape, to bring her into the proper position. To render this
observation still more significant, I may add that Goltz did not find
all male frogs act thus--many relinquished the female thus improperly
presented to them. Such phenomena observed in frogs possessing brains,
would be accepted as evidence of sexual instinct and volition.
Further: Goltz removed the brain from a frog, which he then held
under water, gently pressing the body so as to drive the air out of
its lungs; the body being then heavier than the water sank to the
bottom, where it remained motionless. He repeated this procedure with
another frog, not brainless but blinded. This one sank also, but in a
few minutes rose to the surface to breathe. This difference naturally
suggests that the brainless frog was insensible of the condition which
in the other caused a movement of relief. The one felt impending
suffocation, the other felt nothing. Such was the interpretation of a
German friend in whose presence I repeated the experiment. But I had
been instructed by Goltz, and bade my friend wait awhile. He did so,
and saw the brainless frog slowly rise to the surface and breathe there
like his blinded companion. So that the only difference observable was
in the lessened sensibility of the brainless frog.
55. But Goltz records a still more conclusive case. In a large vessel
of water he inverted a glass jar also containing water, which could
then only be retained in the jar by atmospheric pressure. Through the
neck of this inverted jar he thrust a blinded frog, not having pressed
the air out of its lungs. It rose at once in the jar, touching the
inverted bottom with its nose, and when the necessity of fresh air
was felt, the frog began restlessly feeling about the surface of its
prison till an issue was found in the neck of the jar, through which it
dashed into the vessel, and at once rose to the surface of the water
to breathe. In this observation are plainly manifested the stimulation
of uneasy sensation, the volition of seeking relief, and the
discrimination of it when found. If this frog was a sentient mechanism,
what shall we say to the fact that a brainless frog was observed to
go through precisely the same series of actions? Goltz pertinently
remarks: “So long as physiologists satisfied themselves that the
brain was the sole organ of sensation, it was easy to declare all the
actions of the brainless animal to be merely reflex. But now we must
ask whether the greater part of these actions are not due to the _power
of adaptation_ in the central organs, and are therefore to be struck
out of the class of simple reflexes? If I bind one leg of a brainless
frog and observe that he not only sees an obstacle, but crawls aside
from it, I must regard these movements as regulated by his central
power of adaptation; but now suppose I unbind the leg and remove the
obstacle, then if I prick the frog he hops forward. Must I now declare
this hop to have been a simple reflex? Not at all. In both cases the
physiological processes have been similar.”
* * * * *
56. There are no doubt readers who will dismiss all evidence drawn
from experiments on frogs, as irrelevant to mammals and man. Let us
therefore see how the evidence stands with respect to animals higher
in the scale, endowed with less questionable mental faculties. In a
former chapter (PROBLEM II. § 29) we recorded the marked results of
removing the cerebral hemispheres; and at the same time suggested that
these by no means justified the conclusion usually drawn respecting
the hemispheres as the exclusive seat of sensation. And this on two
grounds: First, because the absence of some sensitive phenomena does
not prevent the presence of others: the mutilated organism is still
capable of manifesting Sensibility in those organs which remain intact.
Secondly, because were the mutilation followed by total destruction of
Sensibility, this would not prove Sensibility in the normal organism to
have its seat in the part injured. If the removal of a pin will destroy
the chronometric action of a watch, we do not thence infer that the
chronometric action was the function of this pin. And this objection
has the greater force when we remember that one hemisphere may be
removed without the consequent loss of a single function, and both may
be removed without the loss of several functions usually ascribed to
cerebral influence.[267]
57. Consider the analogous effects of injuries to or removal of
the Cerebellum, in causing disturbance of locomotion, whence the
conclusion has been drawn that the Cerebellum is the exclusive organ
of muscular co-ordination, in spite of the unquestionable evidence
that very many muscular co-ordinations still persist after this organ
is removed. What is the part played by the Cerebellum I do not pause
here to examine.[268] I only say that the movements of swimming,
sucking, swallowing, breathing, crying, micturition, defecation,
etc., are co-ordinated as well after removal of the Cerebellum as
they were before, and that consequently _their_ co-ordination has not
its seat in the Cerebellum. The parallelism is obvious. Removal of
the Cerebrum causes a disturbance in the combination of sensations,
and the execution of certain sense-guided actions, but causes little
appreciable disturbance in others. Removal of the Cerebellum causes
a disturbance in the combination of certain muscular sensations, and
the execution of certain co-ordinated actions, with little appreciable
disturbance in others.
58. So little have the facts been surveyed and estimated in their
entirety that there is perhaps no subject on which physiologists are
more agreed than on the function of the Cerebellum being that of
co-ordination. Yet consider this decisive experiment. I etherized
three healthy frogs, from one I removed the entire cranial centres;
from another I removed only the cerebellum; and, leaving the third
in possession of an intact encephalon, I made two sections of the
posterior columns of the spinal cord. The two first hopped, swam,
used their legs in defence, and exhibited a variety of muscular
co-ordinations, although in both the supposed organ of co-ordination
was absent. Whereas the third, which had this organ intact, and
was capable of moving each limb separately, and each pair of limbs
separately, was utterly incapable of moving all four simultaneously.
Why was this? Obviously because in the first two frogs the motor
mechanism remained intact, and only the cerebral and cerebellar
influence was removed; in the third frog the sensory part of the
motor mechanism had been divided, and no combination of the limbs was
possible.
59. Physiological induction agrees with anatomical induction in
assigning to the cerebrum and cerebellum the office of _incitation_
and _regulation_ rather than of _innervation_; for, as we have seen,
no nerve issues directly from them (PROBLEM II. § 7). Consequently the
effects of injuries to these centres are losses of spontaneity and of
complexity in the manifestations. Inasmuch as in the intact organism
all sensory impressions are propagated throughout the nervous centres,
the reactions of these highest centres will enter into the complex of
every adjusted movement; so the abolition of these centres will be the
dropping of a link in the chain, the abolition of a special element
in the complex group. The organs which are still intact will react,
each in its own way, on being stimulated; but the reaction will be
without the modifying influence of the absent centres. For instance,
the retinal stimulation from a luminous impression normally calls up a
cluster of associated feelings derived originally from other senses,
and a perception of the object is associated with emotions of desire,
terror, etc., according to the past history of the organism, and its
organized reactions, due to hereditary or acquired experiences. It
is these which form the complex feeling discharged in the particular
movement of prehension, or flight. Remove the brain, and there can be
no longer _this_ cluster of associated neural groups excited; there
will be therefore no emotion, simply the visual sensation, and such a
movement as is directly associated with it. The brainless dog moans
when hurt, it does not bark at the cat which it nevertheless sees,
and avoids as a mere obstacle in its path; the cat will cry, it will
not mew. The present pain moves the vocal organs, but does not revive
associated experiences. All those combinations by which a series of
dependent actions result from a single stimulation are frustrated when
the mechanism is disturbed, so that the mutilated animal can no longer
recognize its prey or its enemy, to feed on the one and fly from the
other; no longer builds its habitation, or rears its offspring. It
can still live, feed, sleep, move, and defend itself against present
discomfort; it cannot find its food, or protect itself against
prospective discomfort. We must supply the place of its Intelligence.
We must give it the food, and protect it from injuries.
There is therefore ample evidence to show that what is specially known
as Intelligence is very imperfect after the cerebral influence has been
abolished; but this does not prove the Cerebrum to be the exclusive
seat of Intelligence, it only proves it to be an indispensable factor
in a complex of factors. Still less does it prove the Cerebrum to be
the exclusive seat of Sensation, Instinct, Volition; for these may be
manifested after its removal, although of course even these will be
impaired by the loss of one factor.
60. And here an objection must be anticipated. In spite of the
familiar experience that one mode of Sensibility may be destroyed
without involving the destruction of other modes, there is a
general belief--derived from a mistaken conception of what is really
represented by the unity of Consciousness--that Consciousness
disappears altogether when it disappears at all; and hence, since
Sensation is supposed to imply Consciousness, it also cannot be
divisible, but must vanish altogether if it vanish at all. The first
answer is that Sensation as an abstraction is neither divisible nor
indivisible; but as a generalized expression of concrete sensorial
processes it is reducible to these processes, and divisible as
they are. No one doubts that we may lose a whole class of special
sensations--sight, hearing, pain, temperature, etc.--yet retain all
the others. No one doubts that we may lose a whole class of registered
experiences--forget a language, or lose memory of places so familiar as
the streets of the small town we inhabit, or of faces so familiar as
those of friends and relatives, while the names of these streets and
friends are still remembered when the sounds are heard. Yet sensation
and intelligence are not wholly lost. The mind is still erect amid
these ruins.[269]
61. This premised, let us consider the experimental evidence. Flourens
declares that when he removed the whole of the Cerebrum from pigeons
and fowls, they lost _all_ sensation, _all_ perception, _all_ instinct,
and _all_ volition. They lived perfectly well for months after the
operation, if the food were placed in their mouths; but they never
_sought_ their food; they never _took_ it, even when their beaks were
plunged into it: they could swallow, and digest the grains; but they
had no instinct to make them seek, no volition to make them pick up
the grains. They _saw_ nothing, although the iris remained irritable;
they heard nothing; they could not smell. A state of stupor came on,
resembling that of deep sleep. All voluntary action ceased. If they
were thrown into the air, they flew; if irritated, they moved away; but
if left to themselves, they remained motionless, with the head under
the wing, as in sleep. Now, inasmuch as these effects always ensue
when the Cerebrum is removed, and _never_ when only the Cerebellum is
removed, he concludes that all instincts, volitions, and sensations
“belong exclusively to the cerebral lobes.”
But all experimenters do not agree in other points named by Flourens;
nor in the conclusions he has drawn. On the contrary, it is very
certain, and we find evidence even in Flourens himself, that all
instincts and all sensations are _not_ destroyed by the removal of the
cerebral lobes.
62. Let us hear Bouillaud on this subject.[270] He repeated the
experiment of Flourens, removing the whole of the Cerebrum from
the Brain of a fowl; and he thus records his observations: “This
fowl passes the greater part of her time asleep, but she awakes at
intervals, and _spontaneously_. When she goes to sleep, she turns her
head on one side and buries it in the feathers of the wing; when she
awakes, she shakes herself, flaps her wings, and opens her eyes. In
this respect there is no difference observable between the mutilated
and the perfect bird. She does not seem to be moved at all by the
noise made round about her, but a very slight irritation of the skin
suffices to awaken her instantaneously. When the irritation ceases,
she relapses into sleep. When awake, she is often seen to cast stupid
glances here and there, _to change her place, and walk spontaneously_.
If put into a cage, _she tries to escape_; but she comes and goes
without any purpose, or rational design. When either foot, wing,
or head is pinched, she withdraws it; when she is laid hold of, she
_struggles to escape, and screams_; but no sooner is she liberated than
she rests motionless. If severely irritated, she screams loudly; but
it is not only to express pain that she uses her voice, for it is by
no means rare to _hear her cackle and cluck a little spontaneously_;
that is to say, when no external irritation affects her. Her stupidity
is profound; she knows neither objects nor places, nor persons, and is
completely divested of memory in this respect: not only does she not
know how to seek or take food, she does not even know how to swallow it
when placed in her beak--it must be pushed to the throat. Nevertheless
her indocility, her movements, her agitation, attest that she _feels_
the presence of a strange body. Inasmuch as external objects excite in
her no idea, no desire, she pays no attention to them; but she is not
absolutely deprived of the power of attention, for if much irritated
her attention is awakened. She knows not how to escape an enemy, nor
how to defend herself. All her actions, in a word, are blind, without
reflexion, without knowledge.”
In this recital, the evidence both of _sensation_ and _instinct_ is
incontestable, to any unprejudiced mind. Bouillaud, in commenting
on his observations, remarks, that assuredly _all_ sensation was
not destroyed, since the sensibilities of touch and pain were very
manifest. Nor is it certain, he says, that the fowl heard nothing, saw
nothing. It is true that she stumbled against objects, and knew not how
to avoid them. She opened her eyes on awaking, looked about, and showed
a sensibility in the pupil to light; which, he thinks, is incompatible
with the absence of all sensation of sight
63. The experiments of Longet[271] seem decisive on this latter point.
Having removed the whole of the Cerebrum from a pigeon, he observed
that whenever he approached a light brusquely to its eyes, there was
contraction of the pupil, and even winking; but, what was still more
remarkable, “when I gave a rotatory motion to the candle, and at such
a distance that there could be no sensation of heat, the pigeon made
a similar movement with its head. These observations, renewed several
times in the presence of persons who were at my lectures, left no
doubt of the persistence of sensibility to light after removal of the
cerebral lobes.” We have only to think of the baby following with its
eyes the light moved before it, to understand the kind of impression
produced by the candle on the pigeon. Longet also declares that his
experiments prove the existence of sensations of sound, after removal
of the whole cerebrum.
64. Dr. Dalton, giving the results of numerous experiments he
performed, says that removal of the Cerebrum plunges the animal in
“a profound stupor, in which he is _almost_ entirely inattentive to
surrounding objects.... Occasionally the bird opens its eyes with a
vacant stare, stretches his neck, perhaps shakes his bill once or
twice, or smoothes down the feathers upon his shoulders, and then
relapses into his former apathetic condition. This state of immobility,
however, is _not_ accompanied by the loss of sight, of hearing, or of
ordinary sensibility. _All these functions remain, as well as that
of voluntary motion._ If a pistol be discharged behind the back of
the animal, he at once opens his eyes, moves his head half round, and
gives evident signs of having heard the report; but he immediately
becomes quiet again, and pays no further attention to it. Sight is also
retained, since the bird will sometimes fix its eye on a particular
object, and watch it for several seconds together.”[272]
While, therefore, Flourens concludes from his experiments that the
Cerebrum is the seat of _all_ sensation and all volition; and Bouillaud
concludes that it is most probably the seat of _none_; Dr. Dalton
concludes that the functions of the Cerebrum are restricted to those
usually classed as intellectual. “The animal,” he says, “is still
capable, after removal of the hemispheres, of receiving sensations
from external objects. But these sensations appear to make upon
him no lasting impression. He is incapable of connecting with his
perceptions any distinct succession of ideas. He hears, for example,
the report of a pistol, but he is not alarmed by it; for the sound,
although distinctly perceived, does not suggest any idea of danger or
injury. The memory is altogether destroyed, and the recollection of
sensations is not retained from one moment to another. The limbs and
muscles are still under the control of the will; but the will itself
is inactive, because apparently it lacks its usual mental stimulus and
direction.”[273]
Dr. Dalton reminds us how disturbance of the cerebral functions in
human beings recalls these observations on animals. “In cases of
impending apoplexy, or of softening of the cerebral substance, among
the earliest and most common phenomena is a loss or impairment of
the memory. The patient forgets the names of particular objects, or
particular persons; or he is unable to calculate numbers with his usual
facility. His mental derangement is often shown in the undue estimate
which he forms of passing events. He is no longer able to appreciate
the true relation between different objects and different phenomena.
Thus he will show an exaggerated degree of solicitude about a trivial
occurrence, and will pay no attention to other matters of importance.
As the difficulty increases, he becomes careless of the directions and
advice of his attendants, and must be watched and managed like a child
or an imbecile. After a certain period he no longer appreciates the
lapse of time, and even loses the distinction between day and night.
Finally, when the injury to the hemispheres is complete, the senses may
still remain active and impressible, while the patient is completely
deprived of intelligence and judgment.”[274]
65. Having seen how far other experimenters are from confirming the
conclusions of Flourens, let us glance at his record of observations,
and we shall find there evidence that _all_ sensation and _all_
volition cannot be localized in the Cerebrum. Speaking of a fowl whose
Cerebrum was removed the day before, he says: “She shakes her head
and feathers, sometimes even she cleans and sharpens them with her
beak; sometimes she changes the leg on which she sleeps, for, like
other birds, she sleeps habitually resting upon one leg. In all these
cases she seems like a man asleep, who, without quite waking, changes
his place, and reposes in another, from the _fatigue_ occasioned by
the previous posture: he selects one more _comfortable_, stretches
himself, yawns, shakes himself a little, and falls asleep again.... On
the third day the fowl is no longer so calm; she comes and goes, but
without motive and without an aim; and if she encounters an obstacle
on her path, she knows not how to avoid it.”[275] In his second work
he remarks of a Duck operated on in the same way: “As I mentioned last
year _à propos_ of fowls, the duck walks about oftener, and for a
longer time together, when it is fasting, than when it is fed.”
Here he observes the unmistakable evidence of feelings of Hunger,
Fatigue, and Discomfort in animals which, according to him, have lost
_all_ sensation. He also observes the operation of instinct (cleaning
the feathers), and of spontaneous activity (walking about), in animals
said to have lost _all_ instinct and _all_ volition.
66. Still more decisive are the observations recorded by other
experimenters. Leyden removed the hemispheres _and_ the ganglia at
their base from a hen; yet this hen moved about and clucked. Meissner
noticed that a pigeon whose hemispheres had been removed always uttered
its _coo_, and showed restlessness at the usual feeding-time.[276]
Voit carefully extirpated the cerebrum from some pigeons, and kept
them for many months in health. For the first few weeks they exhibited
the well-known stupor. Then they began to shake this off, open their
eyes, walk, and fly about _spontaneously_. They gave unmistakable
signs of seeing and hearing. But the chief defect was in the inability
to feed themselves, and the complete insensibility to danger. They
also manifested signs of sexual feeling with lively cooings; though
quite unable to gratify their desires.[277] Vulpian having removed
the cerebrum, optic thalami, and corpora striata from a young rabbit,
found that on pinching its tail it cried out and struggled to
escape; and a rat thus mutilated not only struggled and cried when
pinched, but manifested strong emotion. “Il est très craintif, très
impressionable; il bondit pour peu qu’on le touche; le moindre bruit le
fait tressaillir. Un certain bruit d’appel fait avec les lèvres, ou un
soufflet brusque imitant celui qu’emettent les chats en colère excitent
chez le rat une vive émotion.”[278]
67. There are several well-authenticated cases on record of children
born without a vestige of brain, and others with only a vestige, who
nevertheless manifested the ordinary signs of sensation. I will cite
but one, and it shall be one for which an illustrious physiologist,
Panizza, is the guarantee. A male infant, one of twins, who lived but
eighteen hours, during that period manifested such unquestionable signs
of Sensibility as the following: the pupils contracted under light,
sharp sounds caused flutterings, and a bitter solution when placed in
the mouth was instantly rejected. This infant had not a vestige of
cerebrum, cerebellum, or cerebral ganglia. The medulla oblongata was
normal. There were no olfactory nerves, and the optic nerves terminated
in a little mass of membrane.[279]
68. The observations of Lussana and Lemoigne are both extensive and
precise, and the conclusion at which they arrive is that the removal
of the Cerebrum is the abolition of Intelligence and Instinct, but is
not the abolition of Sensation. Whereas Rolando, and after him Renzi,
consider that only the Intelligence is abolished, the supposed loss
of Instinct being really nothing more than the loss of the directive
influence which makes the Instinct to be executed.
69. Here it becomes needful to understand
THE MECHANISM OF INSTINCT.
Were we dealing with an ordinary mechanism, and the disturbances
produced in its actions by the removal of any part, we should attribute
all observed effects to _interference with the conditions of dependent
sequence_: we should infer that the actions were imperfectly performed,
or wholly abolished, because their requisite mechanical conditions were
disturbed. Let us be equally precise in dealing with the physiological
mechanism. If we have deprived it of an organ in which certain
combinations are effected, we must expect to find all actions which
were dependent on such combinations to be now impossible; but all the
actions which are not directly dependent on these combinations may
still be possible. The actions of feeding, for example, are determined
by certain sensations, when these are present in a particular sequence,
but not otherwise; the sensation of sight does not suffice, because
the animal must not only _see_ the food, he must _perceive_ it. The
action of defence and flight are also determined by certain sensations,
but only when these are connected in a certain sequence: the brainless
animal will defend itself, or move out of the way, under the stimulus
of unpleasant sensation; but will not be moved by a _prospective_
injury, because he fails to associate it with the sight of the
threatening object. In the same way a blind man shrinks at the actual
contact of the heated poker, but does not shrink at the approach of
that poker which he does not see. We do not deny him the possession
of the so-called instinct of Self-preservation on this ground; why
deny it to the brainless animal? The brainless fish or frog swims when
placed in the water, because the sensation from the _moving_ water[280]
sets going the swimming mechanism. To call this a “swimming instinct”
may seem extravagant; yet it is as fully entitled to the name as
Self-defence is, or the Alimentary Instinct. In all three cases there
is a connate mechanism set going by appropriate feelings.
70. Since all admit that there is an Alimentary Instinct, let us see
what kind of mechanism it implies. There must be a state of feeling
called Hunger, which--combined with other feelings--determines certain
muscular adjustments in the search, recognition, capture, and finally
the swallowing of the food:--a very complex series of actions, which
lead to and sustain one another until the desire is gratified. On the
mental side there are three constituents, all indispensable: the
hunger must be felt, the food must be discriminated, the desire must
be gratified; on the physical side there are also the indispensable
arrangements of the motor mechanism. Now it is obvious that the
_entire_ mechanism of this instinct cannot be localized in the brain,
even if its mental elements are localized there; and there is reason
to believe that even the mental elements--the feelings of hunger,
discrimination, and gratification--are not exclusively localized there.
The brainless animal manifests if not the feeling of Hunger, at any
rate that feeling of discomfort which is the basis of Hunger. The
restlessness is that of a hungry animal. Now we know that some of the
Systemic Sensibility is preserved, for we see the animal breathing,
swallowing, urinating, sleeping, preening its feathers, changing its
attitude, resting on one leg after the fatigue of the other, etc. We
may therefore infer that other systemic sensations, such as Hunger and
Thirst, arise under the usual conditions.
71. We have noted an indication of Hunger; but on further observation
we discover that although the food is eaten, if brought within reach
of that portion of the feeding mechanism which is still intact, yet
the second step--the feeling of recognition--is wanting. The animal
fails to perceive the food brought under his eyes, or even placed in
his mouth; unless the back part of the mouth be touched, no swallowing
takes place. Hence the animal can no longer feed himself, and is
therefore said to have lost his instinct. But although the mechanism
of the instinct has been _disturbed_, its action is not wholly
abolished. The brain is necessary for that combination of adjustments
which normally accompany the perception of food through sight and
scent; and its absence of course frustrates such combination; but we
shall presently see that although certain sensible marks by which a
perception is guided are absent, others may still be present, and
suffice.
72. Before adducing examples let me say that we cannot legitimately
attribute the abeyance of an instinct solely to the absence of the
brain, 1°, because we observe a similar abeyance of the instinct and
frustration of perception, even when the brain is present, and the
animal is in its normal state. 2°. On the other hand, some instincts
are unmistakably manifested, and some perceptions excited, after the
brain has been removed. In fact, all that is needful is that some of
the mental elements of such perception and such instinct be preserved;
and this is the case so long as the leading element is present.
73. On the first point consider this unequivocal example. A healthy,
hungry frog may be placed in a vessel in which lie a quantity of dead
flies. He sees these flies, but sight is not enough; to him they are
only so many black spots, in which he does not recognize his food,
because the flies do not move, and the _leading element_ in his
perception of food is not a _colored_ form, but a _moving_ form. Hence
this frog, in spite of brain and an intact organism, will starve amidst
appropriate food. Whereas the frog that will not snap at motionless
flies snaps at any other small moving object, though it be not his
food. Goltz observed one incessantly snapping at the moving tentacles
of a slug which was in the vessel--as if that were possible food! Not
only the stupid frog, but the more intelligent carnivora will starve
in the presence of appropriate food which is unrecognized, because the
leading element in the recognition is absent. The cat will not eat a
dead mouse, unless she has killed it herself. Predatory animals must
capture their food--unless the scent of blood excites their alimentary
instinct. So intimately is this sensation of a moving object connected
with the predatory impulse, that the cat which is unexcited by the dead
mouse cannot resist springing on a moving ball. We need not suppose the
cat to mistake this ball for food; but we must suppose that, accustomed
to pounce upon moving food, it is unable to resist the impulse of this
leading sensation.
74. The _presence_ of the brain not sufficing, in the absence of the
leading sensation, we shall now see that the _absence_ of the brain
will not prevent the execution of the instinctive action, if the
leading sensation be present. The brainless bird sees a heap of grain,
or a pan of water, but no more recognizes them by sight alone than the
frog recognizes the dead flies; yet if the bird’s feet be placed in
the water, _this_ sensation will suffice to make him drink; if placed
amid the grain, this sensation will (sometimes) suffice to make him
feed. Lussana and Lemoigne state that their brainless pigeons ate and
drank with avidity when their feet were placed in grain and water.[281]
M. Krishaber removed the hemispheres from a pigeon, and observed that
when his beak was thrust into a heap of hempseed the head was quickly
withdrawn, whereas when the beak was plunged into water the bird drank
eagerly. Every day he was forced to feed the bird by pouring the seed
into its throat, but every day it drank when the beak was thrust into
the pan of water.[282] Brücke noticed that his brainless hen, which
made no attempt to peck at the grain under her very eyes, began pecking
if the grain were thrown on the ground with force, so as to produce a
rattling sound. The sensation of hearing was here more perfect than
that of vision, and sufficed to awaken the state of feeling necessary
to initiate the pecking movement.[283]
75. Somewhat analogous phenomena are observed in Aphasia. The patient
can see printed or written letters, and even copy them; but he cannot
read, i. e. interpret, these symbols; as the birds see the grain, but
cannot connect this sensation with others. These letters and words,
which the patient cannot interpret when _seen_, he can interpret when
_heard_; he can not only understand them when spoken, but write them
if they are dictated to him. The birds recognize the grain and water
(or act as if they did) when other sensations than those of sight
are excited. Sound is the leading element in Language, both spoken
and written. We hear the words even when we see them, but we do not
see them when we hear them. The visible symbols are accessory and
subordinate. But to the born deaf the visible symbols dominate. How one
sensation will determine a particular group of movements which cannot
be effected by any other stimulus is abundantly illustrated in disease
no less than in experiment. Here is a very luminous example: Gratiolet
had a patient for six months under his eye incapable of articulating a
single word, owing to the incoherence of her incessant utterance--she
babbled sounds, but could not group the syllables into a recognizable
word. Yet she could sing the words of any song she knew, the musical
sensations being sufficient to guide her vocal organs. “Ainsi la
mémoire, infidèle dans le cas où les mots étaient des idées, devenait
claire et précise quand les mots étaient des chansons.”[284]
76. These illustrations plainly tell how the brainless animal may
starve amid his food, failing to perceive it because the leading
sensation is not excited; and how the same animal may manifest his
feeding instinct if the mechanism be set going by a leading sensation.
We are told, indeed, that in the absence of the brain the actions are
mechanical reflexes from impressions, and not comparable with the
complex processes determined by perception. I think, however, that the
only difference is in degree of complexity: a combination of touch,
temperature, and muscular movement will be simpler than one which also
combines sight, smell, and the revived images of associated sensations.
The sight of a sheep affects the instinctive mechanism of a wolf _only_
when combined with the leading element of smell. Place a stuffed sheep
in a field, and no wolf will approach and spring on it, whereas the
blind wolf will find and capture the real sheep; and I believe that
were it practicable to remove the brain without injury to the organ of
scent and the powers of locomotion, the wolf would track and capture
the living sheep.
77. The outcome of this discussion is that the mechanism of each
instinct is the adjustment of the organs which effect the instinctive
action; and this adjustment is not simply a cerebral process, but
a complex of _many_ sensorial processes; consequently the instinct
cannot be exclusively localized in the brain, although the cerebral
process may be a very important element in the adjustment. This is
true even on the supposition that in speaking of Instinct we refer
only to the state of feeling which originates the action--separating
the psychological from the physiological aspect of the phenomenon. For
the brain _minus_ the organism is obviously incapable of feelings;
whereas the organism _minus_ the brain is obviously capable of
sensibilities adequate to determine the actions. Thus the feeling
of hunger which prompts the alimentary actions does not arise if
the animal is satiated, nor does the sexual feeling which prompts
generative actions arise when the animal is castrated; but each arises
when the organism is in a particular state. In vain will food be placed
before the satiated animal, or a female before the castrated male;
food and female are seen and recognized, but no desires are excited,
in spite of the brain and its supposed instincts. On the contrary,
when the brain is removed, the need of the organism for food is felt,
and this need determines restless movements, which are directed by
certain other sensations, and the instinctive action of feeding is
finally effected; although, of course, the removal of the brain has
so disturbed the normal mechanism of the instinct that the action is
imperfect. Renzi says that an animal deprived of its brain has lost
the intelligence which enables it to seek and seize its food, but not
the instinct, since it still has the desire for food. The following
experiment may illustrate this. Renzi wounded superficially one optic
thalamus of a frog without injuring the external margin, or optic
tract. The frog showed no appreciable loss of sight, but hopped timidly
away whenever approached. Then both thalami were divided transversely,
the optic tract still being spared. This frog remained motionless
under every threat. It manifested no alarm, and even when directly
irritated, only crawled or hopped away like a brainless frog. Sight
still so far remained that obstacles were avoided.[285] Now since this
animal’s brain was intact, and its organs of movement were capable
of responding to stimulation, how are we to explain the loss of its
instinct of self-preservation? The frog perceived no danger in a
threatening approach, yet perceived an obstacle and avoided it, getting
under it if there were room enough, crawling beside it if that was
the easier escape. Why did one vision prompt the movements of escape,
and another fail? Was it not that in the one case the normal pathway
was still open, in the other closed? We know that one injury will
destroy the perception of color without destroying that of light and
shadow; so one injury may destroy the combination of neural processes
necessary for the perception of a _danger_, without destroying those
necessary for the perception of a _hindrance_. If all actions depend
on their mechanical conditions, they must be disturbed according to
the disturbance of the conditions. Nothnagel found that after removing
the _nucleus lentiformis_ on both sides of a rabbit, leaving all the
rest of the encephalon intact, the rabbit hopped when its tail was
pinched; yet although starting at the sound when hands were loudly
clapped, did not hop as a normal rabbit does; nor although closing his
eyes when a light was brought near them, did he ever move aside. No
feeling of danger was excited by sound or sight. In striking contrast
are the phenomena manifested by a rabbit whose _corpora striata_ have
been removed: it is with difficulty made to hop by pinching its skin,
whereas noises and sights cause it to make terrified bounds.[286]
78. No sooner do we analyze the conditions of an instinct than we
see the error of regarding instincts as localized in the brain. The
cerebral process is only one factor in the product--an important
factor, no doubt, since the cerebrum is the supreme centre of
incitation and regulation; but its absence does not wholly carry
away the activity of the mechanism, sentient and motor, on which the
instincts depend, it only carries away one source of stimulation and
regulation.
79. An instinct depends on a connate mechanism. Let us glance for a
moment at a parallel case of an ordinary reflex action, also dependent
on a connate mechanism, say that of sneezing. When the inner surface
of the nose is stimulated by snuff, or other irritant, the nasal
branch of the trigeminus is excited, and the effects are first a deep
inspiration, then a closure of the respiratory orifices by the tongue,
which in turn excites a spasmodic expiration. But the same effects
are producible from quite different stimulations--namely, that of the
ciliary nerves on sudden exposure to a glare of sunshine--or of the
skin nerves on a sudden draught of cold air. Brücke remarks that there
is perhaps no spot on the surface of the body from which this reflex
may not be excited in very sensitive people. He knew a gentleman who
always sneezed when in winter he laid hold of a cold door-bell; and the
fit of sneezing was only arrested by giving him a crust of bread or
something hard to gnaw. Now just as the connate mechanism of sneezing
may be set in action by a variety of stimulations, so may the connate
mechanism of an instinct.
ACQUISITION.
80. Not only may Discrimination and Instinct be manifested in the
absence of the brain, but even the acquisition of new modes of
reaction, such as are classed under Learning through Experience.
The objection is sometimes urged that animals without their brains
only manifest single reactions on stimulation--the pinched foot
is withdrawn, and then remains motionless until again pinched.
But although the stimulation does not excite a consecutive series
of movements, because there is no cerebrum to react in successive
stimulation, this does not prove the absence of sensation in the one
movement which is excited. If my hand be lying on the table, and
something irritates it, my hand is withdrawn, and then remains as
motionless as the limb of the brainless animal, _until_ some fresh
stimulation, external or internal, moves it. Although removal of
the brain causes a manifest reduction in the variety and succession
of the movements, all experimenters are agreed that animals acquire
a certain dexterity in executing actions which they had previously
failed to carry out after removal of their brains. “There is,” says
Freusberg, “a decided improvement acquired in the reactions of the
motor centres after division of the spinal cord, not indeed in vigor,
but in delicacy. Removed from the regulating influence of the brain,
the legs acquired through practice a power of self-regulation.” Nor
is this wonderful: pathways are made easy by repetition of impulses,
and new adaptations form new adjustments. It is thus all learning is
effected--intelligent, and automatic. Nor is there any force in the
objection that the power thus acquired speedily disappears, so that if
the stimulations are effected at long intervals the reactions do not
manifest their acquired dexterity. The spinal centres forget, as the
cerebral centres forget; but they also remember, i. e. they learn.
Because an animal shows to-day none of the aptitude it acquired three
days ago, we are not to deny that it had once acquired the aptitude it
has now lost. Attempt to teach a child to read by giving it spelling
lessons of two or three minutes at intervals of two or three months,
and little will the acquisition be!
* * * * *
81. Hitherto we have been considering phenomena manifested in the
absence of the cerebral hemispheres, because it is in these that the
majority of writers place the sensorium. There are, indeed, many
authoritative writers who regard the ganglionic masses at the base of
the cerebrum, and even those of the medulla oblongata, as participating
in this sensorial property, which they refuse to the lower ganglia in
the spinal cord. I cannot follow their logic. The cerebrum is by its
position as a centre of centres, and its detachment from all direct
innervation of organs, so different from the rest of the neural axis,
that we can understand how it should be assigned a special function;
although being of the same tissue as the other ganglionic masses, it
must have the same property. And what that special function is I shall
hereafter endeavor to set forth. But that the upper region of the
spinal axis should differ so profoundly from the lower region as to
be the seat of psychical processes, while the lower region is simply
the seat of mechanical processes, is what I cannot understand, so
long as the anatomical structure and physiological properties of the
two regions are seen to be identical. The various centres innervate
various organs, and have consequently various functions. As each centre
is removed, we observe a corresponding loss of function--the organism
is truncated, but continues to manifest such functions as have still
their mechanisms intact. Let us suppose the brain or upper regions of
the cord detached from the lower regions by a section of the cord; the
animal will still live, and perform almost all its functions in the
normal way, but there will be little or no consensus between the lower
and the upper regions. Granting Sensibility to both, we must still see
that the sensation excited in one will not be felt in the other. And
this is the ground on which physiologists deny that the lower regions
have Sensibility. Without pausing here to examine this point, which
will occupy us in the next chapter, I assume that the positive evidence
of Sensibility suffices to discredit that argument; and in furtherance
of that assumption will cite an example of sensation and volition
manifested by the lower portion of the cord when separated from the
brain and upper portion.
82. The function of Urination is one which notoriously belongs to
the voluntary class, in so far as it is initiated or arrested by a
voluntary impulse, and it is one which, according to the classic
teaching, has its centre in the brain. The grounds on which this
cerebral centre is assigned are very similar to those on which other
functions are assigned to cerebral centres, namely, observation of the
suppression of the function when the pathway between certain organs and
the brain is interrupted. But the careful experiments of Goltz[287]
have demonstrated that the “centre” of Urination is not in the brain,
but in the lower region of the cord. When the cord is completely
divided, Urination is performed in the _normal_ way--not passively,
not irregularly, but with all the characters of the active regular
function. And, what is also noticeable, this function is so intimately
dependent on Sensibility that it will be arrested--like any other
function--by a sensation excited from the periphery--to be resumed when
the irritation ceases. Now this arrest from a stimulation of sensory
nerves takes place when the brain is cut off from the spinal centre,
just as when the brain is in connection with it.
The same is true of Defecation, and the still more complex functions
of Generation and Parturition. I can only refer the reader to the
very remarkable case of Goltz’s bitch with the spinal cord divided
in the lumbar region, if evidence be wanted for the performance of
complex functions so long as the spinal centres were intact. It is
true that Goltz considers these functions to have been independent
of _sensation_; but that is because he has not entirely emancipated
himself from the traditional views; for my purpose it is enough that he
admits the functions to be dependent on sensorial processes.
* * * * *
83. To sum up the evidence, we may say that observation discloses a
surprising resemblance in the manifestations of the cord and brain. In
both there are reflex processes, and processes of arrest; in both there
are actions referable to conscious and unconscious processes; in both
depression and exaltation are produced by the same drugs; in both there
are manifestations interpretable, as those of Discrimination, Logic,
Instinct, Volition, Acquisition, Memory; in both there is manifestation
of Sensibility--how then can we deny Sensation to the one if we accord
it to the other?
CHAPTER IV.
NEGATIVE INDUCTIONS.
84. I fancy some reader exclaiming: “All your reasoning, and all your
marshalled facts, are swept away by the irresistible evidence of human
patients with injured spinal cords, whose legs have manifested reflex
actions, and who nevertheless declared they had _no sensation whatever_
in them. We can never be sure of what passes in an animal; but man can
tell us whether he feels an impression, or does not feel it; and since
he tells us that he does not feel it, _cannot_, however he may _try_,
we conclude that reflex action may take place without sensation.”
As this is the one solitary fact which is held to negative the mass of
evidence, anatomical and physiological, in favor of the Sensibility of
the spinal cord, it is necessary that we should candidly examine it.
No reader will suppose that during the twenty years in which I have
advocated the doctrine expounded in this volume, I have not been fully
alive to the one fact which prevented the general acceptance of the
doctrine. From the first it has seemed to me that the fact has been
misinterpreted.
85. Certain injuries to the spinal cord destroy the connection of
the parts below the injury with the parts above it; consequently no
impression made on the limbs below the injured spot is transmitted
to the brain, nor can any cerebral incitation reach those limbs. The
patient has lost all consciousness of these limbs, and all control
over them. Hunter’s patient on being asked if he felt any pain when the
prick caused his leg to kick, answered, “No: but you see my leg does.”
This answer has been regarded as a drollery; I think it expressed
a physiological truth. For on the assumption that the whole of the
cerebro-spinal axis had one uniform _property_, corresponding with
its uniform structure, and various _functions_, corresponding with
the variety of organs it innervates, a division of this axis would
necessarily create two independent seats of Sensibility, and interrupt
the consensus of their functions. In such a case it would be absurd to
expect that the cerebral segment could be affected by, or co-operate
with, what affected the spinal segment.
Now, when a man has a diseased spinal cord, the seat of injury causes,
for the time at least, a division of the whole group of centres into
two independent groups. For all purposes of sensation and volition it
is the same as if he were cut in half; his nervous mechanism _is_ cut
in half. How then can any cerebral control be obeyed by his legs; how
can any impression on his legs be felt by his cerebrum? As well might
we expect the man whose arm has been amputated, to feel the incisions
of the scalpel, when that limb is conveyed to the dissecting-table, as
to feel by his brain impressions made upon parts wholly divorced from
organic connection with the brain.
86. But, it may be objected, this is the very point urged. The man
himself does not feel the impressions on his legs when his spine has
been injured; he is as insensible to them as to the dissection of his
amputated arm. Very true. _He_ does not feel it. But if the amputated
arm were to strike the anatomist who began its dissection, if its
fingers were to grasp the scalpel, and push it away, or with the thumb
to rub off the acid irritating one of the fingers, I do not see how
we could refuse to admit that the _arm_ felt although the _man_ did
not. And this is the case with the extremities of a man whose spine is
injured. _They_ manifest every indication of sensibility. In the frog
and pigeon the legs manifest the unmistakable control which we ascribe
to volition. It is true that the man himself, when interrogated,
declares that he feels nothing; the cerebral segment has attached to
it organs of speech and expressive features, by which _its_ sensations
can be communicated to others; whereas the spinal segment has _no_ such
means of communicating _its_ sensations; but those which it _has_, it
_employs_. You can ask the cerebral segment a question, which can be
heard, understood, and answered; this is not the case with the spinal
segment: yet if you _test_ its sensibility, the result is unequivocal.
You cannot ask an animal whether it feels, but you can test its
sensibility, and that test suffices.
87. The question we have to decide, therefore, is not whether a
patient, with an injured spine, can feel impressions on, or convey
voluntary impulses to, limbs below the seat of injury--for as respects
the nervous mechanism these limbs are separated from him, no less
than if actual amputation had taken place--the question is, whether
these separated limbs have any sensibility? And the answer seems to
me unequivocally affirmative. I assert, therefore, that if there is
ample evidence to show that the spinal centres have sensibility, when
separated from the cerebral centres, such evidence can in no respect be
weakened by the fact that a man with an injured spine is unconscious
of impressions made below the seat of injury; since such a fact
necessarily follows from the establishment of two centres: the parts
above are then not sensitive to impressions on the parts below; nor are
the parts below sensitive to impressions on the parts above; but each
segment is sensitive to its own affections.
88. Every one knows that there are animals, low down in the scale,
which may be cut in two, each half continuing to live, and each capable
of reproducing its lost segments. Would any one, seeing these separated
halves move and manifest ordinary signs of sensibility, venture to say
that the one half was a living, the other an insentient, mechanism?
And since the one half had eyes, mouth, tentacles, etc., while the
other half had none of these, would the observer be surprised that
the functions of the one differed from those of the other in these
respects? Why, then, should he not conclude the same of the two halves
of the human mechanism, when disease had divided them?
89. The man, you urge, does not feel the prick on his leg. This is
true, because “the man” here designates the seeing, hearing, tasting,
smelling, talking, thinking group of organs--to the exclusion of the
limb or limbs which are no longer in sensitive connection with this
group. When a leg is amputated “the man” remains--a truncated man,
indeed, yet still one having all the distinguishing human characters.
Yet obviously in strict language we can no longer say that the man is
the _same_ as he was. “Man” or “animal” means the complex whole; and
each anatomically separable part forms one constituent of that whole.
The medulla oblongata and spinal cord innervate certain parts; the
mesencephalon innervates others; the cerebrum rises above the whole.
If after removing one limb, then another, we continued truncating the
organism till we left only the head, should we call _that_ the man?
Clearly not. Should we even suppose that the intact brain--the supposed
seat of sensation and volition--still felt, and willed? Clearly not.
There is absolutely no evidence, however faint, of the isolated head
manifesting any sensational and volitional phenomena; whereas there
is ample evidence of the truncated spinal cord manifesting some of
these phenomena. And this is intelligible when we understand that the
nerve-centres stimulate into action the organs they innervate, but do
not by themselves play any other part.
90. “The man” then does not feel the prick on his leg, but his leg
feels it. The man has no consciousness of what takes place outside the
sphere of his sensitive mechanism; and the leg is now outside that
sphere. Consciousness--as distinguished from Sentience in general--we
have seen to be a resultant of the composition of forces co-operating
at the moment; the Sensibility of the spinal cord in the regions below
the injury cannot _now_ enter into that composition. It is detached
from the upper organs. But inasmuch as the organs it innervates are
still living and active, the functions of this detached portion are
still displayed. We have seen the dog with divided cord capable of
Urination, Defecation, Generation, etc.; its hinder legs, though not
moving in a consensus with the forelegs, yet moved independently; and
all the normal reflexes of the parts followed on stimulations. To say
that “the dog” showed no signs of Sensibility when its hinder limbs
were irritated, is identifying “the dog” with the anterior half of the
organism which was not in connection with the posterior half. It is
equally true that the posterior half showed no signs of Sensibility
when the anterior was irritated. The two halves were united by the
circulation, nutrition, etc., but disunited as to sensation and
volition.
91. Do I then suppose the separated half of an animal to feel pain and
pleasure, hope and terror? The reader who has attentively followed
the exposition will be at no loss to answer. Pain, pleasure, hope,
and terror, are special modes of Sensibility, dependent on particular
neural combinations. The organs comprised in the anterior half of the
animal furnish the main conditions for these special modes, whereas
the organs comprised in the posterior half furnish few or none of
those--they contain none of the special Senses, and they are without
the chief combining centre, the brain. But since we know that a large
amount of normal Sensation is wholly without the special characters
of pain, pleasure, hope, or terror, we need not hesitate to assign
Sensation to the spinal cord because these characters are absent.
92. All I contend for is that the spinal centres have Sensibility
of the same _order_ as the cerebral centres; and that in the normal
organism this Sensibility enters as a factor into the general
Consciousness--no one portion of the nervous system being really
independent of all the others, all co-operating in every result. Over
and over again I have had to insist that the property of Sensibility
is only the general condition of Sensation; and that each particular
sensation receives its _character_ from the organs innervated, _plus_
the reaction of the whole organism. Obviously, therefore, the peculiar
character of a sensation, or “state of consciousness,” must vary with
the variations in either of these factors. To say that every segment of
the spinal cord has Sensibility, is not saying that an excitation of
that segment will produce a particular sensation of definite character;
because for this definite character there is needed the co-operation of
all those parts of the mechanism which enter into the complex product.
* * * * *
93. And here attention must be called to a double fallacy pervading
the arguments on the other side. It is always assumed that the
reactions of an organ, or part of the organism, when separated from
the rest, are typical of their reactions when forming constituents
of the normal organism. Nothing of the kind. The movement of a
muscle or a limb separated from the body may resemble that movement
when normally effected--but only as the movements of a mechanical
bird resemble those of a living bird: the modes of production are
different. So that were we to grant the postulate of the brain
being the exclusive seat of sensation, we should still deny that an
action which was effected after removal of the brain was typical of
the action effected when the brain was present. The leg of Hunter’s
patient jerked when the skin was irritated; but this action could not
be altogether the same as the similar action in a leg united with the
rest of the sensitive mechanism. Nor is this all. The leg may have
been insensible, the spinal segment which innervated it may have been
wholly without Sensibility, and still we should have to question the
logic which extended such an inference to the very different and far
more complex actions of decapitated animals. On this ground:--The
leg is, by the hypothesis, insensible because cut off from all
connection with the sensitive mechanism. But this is not the case
with the decapitated animal: there still remain the essential parts
of a sensitive mechanism--all the chief organs are still in activity,
still manifesting their functions. Decapitation has produced a great
disturbance in the mechanism, and has removed an important centre; but
nevertheless every impression excites a connected group of centres, and
this group responds.
* * * * *
94. In conclusion, unless we adopt the opinion that
Sensation--Consciousness--Sensibility, is something not belonging to
the physiological properties of the nervous system in a vital organism
(the opinion held by spiritualists), there seems no alternative but
to adopt the opinion advocated in this volume, namely, that the
physiological properties of the nervous system are inseparable from
every segment of that system; and the functions are the manifestation
of those properties as determined by the special organs with the
co-operation of all.
FOOTNOTES
[1] WORDSWORTH.
[2] Crystals not only grow by assimilation, but even repair injuries,
with a certain superficial resemblance to the repair of animal tissues.
Thus, according to the experiments of JORDAN cited by Sir JAMES PAGET
(_Lectures on Surgical Pathology_, I. 153, and 2d ed. p. 115), an
octohedral crystal of alum, if fractured and replaced in a motherlye
will in a few days exhibit a complete restoration of the original form.
The whole crystal increases, but the increase is greatest on the broken
edge, and the octohedral form is completely renewed. (Comp. § 113.)
[3] Cited by DRYSDALE, _Life and the Equivalence of Force_, Part II. p.
149.
[4] RANKE, _Die Lebensbedingungen der Nerven_, 1868, p. 80.
[5] “Il n’y a peut être pas un seul phénomène chimique dans l’organisme
qui se fasse par les procédés de la chimie de laboratoire; en
particulier il n’y a peut être pas une oxydation qui s’accomplisse par
fixation directe d’oxygène.”--CLAUDE BERNARD.
[6] Dr. MADDEN, in his essay _On the Relation of Therapeutics to
Medicine_, 1871, p. 5, gives a remarkable illustration of what may be
called the frustration of chemical affinity effected by mechanical
conditions. “Before calico can be printed, every loose particle of
cotton must be removed from the surface in order that the colored inks
may not run. This removal is effected by passing the calico over and in
contact with a red-hot iron cylinder, and by regulating the rapidity
with which the cylinder revolves, the intense heat burns off the loose
fibres, yet does no injury to the woven cloth. In other words, the
changes in the relation of the high temperature and the cotton are
too rapid to admit of the fibre combining with the oxygen. Let the
rate of revolution be reduced but very little, and the calico would
burst into flames.” Any one who has snuffed a candle with his fingers
will understand this. Dr. Madden further instances certain fulminates
which can be detonated in contact with gun-cotton without causing it
to explode--the extreme rapidity with which the fulminates expand is
too great to enable the gun-cotton to adjust its movements to this new
motion. Precisely the same kind of thing occurs in organized matter. If
the rate of its changes be reduced below a certain point, the ordinary
chemical affinities will assert themselves.
[7] I am often reminded of the surprising movements of particles of
carbonate of lime in water which my friend Professor PREYER showed
me during a visit to Bonn. He had removed one of the concretions,
usually found in connection with nerves along the spine of old frogs,
and crushed it in water; under the microscope the seeming spontaneity
and variety of the movements of the particles was such that had we
not known their origin we should certainly have attributed them to
vitality: no infusoria could have moved with more seeming spontaneity.
It is hardly physiological to conclude that because fragments of tissue
manifest ambœbiform movements therefore they are alive (STRICKER,
art. _Die Zelle_ in his _Handbuch der Lehre von den Geweben_, 1868,
p. 7), or that the heart removed from the body is _alive_ because it
still beats. LIEBERKÜHN, _Ueber Bewegungserschsinungen der Zellen_,
1870, pp. 357–359, cites examples of such movements in undeniably dead
substances. For Life, we demand not only Movement, but Functional
Activity.
[8] TELESIUS, _De Natura Rerum_, 1586, V. 184. TELESIO might have been
saved from the mistake had he attended to what NIPHUS had said on
the point in his _Expositio subtilissima_, 1559, p. 245. Comp. also
PHILELPHUS, _Epist. Familiarum_, 1502, p. 253, _verso_.
[9] The authorities just cited are ARISTOTLE, _De Anima_, Lib.
II. c. I. KANT, _Kritik der Urtheilskraft_. MÜLLER, _Physiology_.
BEALE, _Bioplasm_, and _Introduction to Todd and Bowman’s Anatomy_.
SCHELLING, _Erster Entwurf_, and _Transcendent. Idealismus_. BICHAT,
_Recherches sur la Vie et la Mort_. STAHL, _Theoria Vera Medica_.
DUGÈS, _Physiologie Comparée_. BÉCLARD, _Anatomie Générale_. LAMARCK,
_Philosophie Zoologique_. COMTE, _Cours de Philosophie Positive_.
OWEN’S _Hunterian Lectures_, 1854. HERBERT SPENCER, _Principles of
Biology_.
[10] FLETCHER, as quoted by DRYSDALE, _Life and the Equivalence of
Force_, Part II. p. 120.
[11] ROBIN et VERDEIL, _Traité de Chimie Anatomique_, 1853.
[12] PAGET, _Lectures on Surgical Pathology_, p. 14.
[13] Comp. HAECKEL, in _Siebold und Kölliker’s Zeitschrift_, 1865, p.
342, and his _Generelle Morphologie_, 1866, I, 135, 336.
[14] In the _Archiv für mikros. Anatomie_, 1865, p. 211.
[15] Here organization is the simplest form of all--molecular organized
structure, which in the higher forms becomes tissue structure,
and organ structure. The word _structure_ properly means orderly
arrangement of different materials; and molecular structure refers
to the different proximate principles which constitute the organized
substance. Usually, however, the word _structureless_ indicates the
absence of _visible_ arrangement of the parts; a cell has structure
since it has nucleus and protoplasm.
[16] In the cell-theory established by SCHLEIDEN and SCHWANN, in 1838,
and which has formed the basis of modern histology, the cell-wall
was endowed with an importance which can no longer be upheld now
that the existence of independent organisms, and of cells, without
a trace of enveloping membrane has been abundantly observed. Cells
without walls were first described by COSTE in the _Comptes Rendus_,
1845, p. 1372. They were also described by CHARLES ROBIN in 1855,
_Dict. de la Médicine_, art. _Cellule_. But little notice was taken
until MAX SCHULTZE, in his famous essay, _Ueber Muskelkörperchen
und was man eine Zelle zu nennen habe_, which appeared in _Reichert
und Du Bois Reymond’s Archiv_, 1861,--BRUECKE, in his memoir, _Die
Elementarorganismen_, 1861,--and LIONEL BEALE, in his _Structure of the
Simple Tissues_, 1861,--all about the same time began the reform in
the cell-theory which has effected a decisive change in the classical
teaching. LEYDIG claims, and with justice, to have furnished important
data in this direction (_Vom Bau des thierischen_ _Körpers_, 1864, I.
p. 11). The student interested in this discussion should consult MAX
SCHULTZE, _Das Protoplasma der Rhizopoden und der Pflanzenzellen_,
1863; HAECKEL, _Die Radiolarien_, 1862; the controversial papers by
REICHERT, in his _Archiv_ (beginning with the Report of 1863), and MAX
SCHULTZE, in his _Archiv für mikros. Anat._, with HENLE’S judgment in
his _Jahresberichte_, and KÜLLIKER’S summing-up in the last edition of
his _Gewebelehre_. For a full yet brief history of the cell-theory see
DRYSDALE, _The Protoplasmic Theory of Life_, 1874, pp. 96–106.
[17] At the time this was written, I had some fish ova in the course
of development. Out of the same mass, and in the same vessel, all
those which were supported by weed at a depth of half an inch from
the surface, lived and developed; all those, without exception, that
were at a depth of two to four inches, perished. In ordinary parlance,
surely, nothing would be objected to in the phrase, “these ova were
all in the _same_ Medium”; the water was the same, the weed the same,
the vessel the same; yet some difference of temperature and carbonic
acid made all the difference between life and death. Another curious
fact was observed; I removed eight of these ova with active embryos,
and placed them in a large watch-glass containing a solution (one half
per cent) of bichromate of ammonia. In this acid the embryos lived
and were active fifty-seven hours, although other embryos placed in a
similar watch-glass containing pond-water, survived only forty hours.
The non-effect of the acid was probably due to the non-absorption
which nullifies the effect of certain virulent poisons when they are
swallowed; but why the fish should live longer in the acid than in the
simple water, I do not at all comprehend.
[18] AGASSIZ, _Essay on Classification_, 1859, p. 15.
[19] HAECKEL, _Generelle Morphologie_, II. 211.
[20] See on this last point RANKE, _Die Lebensbedingungen der Nerven_,
1868, p. 34.
[21] See WALDEYER, art. _Eierstock_, in STRICKER’S _Handbuch der Lehre
von den Geweben_, 1870, p. 570. “I found in a fœtus, which, in a case
of extra-uterine pregnancy, had lain thirty years in the body of its
mother, the structure of the muscles as intact as if it had been born
at its full time.”--VIRCHOW, _Cellular Pathologie_, Lect. XIV.
[22] See BEALE, _The Structure of the Simple Tissues_, 1861; the
Introd. to his edition of _Todd and Bowman’s Physiological Anatomy_,
1866; and _How to Work with the Microscope_, 4th ed., 1868; also
_Bioplasm_, 1872.
[23] “The physical property of the tissue does not depend upon this
matter, _nor is its function due to it_.”--Beale, _Introduction to Todd
and Bowman_, p. 11. That is to say, he regards even contractility and
neurility as physical, not vital facts.
[24] In turning over the pages of a work which was celebrated some
half-century ago--RUDOLPHI’S _Grundriss der Physiologie_--I was
interested to find a clear recognition of this biological principle:
“Alle Theile aller Organismen,” he says, I. 233, “sie mögen noch so
verschieden in ihrem Bau, in ihrer Mischung, und in ihrer Thätigkeit
seyn, sind ohne Ausnahme _als organisch und mithin als lebend zu
betrachten_.” In a note he adds that physiologists have considered
certain solid parts--epidermis, nail, hair, and bones--to be dead; “but
all these are organically developed, and are in direct connection with
the other parts.”
[25] VIRCHOW, _Die Cellular Pathologie_, 1860, Lect. I.
[26] BEALE, _Bioplasm_, 104.
[27] KÖLLIKER, _Gewebelehre_, 5th ed., 1867, p. 12.
[28] Nevertheless there are some facts directly contradicting his
conclusions. For example, he considers the axis cylinder of the nerve
to be formed material, and agrees with MAX SCHULTZE and others as to
its fibrillated structure; yet according to LISTER and TURNER, GERLACH
and FREY, the axis cylinder is deeply stained by carmine, and in this
respect resembles the nucleus of protoplasm.
[29] From the quite recent experiments M. BAILLON has submitted to the
_Académie des Sciences_ (15th February, 1875), it appears that although
cut flowers absorb colored fluids, the roots when intact only absorb
the fluid, and reject the coloring matters, by a veritable dialysis.
[30] GERLACH cited by RANKE, _op. cit._, p. 76.
[31] STEIN, _Der Organismus der Infusionsthierchen_, 1859, p. 76.
[32] STAHL had a profound conviction of the radical difference,
though he was not able to point out the conditions involved. See his
_Disquisitio de mechanismi et organismi vera diversitate_.
[33] M. FERNAND PAPILLON has shown that animals may be fed with food
deprived of phosphates of lime if its place is supplied with magnesia,
strontia, or alumina; they make their bones out of these as out of
lime. But no such substitution is possible in muscle, nerve, or gland;
we cannot replace the phosphate of magnesia in muscles by the phosphate
of iron, lime, or potash, as we can replace the iron of a wheel by
steel, copper, or brass.
[34] Anatomy resolves the Tissues into Organites (cells, fibres,
tubes); here its province ends, and that of Chemistry begins by
pointing out the molecular composition of the Organites.
[35] This luminous conception, though vaguely seized by PINEL, was
first definitely wrought out by BICHAT. See his _Recherches sur la Vie
et la Mort_--and especially his _Anatomie Générale_, 1812, I. p. lxx.
It was one of the most germinal conceptions of modern times.
[36] Just as there go other materials besides canvas to make a sail,
and others besides iron to make a windlass, so there go other tissues
besides the muscular to form a muscle--there is the membranous
envelope, the nerve, the blood-vessels, the lymphatics, the tendon, and
the fat. Even in Contraction there is another property involved besides
the Contractility of the muscular element, namely, the Elasticity
of the fibrous wall of the muscular tube; but Contractility is the
dominant property, and determines the speciality of the function.
[37] “L’élément musculaire peut être annexé à une foule de mécanismes
divers; tantôt à un os, tantôt à un intestin, tantôt à une vessie,
tantôt à un vaisseau, tantôt à un conduit excréteur, tantôt enfin à des
appareils tout à fait spéciaux à certaines espèces d’animaux.”--CLAUDE
BERNARD, _Rapport sur les Progrès de la Physiologie générale_, 1867, p.
38.
[38] VULPIAN, _Leçons sur la Physiologie du Système Nerveux_, 1866,
p. 581. In a work just published I find M. LUYS hesitating at the
consistent application of this law. After pointing out the identity
of the tissue in cerebrum and spinal cord, he is only prepared
to say that we cannot deny that there is _no impossibility_ in
admitting physiological equivalence where there is morphological
equivalence.--LUYS, _Actions Reflexes du Cerveau_, 1874, p. 14.
[39] It is because men converted the result into a principle, and
supposed that Life preceded the Organism, that they were led to puzzle
themselves over such facts as the continuance of vitality in divided
organisms. ARISTOTLE felt the force of the objection: “Plants when
divided are seen to live, and so are certain insects, as if still
possessing the same Vital Principle (ψυχή) considered specifically
(τῷ εἴδει) though not the same numerically (μὴ ἀριθμῷ). Each of these
parts has sensation and locomotion for a time; and there is no room for
surprise at their not continuing to manifest these properties, seeing
that the organs necessary for their preservation are absent.”--_De
Anima_, Lib. I. Ch. IV. Compare BASSO, _Philos. Naturalis adversus
Aristotelem_, Amsterdam, 1649, p. 260; and TAURELLUS, _Contra
Cæsalpinum_, 1650, p. 850; neither of them grappling with the
difficulty so firmly as ARISTOTLE.
[40] SPENCER, _Principles of Biology_, 1864, I. 153.
[41] Comp. LAMARCK, _Philos. Zool._, II. 114.
[42] Comp. SPENCER, _op. cit._, II. 362, 363, for good illustrations of
this.
[43] AGASSIZ, _Essay on Classification_, p. 91.
[44] “Nulla in corpore animali para ante aliam facta est, et omnes
simul creatæ exiatunt.”--HALLER, _Elementa Physiologiæ_, VIII. 148.
[45] QUATREFAGES, _Metamorphoses de l’Homme et des Animaux_, 1862, p.
42.
[46] VON BAER, _Ueber Entwickelungageschichte_, 1828, I. 221.
[47] Curiously enough, while the Nudibranch, which is without a shell,
possesses one during its embryonic life, there is another mollusc,
_Neritina fluviatilis_, which possessing a shell in its subsequent life
is without one during the early periods, and according to CLAPARÈDE
begins an independent existence, capable of feeding itself before it
acquires one. See his admirable memoir on the _Neritina_, in _Müller’s
Archiv_, 1857.
[48] Has any advocate of the hypothesis that animals were created as
we see them now, fully formed and wondrously adapted in all their
parts to the conditions in which they live, ever considered the hind
legs of the seal, which he may have watched in the Zoölogial Gardens?
Here is an animal which habitually swims like a fish, and cannot use
his hind limbs except as a rudder to propel him through the water; but
instead of having a fish-like tail he has two legs flattened together,
and nails on the toes--toes and nails being obvious superfluities. Now
which is the more rational interpretation, that these limbs, in spite
of their non-adaptation, were retained in rigid adherence to a Plan, or
that the limbs were inherited from an ancestor who used them as legs,
and that these legs have gradually become modified by the fish-like
habits of the seal?
[49] MILNE EDWARDS, _Intro. à la Zoologie Générale_, 1851, p. 9.
[50] VON BAER, _op. cit._, I. 203.
[51] WOLFF, _Theorie der Generation_, 1764, § 67. The reader will find
abundant and valuable corroboration of this biological principle in SIR
JAMES PAGET’S _Lectures on Surgical Pathology_.
[52] VON BAER, _Selbstbiographie_, 1866, p. 319.
[53] MILNE EDWARDS, _Intro. à la Zoologie Générale_, 176.
[54] VON BAER, _Ueber Entwickelungsgeschichte_, I. 147.
[55] LOTZE, art. _Lebenskraft_, in _Wagner’s Handwörterbuch der
Physiologie_, p. XXVI.
[56] I had kept these tritons four years in the hope that they would
breed; but in spite of their being subjected to great varieties of
treatment--for months well supplied with food, and for months reduced
almost to starvation--they never showed the slightest tendency to
breed; another among the many illustrations of the readiness with which
the generative system is affected even in very hardy and not very
impressionable animals. CLAPARÈDE observed the still more surprising
fact that the _Neritina fluviatilis_ (a river snail) not only will not
lay eggs, but will not even feed in captivity. He attributes it to the
stillness of the water in the aquarium, so unlike that of the running
streams in which the mollusc lives. See _Müller’s Archiv_, 1857.
[57] BRONN, _Morphologische Studien über die Gestaltungs-Gesetze_,
1858. Compare the note on § 11.
[58] DARWIN, _On Domestication_, II. 340. In the _Annales des
Sciences_, 1862, p. 358, M. MALM describes a fish in his collection,
the tail of which had been broken, and the bone which grew out at the
injured spot had formed a second tail with terminal fin.
[59] In the memoir on the _Anatomy and Physiology of the Nematoids_,
by Dr. CHARLTON BASTIAN, which appeared in the _Philosophical
Transactions_ for 1866, we read that even these lowly organized
worms have little power of repair. Speaking of the “paste eels”
(_Anguilulidæ_), he says, “I may state as the result of many
experiments with these that the power they possess of repairing
injuries seems very low. I have cut off portions of the posterior
extremity, and though I watched the animal for days after, could never
recognize any attempt at repair.” Perhaps, however, the season may have
some influence; and Dr. WILLIAMS’S denial respecting the Naïs may be
thus explained. [What is said above was written in 1868, and published
in the June number of the _Fortnightly Review_. In the August of that
year the question of reproduction of lost limbs was treated by Prof.
ROLLESTON in his _Address to the British Medical Association_, in which
he showed cogent evidence for the conclusion that the reproduction
of limbs only exists is animals that have feeble respiration, and
consequently slow vital processes.]
[60] This beautiful and transparent larva reminds one in many respects
of the Pike as it poises itself in the water awaiting its prey. It is
enabled to do so without the slightest exertion by the air-bladders
which it possesses in the two kidney-shaped rudiments of tracheæ, and
which in the gnat become developed into the respiratory apparatus. The
resemblance to the air-bladder of fishes is not simply that it serves
a similar purpose of sustaining the body in the water, it is in both
cases a rudiment of the respiratory apparatus, which in the fish never
becomes developed. WEISMANN calls attention to an organ in the larvæ of
certain insects (the _Culicidæ_), which have what he calls a tracheal
_gill_, which gill has this striking analogy with the fish-gill that
it separates the air from the water, and not, as a trachea, direct
from the atmosphere. See his remarkable memoir _Die nachembryonale
Entwickelung des Muscidens_, in _Siebold und Kölliker’s Zeitschrift_,
1864, p. 223.
[61] _The Variation of Animals and Plants_, 1868, II. p. 272.
[62] _Origin of Species_, 5th ed. p. 96.
[63] Mr. Darwin has himself, in the following passage, stated a
somewhat similar view, and rejected it: “In one sense the conditions of
life may be said not only to cause variability, but likewise to include
Natural Selection, for _the conditions determine whether this or that
variety shall survive_. But when man is the selecting agent, we clearly
see that the two elements of change are distinct; the conditions
cause the variability, the will of man acting either consciously or
unconsciously accumulates the variations in certain directions, and
this answers to the survival of the fittest under nature.” (p. 168.)
[64] Even in the nerve-sheaths of some Annelids there are muscles.
[65] SPENCER, _Principles of Biology_, II. 72
[66] FAIVRE, _Variabilité de l’Espèce_, p. 15.
[67] These luminous organs would furnish an interesting digression
if space permitted it. The student is referred to the chapter in
MILNE EDWARDS’S _Leçons sur la Physiologie et l’Anatomie Comparée_,
1863, VIII. 94, sq. LEYDIG, _Histologie_, 1857, p. 343. KÖLLIKER,
_Microscopical Journal_, 1858, VIII. 166, and MAX SCHULTZE, _Archiv
für mikros. Anat._, 1865, p. 124. My friend SCHULTZE was kind enough
to show me some of his preparations of the organs of _Lempyris
splendidula_, from which the drawings in his memoir were made.
They reminded me of the electric organs in fishes by a certain
faint analogy, the trachea in the one holding the position of
nerves in the other. I may remark, in passing, that it is not every
phosphorescent animal that has distinct luminous organs. There is a
lizard (_Pterodactylus Gecko_) which occasionally becomes luminous. “A
singular circumstance occurred to the colonial surgeon, who related it
to me. He was lying awake in bed when a lizard fell from the ceiling
upon the top of his mosquito-curtain; at the moment of touching it the
lizard became brilliantly luminous, illuminating the objects in the
neighborhood, much to the astonishment of the doctor.” COLLINGWOOD,
_Rambles of a Naturalist_, 1868, p. 169.
[68] MAX SCHULTZE, _Zur Kenntniss der electrischen Organe der Fische_,
1858–9.
[69] LEYDIG, _Histologie_, 1857, p. 45.
[70] OWEN, _Anatomy of The Vertebrates_, 1866, I. 358.
[71] DAVY, _Researches, Physiological and Anatomical_, 139, I. 33.
[72] “If it could be demonstrated that any complex organ existed
which could not possibly have been formed by numerous successive
slight modifications, my theory would absolutely break down.”--DARWIN,
_Origin of Species_, 5th ed. p. 227. In several passages insistence
is made on this. “Natura non facit saltum” may be perfectly true; but
without impugning the Law of Continuity we may urge that the Law of
Discontinuity is equally true. The one is an abstract ideal conception;
the other is a concrete ideal conception. According to the one, every
change from rest to motion, or from one state to another, must pass
through infinites; according to the other every change is abrupt.
In my First Series, Vol. I. p. 327, I have shown how, on mechanical
principles, every change in an organism must be abrupt. A glance at
the metamorphoses of the embryo, or the stages of insect-development,
will show very sudden and abrupt changes. Let me also cite Mr. Darwin
against himself: “When we remember such cases as the formation of
the more complex galls, and certain monstrosities, which cannot be
accounted for by reversion, cohesion, etc., and _sudden, strongly
marked deviations of structure_, such as the appearance of a moss-rose
on a common rose, we must admit that the organization of the individual
is capable through _its own laws of growth, under certain conditions_,
of undergoing great modifications, independent of the gradual
accumulation of slight inherited modifications.”--_Origin_, p. 151. See
also note to § 130, further on, p. 142.
[73] On the Nutrition of Monads, see the remarkable memoir by
CIENKOWSKI, in the _Archiv für mikros. Anatomie_, I. 221, sq.
[74] PAGET, _Lectures on Surgical Pathology_, edited by TURNER, 1865,
p. 19.
[75] It has recently been shown that certain Crustacea vary not only
from species to species, but from genus to genus, when living in
water of different degrees of saltness. By continued dilution of the
salt water an _Artemia_ was developed into another species, and this
again into a _Branchipus_--a genus of large dimensions, with an extra
abdominal segment, and a different tail; a genus, moreover, which is
propagated sexually, whereas the _Artemia_ is parthenogenetic, as a
rule. See _Nature_, 1876, June 8, p. 133.
The exceeding importance of this fact is, that it proves specific
and even generic differences to originate simply through the gradual
changes of the medium and the adaptation of the organism to these new
conditions. It also disproves the very common notion--adopted even
by Mr. DARWIN himself--that “organic beings must be exposed _during
several generations_ to new conditions to cause any appreciable amount
of variation.” Again, “Natural Selection, if it be a true principle,
will banish the belief of any great and sudden modification of
structure.”--Comp. note to § 121, p. 132.
[76] Compare LEYDIG, _Vom Bau des thierischeu Körpers_, 1864, p. 27.
[77] FERDINAND COHN, _Die contractile Gewebe im Pflanzenreich_, 1862.
By a series of numerous well-devised experiments, Cohn found that in
the stamen of the _centauria_ a tissue exists which is excitable by the
same stimula as muscle is, and which reacts like muscle, describing a
similar curve when excited, and, after reaching its maximum, relaxing.
Like the muscle it becomes fatigued by repeated contraction, and
recovers its powers by repose. Like the muscle it may be rendered
tetanic. (The researches of Dr. BURDON SANDERSON and Mr. DARWIN have
since placed beyond a doubt the Contractility and Sensibility of
certain plants.)
[78] MIVART, _The Genesis of Species_, 1871, p. 23.
[79] DOHRN, _Der Ursprung der Wirbelthiere und das Princip des
Functionswechsels_, 1875, p 74.
[80] SIGMUND MAYER, _Die peripherische Nervenzelle und die sympathische
Nervensystem_, 1876.
[81] On these cells see note to § 140.
[82] These terms designate the surface aspect of a transverse section,
of what more correctly should be called the gray columna. See Figs. 3
to 6.
[83] But this only in the higher animals. In reptiles and amphibia the
medulla descends into the cervical region, as far as the second and
third cervical vertebræ. This should be remembered in experimenting.
[84] FOSTER and BALFOUR, _Elements of Embryology_, Part I., 1874. Comp.
SCHWALBE, art. _Die Retina_, in the _Handbuch der Augenheilkunde_ of
GRAEFE _and_ SÄMISCH, 1874, I. 363.
[85] The development of the olfactory lobe and bulb is similar; it need
not be followed here.
[86] German anatomists divide this axis into trunk and crown
(_Hirnstamm_ and _Hirnmantel_). There is convenience in this division.
If we remove all the gray matter of the cerebrum, with all the white
matter radiating from it, until we again come upon gray matter--and
if we then cut the cerebellum from its descending strands of white
matter--we shall have removed the _crown_, and leave the _trunk_
remaining. This trunk is constituted by the corpora striata, nucleus
lentiformis, optic thalami, corpora quadrigemina, crura cerebri, pons,
medulla oblongata, and medulla spinalis. From this trunk all the organs
of the body are directly innervated (except those innervated from the
sympathetic?).
[87] “On s’est préoccupé du rôle spécial que pouvaient jouer les
ganglions périphériques situés dans le voisinage de certaines organes;
et on a prétendu que les nerfs ne jouissaient de leur propriété d’agir
sur ces organes qu’après avoir traversé ces ganglions. On avait admis
que l’excitation portée sur le filet nerveux avant son entré dans le
ganglion restait sans effet; que pour obtenir l’action excitatrice
des fonctions de l’organe il fallait exciter le nerf entre lui et le
ganglion voisin.”--CLAUDE BERNARD, _Systéme Nerveux_, II. 169. But on
proceeding to verify these statements by experiment, BERNARD is led to
the conclusion, “que le ganglion n’a pas d’influence propre sur le mode
de l’excitation transmise à l’organe.”
I was delighted to find my opposition to the current teaching
respecting the central functions of ganglionic cells thoroughly
borne out by the elaborate researches of SIGMUND MAYER (_Archiv für
Psychiatrie_, Bd. VI. Heft 2). Having artificially produced such cells,
he pertinently asks, How can we attribute central functions to cells
which appear in the process of regeneration of a divided nerve! The
error has its origin in the confusion of functions with properties.
[88] It is often, though incorrectly, stated that every segment of an
annulose animal has its separate ganglion. The fact is, that while the
ganglia are usually fewer than the segments, they are sometimes more
numerous.
[89] It has been proved that the cells of the cornea and the pigment
cells of the skin contract under nervous excitation. We cannot suppose
that although these are the only cells which have hitherto been brought
under experimental observation, they are the only cells subject to
nerve-influence. We may safely assume that wherever a nerve-fibre
terminates, its action will be transformed into an excitation of the
part. Habitually, however, motor-nerves are spoken of as muscle-nerves.
[90] On Deduction, see _Problems: First Series_, Vol. II. p. 159
[91] I do not here touch upon the question as to whether these actions
of the senses are _sensations_, because that question demands that
we should first settle what is _Sensation_. I may at once, however,
say that what is ordinarily understood as a sensation of _color_,
or a sensation of _sound_, is, in my opinion, not possible without
the cerebrum. But the sensibility of the eye and ear is manifestly
preserved.
[92] It has been observed that removal of the cerebellum affects the
pigment cells of the skin. No doubt other parts are also affected, but
the changes have hitherto escaped observation.
[93] OWSJANNIKOW describes the results of removing carefully the
cranial ganglia of the crayfish; and these effects MEYER observes to
be identical with those which follow removal of the large claw of
the crayfish! A. B. MEYER, _Das Hemmungsnerven-system des Herzens_,
1869, p. 23. Let me add that the phenomena described by M. FAIVRE
as following the destruction of one subœsophageal ganglion in the
_Dytiscus_, are so little to be referred to the mere absence of the
ganglion, that I find them not to occur when the whole head is removed.
[94] PFLÜGER, _Die Sensorischen Funktionen des Rückenmarks_,1858.
AUERBACH, _Günzburg’s Zeitschrift_. Jahrgang IV. p. 486. LEWES, _Leeds
Meeting of British Association_, 1858, and _Physiology of Common Life_,
1860.
This recognition of sensation, and even of volition, in spinal actions
may be found in the writings of WHYTT, UNZER, PROCHASKA, LEGALLOIS, and
MAYO; but the establishment of the Reflex Theory had displaced it, and
its revival dates from PFLÜGER.
[95] FRIEDLÄNDER (_Versuch über die innern Sinne_, 1826, I.
77) declares it to be a rational necessity: “Die Annahme eines
Nervenfluidums ist Nothwendigkeit der Vernunft.”
[96] These terms and the conception they embody were proposed by me in
1859 in a paper “On the necessity of a reform in Nerve-physiology,”
read at the Aberdeen meeting of the British Association, and were
reproduced in the _Physiology of Common Life_. (Prof. OWEN, probably
in forgetfulness of my suggestion, proposed “neuricity.” _Lectures
on the Comp. Anat. of Vertebrates_, 1866, I. p. 318.) The terms were
fortunate enough to meet with acceptance from some physiologists
both in England and France; and the conception has been more widely
accepted than the terms. The most distinguished approver was Prof.
VULPIAN. “Faute d’une meilleure détermination on peut, avec M. Lewes,
donner à la propriété physiologique des fibres nerveuses le nom de
_neurilité_; c’est là ce qui correspondra à la oontractilitè des fibres
musculaires.” _Leçons sur la physiologie du système nerveux_, 1866, p.
220. He also adopted my suggestion (since modified) of Sensibility as
the property of ganglionic cells. Compare also GAVARRET, _Phénomènes
physiques de la Vie_, 1869, pp. 213 and 222. TAULE, _Notions sur la
nature de la matière organisée_, 1866, p. 131. CHARLES ROBIN, _Anatomie
et physiologie cellulaires_, 1873, p. 166.
By these channels, and by the German, Italian, Russian, Polish, and
Hungarian translations of my work, the suggestions were carried over
Europe, crept into scientific journals, and became known to writers who
never heard of me. I only mention these facts lest the reader should
suppose that my views had been anticipated by certain continental
writers.
[97] “La force nerveuse n’existe pas comme puissance independant des
propriétés de tissu. Elle consiste en l’action des parties excités, sur
les parties excitables, l’état de l’excitation des premières agissant
comme impression ou stimulation sur les secondes.”--LANDRY, _Traité des
Paralysies_, 1859, I. 142.
[98] “Le système nerveux est tout à la fois l’origine des sensations
et l’origine des mouvements. Mais est-ce par une propriété unique, ou
par deux propriétés diverses qu’il détermine deux phénomènes aussi
distincts!” FLOURENS, _Recherches sur les propriétés et les fonctions
du Système Nerveux_, 1824, p. 1. He concludes that “la puissance
nerveuse n’est pas unique; il n’y a pas une seule propriété, il y en a
deux,” p. 24. In this he has been generally followed.
[99] “I have raised and stretched the thick orbital nerve of horses
on the handle of a scalpel, like a string on the bridge of a violin,
without exciting the least sensation; but as soon as mechanical or
chemical irritation had given rise to inflammation of the nerve a
gentle touch caused violent pain.”--ROMBERG, _Nervous Diseases_
(translated for the Sydenham Society), I. 10.
[100] The experiments of HALLER, _Sur la nature sensible et irritable
des parties_, I. 245; and the remarks of PROCHASKA, DE FUNCTIONIBUS
SYSTEMATIS NERVOSI (translated by LAYCOCK in the volume published by
the _Sydenham Society_, p. 396), ought to have sufficed. See further
on, Chap. V.
[101] In mammals about three days, in birds four days, in frogs
fourteen to twenty days.
[102] RUTHERFORD, in _Journal of Anatomy_, 1873, No. VIII. p. 331.
(FLEISCHL denies that the nerve _in situ_ has different degrees of
reaction. _Sitzungsberichte der Wiener Akad._, December, 1876.)
[103] MUNK, in the _Archiv für Anat._, 1860, p. 798.
[104] HALLER, _Mémoires sur la nature sensible et irritable des
parties_.
[105] _Comptes Rendus_, 1862, LIV. p. 965.
[106] “J’espère vous convaincre que tous les éléments anatomiques
des nerfs sensitifs, moteurs, vasomoteurs, et autres, ont les
mêmes propriétés, et ne sont distincts que par leurs fonctions.
Cette question est de la plus haute importance pour la physiologie
générale. C’est celle qui domine toute la physiologie des fibres
nerveuses.”--VULPIAN, _Leçons sur la Physiologie du Système Nerveux_,
p. 11.
[107] Mr. JAMES ANDREWS.
[108] In the second number of _La Revue Philosophique_, Paris, 1876, I
have treated this question of specific energies more at length than I
could find space for in the present volume.
[109] In 1859 I mentioned that if the nerves of a frog’s back be
exposed by raising the skin, they may be pricked or even cut without
sensible effect, although a slight prick on the skin will excite the
nerves, and cause a reflex action. In 1870, Prof. FICK expressed his
astonishment at finding that after he had cut out a piece of the
skin, leaving it attached to the body by a single nerve, electrical
stimulation of this excised skin caused the frog to make the reflex
movement of rubbing the irritated surface; whereas electrical
stimulation of the nerve-trunk itself produced no reflex effect, only a
twitching of a muscle. _Pflüger’s Archiv_, 1870, p. 327. BROWN SÉQUARD
tries to establish a distinct species of nerves as _conductors_ of
sensitive impressions, from those which are _impressionable_. The
facts on which he founds these two properties simply show that nerves
are so disposed that the stimulus which excites them in one place
fails in another. He could hardly maintain that a skin nerve contained
impressionable fibres at its periphery, and only conducting fibres in
its trunk! See his communication to the Royal Society, _Proceedings_,
1856; and _Lectures_ in the _Lancet_, 10th July, 1858.
[110] In consequence of this observation some physiologists have
maintained that Feeling or Consciousness never arises in cerebral
activity, unless the thalami and the connected tracts are at the
same time in action. I go further, and maintain that there is no
Consciousness (in the restricted meaning of the term) _unless the whole
organism is involved_. Cerebral or spinal activity will be activity of
Sensibility; but this is only the basis of Consciousness.
[111] “An unconscious sensation, which Lewes distinguishes
from perception, is to me an inconceivable (ist für mich
ein Unding).”--SCHRÖDER VAN DER KOLK, _Die Pathologie des
Geistes-Krankheiten_, p. 22.
[112] By selective adaptation is meant the varying combination of motor
impulses to suit the varying requirements of the effect to be produced.
Physical mechanisms are limited to the performance of definite actions;
sensitive mechanisms employ fluctuating combinations of elements in
response to fluctuations of stimuli. The wheels, levers, springs, and
valves of a machine cannot be differently combined according to varying
degrees of the motor-force, as the nerves and muscles of an organism
are differently combined by varying sensations. An automaton may be
constructed to play on the violin, but it will only play the air to
which it is _set_; it cannot vary the performance,--cannot play a false
note, or throw in a _crescendo_ here, a _largo_ there, according to a
caprice of feeling. We must admit that violinist has his delicate and
changing movements guided by sensations, auditory and muscular; any
interruption in the sensations would arrest the movements, which in
truth _incorporate_ them. And yet it is well known that the violinist
may perform while completely “unconscious.” I do not simply refer to
the fact that his thoughts and attention may be elsewhere; I refer to
such facts as are recorded in Pathology. TROUSSEAU, for example, had an
epileptic patient who was occasionally seized with attacks of complete
unconsciousness while he was performing in the orchestra; yet, on
reawakening to consciousness, he found that he had continued to play,
had kept proper time, and played the proper notes.
[113] CLAUDE BERNARD, _Système Nerveux_, 1858, I. 349.
[114] WORDSWORTH, _The Prelude_.
[115] “On peut dire que toujours un phénomène de mouvement reconnait
pour point de départ une impression sensitive.”--CLAUDE BERNARD, I. 267.
[116] Since this was written Prof. MICHAEL FOSTER and Mr. DEW SMITH
have published their very important researches on the motions of the
heart, which establish beyond a doubt that, in the molluscs at least,
there is no co-operation of either centre or nerve.--_Proceedings of
the Royal Society_, 18th March, 1875. (_See also Studies from the
Physiological Laboratory of Cambridge_, Part II., 1876.) Mr. Foster
knows that I had independently, and from a totally different line
of research, arrived at the same conclusion respecting the heart’s
movement.
[117] _Comptes Rendus de la Socíété de Biologie_, 1847, I. 40. In
1856 he showed that not only were the muscles of the iris directly
stimulated by light (and this not by its calorific or chemical rays),
but that sixteen days after removal of the eye from the orbit, this
effect was observable in the eel. Yet a very few days after extirpation
of the eye the nerves are disintegrated.--_Proceedings of the Royal
Society_, 1856, p. 234.
DONDERS has the following observations: “The movements of the iris
are of two kinds--reflex and voluntary. Reflex action is exhibited as
constriction of the pupil in consequence of the stimulus of incident
light upon the retina. Fontana has shown that the light falling upon
the iris produces no remarkable contraction. We have confirmed this
result by causing the image of a small distant light to fall, by means
of a convex lens, upon the iris, whereby, during slight perception of
light, a doubtful contraction occurred, which gave way to a strong
contraction so soon as the light entering the pupil excited a vivid
perception. Nevertheless, the experiments of Harless and Budge have
shown that even after death, so long as irritability remains, the pupil
still contracts upon the continued action of light. Of the correctness
of this we have satisfied ourselves. In a dog killed by loss of blood
the one eye was closed, the other opened and turned to the light: after
the lapse of an hour, the pupil of the opened eye was perceptibly
smaller than that of the closed eye. The latter now remained also
exposed to the light, and on the following day the diameter of both
eyes was equal. The upper jaw, alone with the eyes, was taken out of
some frogs; one eye was exposed to the light, while the other was
covered with a closely folded piece of black paper: after the lapse of
half an hour the pupil turned to the light was narrow, the other wide.
But the latter also contracted almost immediately after the removal of
the paper.”--DONDERS, _On the Anomalies of Accommodation and Refraction
of the Eye_. Trans. of the New Sydenham Society, p. 572.
[118] The experiment often fails, but I have seen it several times
succeed.
[119] _Pflüger’s Archiv_, 1872, p. 618.
[120] See his Researches in _Pflüger’s Archiv, Bde._ II. and IV.
[121] D’ORBIGNY, _Des Mollusques Vívants et fossils_, p. 113.
[122] _Seaside Studies_, 2d ed., p. 101.
[123] Cited by BROWN SÉQUARD, _Journal de la Physiologie_, 1858, p. 359.
[124] Dr. NORRIS has recorded some striking observations in his paper
on “Muscular Irritability” in the _Journal of Anatomy_, 1867, No. II.
p. 217. Here is the only one I can find room for: “On taking up the
_dead_ frog and touching the limb (which during life had been paralysed
by section of its nerve) with my finger, _it was suddenly shot out
as if alive_. I placed the body down, and one or two _apparently
spontaneous movements_ of small extent afterwards occurred. On touching
the skin gently with the point of a needle, by the slight pressure upon
the muscle beneath, movements of the limb were also induced, but this
high degree of exaltation very rapidly disappeared.”
[125] See their papers in the _Archiv für Psychiatrie_, 1875, Bd. V.
Heft 3.
[126] This latter statement will be justified when I come to expound
the Triple Process, which I have named the _Psychological Spectrum_.
[127] FOSTER and BALFOUR, _Elements of Embryology_, 1874, Part I. p.
52. HIS, _Untersuchungen über die erste Anlage des Wirbelthierleibes_,
1868, p. 197.
[128] They state that the cells of the epiblast are the results
of direct segmentation, whereas the cells of the other layers are
formed at a subsequent period, and are only indirectly results of
segmentation. But if the observations of KOWALEWSKY are exact, this is
not the case with the hypoblast of the Amphioxus, which is from the
first identical with the epiblast.
[129] KÖLLIKER, _Entwicklungsgeschichte des Menschen und der höheren
Thiere_, 1861, p. 71.
[130] [According to BALFOUR’S recent observations, a large part of the
muscular tissue is derived from the layer of the mesoblast belonging to
the hypoblast.]
[131] HIS, _Untersuchungen_, pp. 39, 40.
[132] Quite recently OWSJANNIKOW has pointed out the termination of
fibres in the phosphorescent cells of the _Lampyris Noctiluca_. See his
paper in the _Mémoires de l’Acad. de St. Petersbourg_, 1868, XI. 17.
These phosphorescent cells are said to be ganglion-cells by PANCERI,
_Intorno della luce che emana dalle celleule nervose_ (Rendiconto della
Accad. delle Scienze, April, 1872); and by EIMER, _Archiv für mikros.
Anatomie_, 1872, p. 653. KÖLLIKER also calls the phosphorescent organ a
nervous organ. This is not to be interpreted as meaning that neurility
is phosphorescence, but simply that in some nerve-cells there is
phosphorescent matter, which is called into activity by stimulus of the
nerves.
[133] BIDDER und KUPFFER, _Textur des Rückenmarks_, 1857, p. 108.
[What is said in the text has been rendered doubtful by the recent
researches of Mr. F. BALFOUR, _On the Development of the Spinal Nerves
in Elasmobranch Fishes_ (_Philos. Trans._, Vol. CLXVI. Part I.), which
show that in these fishes the ganglion has its origin in the spinal
cord.]
[134] Comp. PROBLEM I. § 130, with the remarks of CHARLES ROBIN,
_Anatomie et Physiologie Cellulaires_, 1873, p. 20.
[135] KLEINENBERG, _Hydra; Eine Anatomisch-Entwickelungs-Untersuchung_,
1872, p. 11. EIMER, _Zoologische Studien auf Capri_, 1873, p. 66.
A similar formation is described by Dr. ALLMAN in the _Myriothela_; he
says, however, that he has never been able to trace a direct continuity
of the caudal processes of the cells with muscular fibrils. He believes
that the processes make their way to the muscular layer through
undifferentiated protoplasm.--_Philos. Transactions_, Vol. CLXV. Part
II. p. 554.
An intermediate stage between this neuro-muscular tissue and the two
differentiated tissues seems presented in the Nematoid worms which
have muscles that send off processes into which the nerves pass.
GEGENBAUR declares his inability to decide whether these processes are
muscles or nerves. BÜTSCHLI thinks the nerve-process blends with the
muscle-process.--_Archiv für mikros. Anatomie_, 1873, p. 89.
[136] “The gray matter of the cord seems undoubtedly to be formed by a
metamorphosis of the external cells of the epiblast of the neural tube,
and is directly continuous with the epithelium; there being no strong
line of demarcation between them.”--_Op. cit._, p. 185.
[137] ROBIN, _Anat. et Physiol. Cellulaires_, p. 332.
[138] STILLING, _Bau der Nervenprimitiv-Fasern_, 1856, p. 16.
[139] “There was a time,” says KÖLLIKER, “when I confidently believed
that an hypothetical explanation of the arrangement of elements in
the spinal cord could be grounded on a basis of fact; but the deeper
my insight into the minute anatomy, the less my confidence became;
and now I am persuaded that the time is not yet come to frame such an
hypothesis.”--_Gewebelehre_, 5te Auf. 1867.
[140] In the Gasteropoda the cells range from 220 μ to 3 μ (μ = 0,001
millimètre).
[141] HAECKEL, _Müller’s Archiv_, 1857. LEYDIG, _Vom Bau des
thierischen Körpers_, 1864, I. 84. ROBIN, _Anat. et Physiol.
Cellulaires_, p. 89. Should the observations of HEITZMANN be
confirmed, there would be ground for believing that neurine is
normally fibrillated. He says that the living protoplasm in the
Amœba, white blood-corpuscle, etc., is an excessively fine network,
which condenses into granules at each contraction. (Cited in the
_Jahresberichte über Anat. und Physiol._, 1873, Bd. II.) WALTHER, who
examined frozen brains, describes the cells as quite transparent at
first, with very rare granules, but gradually while under observation
the granules became more numerous. _Centralblatt_, 1868, p. 459.
According to MAUTHNER, _Beiträge zur Kenntniss der morphologischen
Elemente des Nervensystems_, 1862, p. 41, neurine has three cardinal
forms--transparent, finely granular, and coarsely granular.
[142] TRINCHESE, _Struttura del sistema nervoso dei Cefalopodi_,
Florence, 1868, p. 7.
[143] An eminent friend of mine was one day insisting to me that the
physiological postulate made it _impossible_ for a nerve-cell to be
without its ingoing and outgoing fibres; and he was not a little
astounded when I replied, “Come into my workroom and I will show you a
thousand.”
[144] EICHHORST in _Virchow’s Archiv_, 1875, LXIV. p. 432.
[145] AUERBACH (_Ueber einen Plexus Myentericus_, 1862) describes
the ganglia as filled with apolar cells, among which only a few are
unipolar. STIEDA (_Centralnervensystem der Vögel_, 1868) finds both
apolar and unipolar cells in the spinal ganglia of birds. AXMANN (_De
Gangliorum Systematis Structura penitiori_, 1847) says the spinal cells
are all unipolar. SCHWALBE (_Archiv für mikros. Anat._, 1868) and
COURVOISIER (_ibid._, 1869) say the same. So also RANVIER, _Comptes
Rendus_, 1875. KÖLLIKER (_Gewebelehre_) speaks decidedly in favor of
both apolar and unipolar cells, but thinks the apolar are embryonic.
PAGLIANI (_Saggio sullo Stato attuale delle Cognizioni della Fisiologia
intorno al Sistema nervoso_, 1873), who represents the views of
MOLESCHOTT, admits the existence of apolar and unipolar cells. The
authors just cited are those I happen to have before me during the
rewriting of this chapter, and the list might easily be extended if
needful. AUERBACH, BIDDER, and SCHWEIGGER-SEIDEL describe unipolar
cells which in some places present the aspect of bipolar cells simply
because two cells lie together, their single poles having opposite
directions. I will add that the bipolar cells do not really render the
physiological interpretation a whit more easy than the unipolar, for
they are simply cells which form enlargements in the course of the
nerve-fibres.
[146] When Dr. BEALE says “that it is probable no nerve-cell exists
which has only _one single fibre_ connected with it” (_Bioplasm_, p.
186), he has no doubt this in his mind; since he would not, I presume,
deny that there are cells each with a single _process_.
[147] DEITERS, _Untersuchungen über Gehirn und Rückenmark_, 1865.
[148] _Archiv für mikros. Anat._, 1869, p. 217. Compere also BUTZKE,
_Archiv für Psychiatrie_, 1872, p. 584.
[149] HENLE, _Nervenlehre_, 1871, p. 58, Fig. 21.
[150] When men of such experience and skill as KÖLLIKER, BIDDER, GOLL,
and LOCKHART CLARKE declare that they have never seen a cell-process
pass directly into a dark-bordered fibre in the anterior root, what
are we to say to such figures and descriptions as those given in the
works of SCHRÖDER VAN DER KOLK, GRATIOLET, and LUYS? Even did such
arrangements exist, no transverse nor longitudinal section could
display them, owing to the different planes at which the fibres enter,
and the length and irregularity of their course.
[151] Long after the text was written, WILLIGK published in _Virchow’s
Archiv_, 1875, LXIV. p. 163, observations of anastomoses which even
KÖLLIKER admitted to be undeniable. Yet out of sixty-four preparations,
amid hundreds of cells, he could only reckon seven cases of conjunction.
[152] See the history given in STILLING’S learned work, _Ueber den Bau
der Nervenprimitiv-Faser_, p. 34; and compare MAX SHULTZE, _De Retinæ
Structura_, p. 8, and _Bau der Nasenschleimhaut_, p. 66; WALDEYER, in
the _Zeitschrift für rat. Med._, 1863; LISTER and TURNER, _Observations
on the Structure of Nerve-Fibres_, in _Quarterly Micros. Journal_,
1859; RANVIER, in the _Archives de Physiologie_, 1872.
[153] _Virchow’s Archiv_, Bd. LXXII. p. 193.
[154] _Monthly Journal of Micros. Science_, 1874, XI. p. 214.
[155] BABUCHIN, _Centralblatt_, 1868, p. 756.
[156] Even so eminent an authority as W. KRAUSE holds this both with
regard to the varicose aspect and the double contour: _Handbuch der
menschlichen Anatomie_, 1876, I. 367. BUTSCHLI, however, describes the
nerves in a living Nematode as varicose: _Archiv für Anat._, 1873, p.
78; and I have somewhere met with an observation of the double contour
being visible in the living animal.
[157] BUTZKE, _Archiv für Psychiatrie_, 1872, p. 594, states that the
granular substance has the chemical composition of myeline. If this
be so, we may suppose the “fibrils of crystallization” to represent
the coagulation of the substance which is in solution amid the myeline
granules, and corresponds with the axis cylinder of a fibre. I may
remark that in almost every good preparation nerve-cells will be found
in which, while one process is distinctly granular, another is striated
or even fibrillated.
[158] BOLL, _Die Histiologie und Histiogenese der nervösen
Centralorgane_, in the _Archiv für Psychiatrie_, 1873, p. 47.
[159] STIEDA, _Studien über das Centralnervensystem der Vögel_, 1868,
p. 65. MAUTHNER, _Op. cit._, p. 4.
[160] TURNER and LISTER, _Op. cit._, p. 8.
[161] BLESSIG, _De Retinæ Structura_, 1857.
[162] LUYS, _Recherches sur le Système nerveux_, 1865, p. 267. In a
recent and remarkable treatise the student is informed that “plus
une cellule est chargée d’un rôle purement mécanique plus elle est
volumineuse; plus l’acte qu’elle produit tend à revêtir un caractère
psychique plus elle est petite”; to move a limb the _agitation_ of
the cerebral cells must _materialize itself_ more and more, “Il a
besoin de passer par des cellules, de moins en moins spirituelles et
de plus en plus matérielles.... De même pour les cellules sensitives.
L’impression extérieure va en se modifiant, en se spiritualisant, de la
périphérie au centre.... Un phénomène de l’ordre spirituel ne sanrait
devenir sans transition un phénomène d’ordre physique.” And what is
this marvellous transition between spiritual and physical? It is the
action of medium-sized cells which “travaillent la vibration reçue, la
modifient de façon à lui ôter de son spiritualisme et à la rapprocher
davantage des ébranlements physiques.” I will not name the estimable
author, because he is simply restating what many others implicitly or
explicitly teach; but I will only ask the reader to try and realize in
thought the process thus described.
[163] SCHRÖDER VAN DER KOLK, _Pathologie der Geisteskrankheiten_, 1863,
p. 69.
[164] WUNDT, _Physiologische Psychologie_, p. 261. In his _Mechanik
der Nerven, 2 Abth._ (published just as this sheet is going to press),
he shows that a stimulus is both retarded and weakened in its passage
through a ganglion.
[165] TRINCHESE also says that the fibres “provengono dalle cellule e
_non son altro che i loro prolungamenti o poli_.”--_Op. cit._, p. 13.
An unequivocal example is seen in the _Torpedo_, where the large cells
have each their prolongation continuing without interruption into the
electrical organ. See the figure given by REICHENHEIM in the _Archiv
für Anat._, 1873, Heft VI.
[166] GOLGI, _Sulla struttura della sostanza grizia del Cervello_.
ARNDT, _Archiv für mikros. Anat._ 1870, p. 176. RINDFLEISCH also traces
these processes into the neuroglia (_ibid._, 1872, p. 453). “Deiters,
Boddaert, and other observers have stated that one dark-bordered
nerve-fibre enters each cell.... My own observations lead me to
conclude that _all_ the fibres are composed of the same material, but
that one fibre does not divide until it has passed some distance from
the cell, while others give off branches much closer to it.”--BEALE,
_Bioplasm_, p. 189.
[167] BEALE, _Bioplasm_, p. 177. MAX SCHULTZE, in _Stricker’s
Handbuch_, p. 134. Comp. STILLING, _Nervenprimitiv-Faser_, p. 133.
ARNDT, _Archiv_ _für mikros. Anat._, 1868, p. 512; and 1869, p. 237.
Weighty as these authorities are, their view is questionable--firstly,
because the forms of these cells are too constant and definite in
particular places to result from the union of fibrils coming from
various origins; but secondly, and mainly, because the teaching of
Development is opposed to it.
[168] ROBIN, _Anat. et Physiol. Cellulaires_, p. 335.
[169] _Archives de Physiologie_, 1872, p. 268.
[170] The fact of the existence of cells in the white substance is one
which is very difficult of interpretation on the current hypotheses.
The cells are found in regular columns and irregularly scattered.
BOLL thinks that while in the white substance of both cerebrum and
cerebellum there are true nerve-cells as well as connective corpuscles,
in the cord there are only the latter. But hitherto there has been
no decisive test by which a nerve-cell can be distinguished from a
connective corpuscle.
[171] _Monthly Journal of Micros. Science_, XI. 219. This accords
with what KUPFFER says respecting the entire absence of cells
in the earliest stages observed by him in the sheep. The white
substance of the spinal cord he describes as soft, transparent, and
gelatinous, in which dark points are visible; these dark points are
seen in longitudinal sections to arise from the fibrillation of the
substance.--BIDDER und KUPFFER, _Op. cit._, p. 111.
[172] WEISMANN, _Die nachembryonale Entwick. der Musciden_, in the
_Zeitschrift für Wissen. Zoologie_, 1864, Bd. XIV. Heft III.
[173] The suggestion in the text has since received a striking
confirmation in the observations of SIGMUND MAYER on the regeneration
of nerves. The nerve when divided rapidly undergoes fatty degeneration,
which is succeeded by a transformation of the myeline and axis cylinder
into a homogeneous mass; in this resolved pulp new longitudinal
lines of division appear, which subsequently become new fibres,
and new nuclei are developed in the remains of the untransformed
substance.--_Archiv für Psychiatrie_, Bd. VI. Heft II.
[174] Strong confirmation of various statements in the text, since
they were written, has been furnished by the researches of EICHHORST,
published in _Virchow’s Archiv_, LXIV. Our knowledge of the development
of nerve-tissue in human embryos is so scanty that these researches
have a great value. EICHHORST describes the striation of the cells in
the cord to begin only at the fourth month; up to this time they are,
what I find most invertebrate cells to be, granular, not fibrillar.
There is very slight branching of the cell processes until the ninth or
tenth month, when the multipolar aspect first appears; the cells are
unipolar up to the end of the fourth month. The connection between the
white columns and the gray columns is very loose up to the fifth month;
and the two are easily separated. Subsequently the union is closer.
The substance of the white columns readily separates into bundles and
fibres, but that of the gray columns falls into a granular detritus if
attempted to be teased out with needles. But after the fifth month this
is no longer so. Instead of a granular detritus there appears a network
of fine fibres and fibrils. Although the white posterior columns are
developed before the fifth month, not a single cell can be seen in
the posterior gray columns until the second half of the ninth month.
(Yet the fibres are imagined to arise in the cells!) The passage from
the granular to the fibrillar state is the same in the cell substance
and the neuroglia. The nerve-fibre, as distinguished from a naked
axis cylinder, does not appear till the fourth month. It is at first
a bipolar prolongation of the nucleus. As it elongates, the nucleus
seems to sit _on_ it, and so loosely that it is easily shifted away by
pressure on the covering glass. Finally the fibre separates entirely
from the nucleus, and _then_ begins to clothe itself with the medullary
sheath. Very curious is the observation that so long as the axis
cylinder is naked it is never varicose, but with the development of the
medulla the primitive axis becomes fluid.
[175] MAYER, _Op. cit._, 393. I cannot, however, agree with MAYER when
he says that the continuity of a nerve-fibre with a cell has _never_
been distinctly shown (p. 395); in the Invertebrata and in the Electric
fishes such a continuity is undeniable; and it has occasionally been
seen in Vertebrata.
[176] RANVIER, in the _Comptes Rendus_, 1875, Vol. LXXXI. p. 1276. This
observation throws light on the fact that cell processes are sometimes
seen entering nerve-roots (§ 124).
The very remarkable observations of Mr. F. BALFOUR, _On the Development
of the Spinal Nerves in Elasmobranch Fishes_ (_Philos. Trans._, Vol.
CLXVI. p. 1), show that the spinal root, ganglion, and nerve-trunk
arise from histological changes in a mass of cells at first all alike;
_not_ that ganglion-cells are formed and from their processes elongate
into fibres. The nerve, he says, forms a continuation of its root
rather than of its ganglion (p. 181); which accords with RANVIER’S view.
[177] In the _Handbuch der menschlichen Anatomie_ of W. KRAUSE, which
has just appeared, I am pleased to find a similar view, p. 376.
[178] On this point consult AXEL KEY and RETZIUS, in the _Archiv für
mikros. Anat._, 1873, p. 308, where the nutritive disturbance is
assigned to the fact that the lymph can no longer take its normal
course. WALLER’S observations on the degeneration of the optic nerves,
with preservation of the integrity of the retina, after division of the
nerves (_Proceedings of Royal Society_, 1856, p. 10), cannot be urged
in support of his view, because BERLIN and LEBERT’S observations are
directly contradictory of his. SAEMISCH _und_ GRAEFE, _Handbuch der
Augenheilkunde_, II. 346. It is said by KRENCHEL that if the nerves
be divided, so as to prevent disturbances in the circulation, no
peripheral degeneration takes place (cited by ENGELMANN in _Pflüger’s
Archiv_, 1875, p. 477).
[179] SCHIFF, _Lehrbuch der Physiologie_, pp. 120, 121.
[180] KÖLLIKER, _Gewebelehre_, 317. SCHWALBE, _Archiv für mikros.
Anat._, 1868, p. 51.
[181] I was first shown this in 1858 by the late Prof. HARLESS in
Munich, who at the same time showed me that the nerve thus bared of
its sheath, if left some hours in gastric juice, split up into regular
discs, like the sarcous elements of muscles.
[182] STIEDA, _Bau des centralen Nervensystem der Amphibien und
Reptilien_, 1875, p. 41.
[183] BUTZKE, in _Archiv für mikroskopische Anatomie_, Bd. III. Heft 3,
p. 596.
[184] Except in the rare cases where there is anastomosis of the
muscle-fibres; as, for example, in the heart. [According to ENGELMANN’S
remarkable researches, the muscles of the heart form a continuum,
so that irritation is propagated from one to the other: _Pflüger’s
Archiv_, 1875, p. 465. This is indubitably the case in the embryonic
heart, as ECKHARD pointed out.] This I hold to be the main cause of
its rhythmic pulsation after removal from the body. Whatever influence
the ganglia may have in exciting this pulsation, such influence would
be powerless were not the muscles so connected; as may be seen in the
other organs which are richly supplied with ganglia, yet do not move
spontaneously; and in organs (such as the ureter or the embryonic
heart, and the hearts of invertebrata) which move spontaneously, yet
have no ganglia.
[185] SCHRÖDER VAN DER KOLK, _Bau und Funktionen der Med. Spinalis_, p.
67.
[186] It is very instructive to learn that for some six months or so
the rat is quite incapable of correctly _localizing_ the pain.
[187] VULPIAN, _Leçons sur le Système Nerveux_, p. 288. The experiment
has been confirmed by ROSENTHAL, and by BIDDER (_Archiv für Anatomie_,
1865, p. 246), who first (in 1842) attempted this union of different
nerves, but arrived at negative results; as did SCHIFF (_Lehrbuch
der Physiol_, 1859, p. 134) and GLUGE _et_ THIERNESSE (_Annales des
Sciences Naturelles_, 1859, p. 181).
[188] SACHS, in the _Archiv für Anat._, 1874, pp. 195, _sq._
[189] LAPLACE, _Essai Philos. sur les Probabilités_, p. 239.
[190] The mode of termination of nerves in muscles is still a point
on which histologists disagree; probably because there is no abrupt
termination, but a blending of the one tissue with the other. In the
Tardigrades, for example, there is actually no appreciable distinction
between nerve and muscle at the point of insertion of the nerve; and
if in the higher animals there is an appreciable difference between
nerve and muscle, there is an inseparable blending of undifferentiated
substance at their point of junction. [According to ENGELMANN’S
recent researches, there seems good reason to suppose that muscles
are composed of contractile substance and a substance which is a
modification of axis-cylinder substance; the first being doubly
refracting, the second isotropic: _Pflüger’s Archiv_, 1875, p. 432.]
[191] SCHIFF, _Lehrbuch_, p. 73.
[192] FREUSBERG observed that the reflex movements in the legs of a
dog whose spine had been divided were considerably lessened after
food or drink. They fell from 95 to 46 pendulum-beats in a minute
after a _litre_ of water had been drunk. See his instructive memoir,
_Reflex-Lähmungen beim Hunde_, in _Pflüger’s Archiv_, 1874, p. 369.
[193] M. HERZEN thus describes the effects of stimulating the vagus
with varying intensities: “Si l’on se sert de l’appareil de Dubois
Raymond, on commence par appliquer une irritation tellement faible
qu’elle ne produit aucun effet; on rapproche alors peu à peu lea
deux bobines de l’appareil avec le plus grand soin, par fractions de
centimètres, par _millimètres_ s’il le faut, et l’on trouve ainsi
le degré d’irritation qui accelère les battements du cœur et qui
produit le maximum de pulsations dans l’unité de temps admise pour
l’expérience. Quand on est là il suffit _d’un millimètre_ de plus pour
faire disparaître l’augmentation, un autre millimètre peut produire une
diminution, et un _troisième_ peut arrêter le cœur complètement. En
reculant alors, en éloignant peu à peu les deux bobines, _on rètourne
à la force qui produit l’augmentation des battements_.” HERZEN,
_Expériences sur les Centres Modérateurs de l’Action Réflexe_, 1864,
p. 68. There have been serious doubts thrown on these experiments; but
several experimenters have confirmed their exactness. Quite recently
they have been confirmed by BULGHERI, _Il Morgagni_, VIII.; and by
ARLOING and TRIPIER, _Archives de Physiologie_, 1872, IV. p. 418. It
must be confessed, however, that the whole subject of the heart’s
innervation is at present very imperfectly understood.
[194] CAYRADE, _Recherches sur les Mouvements Réflexes_, 1864, p. 58.
[195] A frog’s brain is removed, and the body then suspended by the
lower jaw, the legs are allowed to dip into a slightly acidulated
liquid, the chemical action of which stimulates the skin.
[196] I saw a patient in the Berlin _Charité_ whose face and left hand
were in a constant state of convulsive twitching, but no sooner was a
scar on the left hand (where the nerve had been divided) firmly pressed
than the twitchings ceased, and _pain_ was felt; on removal of the
pressure, pain ceased and the twitchings returned.
[197] _Pflüger’s Archiv_, 1875. No one interested in the Reflex Theory
should omit a careful study of the papers by FREUSBERG and GOLTZ. I
have drawn freely from them.
[198] Sir JAMES PAGET has an interesting collection of facts which
illustrate this Law of Arrest, in his paper on “Stammering with other
Organs than those of Speech,” _British Medical Journal_, 1868, Vol. II.
p. 437, reprinted in his _Clinical Lectures and Essays_, 1875, p. 77.
[199] _Archives de Physiol._, 1868, p. 157.
[200] _West Riding Lunatic Asylum Reports_, 1874, p. 200.
[201] CLAUDE BERNARD, _Système Nerveux_, I. 383.
[202] See the excellent remarks of Dr. LAUDER BRUNTON on this point in
his paper on Inhibition in the _West Riding Lunatic Asylum Reports_,
1874, p. 180.
[203] The interesting question of interference has been experimentally
treated by WUNDT in his recently published _Mechanik der Nerven_, 1876,
and theoretically as wave-movement by MEDEM, _Grundzüge einer exakten
Psychologie_, 1876.
[204] On the distinction between first notions and theoretic
conceptions, see _Problems of Life and Mind_, Vol. II. p. 277.
[205] Not transcendental and _a priori_, as Kant teaches; but immanent
in Feeling.
[206] The reader will understand that although mechanical relations
are modes of Feeling, as all other relations are, yet their aspect
is exclusively objective, referring to objects ideally detached from
subjects.
[207] ANTOINE CROS, _Les Fonctions supérieures du Système nerveux_,
1875, p. 85.
[208] The solution offered in the present chapter was first offered
in _Problems of Life and Mind_, 1875, II. 465, _sq._ I mention
this because since the publication of that volume other writers
have expressed the same ideas, sometimes using my language and
illustrations: e. g. M. TAINE in the _Revue Philosophique_, January,
1877, art., _Les Vibrations cérébrales et la Pensée_.
[209] _Problems of Life and Mind_, Vol. II. pp. 443 and 482.
[210] “The retinal image is the last effect known of the action
of objects on us; what happens beyond the retina we know not;
our knowledge of the objective process has at present here its
limit.”--EWALD HERING, _Beiträge zur Physiologie_, 1862, p. 166. That
is to say, we have a definite translation of the process in geometric
terms as far as the retina, and thence onwards Geometry fails us, and
Neurology and Psychology are invoked.
[211] Compare PROBLEM II. Chap. IV.
[212] “Das Bewusstwerden ist nichts Anderes als ein weiter
fortgeschrittenes Erinnern oder Neuwerden des von aussen aufgenommenen
Wissens, ein innerliches Wissen dieses Wissens oder ein in sich
reflectirtes Wissen.”--JESSEN, _Versuch einer Wissenschaftlichen
Begründung der Psychologie_, 1855, p. 477.
[213] In common language a stone or a tree is said to be unconscious;
but this is an anthropomorphic extension of the term. In strictness we
should no more speak of unconsciousness outside the sphere of Sentience
than of darkness outside the sphere of Vision.
[214] The contraction may be effected in the eye out of the organism.
See p. 229. It is then no reflex.
[215] _Glasgow Medical Journal_, 1857, p. 451. See also further on,
note to p. 426.
[216] MAYER, _Die Elementarorganisation des Seelenorgans_, p. 12, is
the authority for the last statement.
[217] _Allgemeine Zeitschrift für Psychiatrie_, Bd. 31, p. 711.
[218] AUBERT, _Grundrüge der physiol. Optik_, 1876, p. 633. “The
accommodative movement of the eye is to be considered voluntary. It is
true we contract the pupil without being conscious of the contraction
of muscular fibres, _but this holds good for every voluntary movement_.
When a person raises the tone of his voice he is not conscious that
by muscular contraction he makes his chordæ vocales more tense; he
attains his object without being aware of the means by which he does
so. The same is applicable to accommodation for near objects and to
the contraction of the pupil accompanying it. The fact that _this last
is only an associated movement does not deprive it of its voluntary
character_, for there is perhaps no single muscle which can contract
entirely by itself.” DONDERS, _On the Anomalies of Accommodation_,
1864, p. 574. Professor BEER of Bonn has the rare power of contracting
or dilating the pupils of his eye at will; here ideas act as motors.
When he thinks of a very dark space the pupil dilates, when of a very
bright spot the pupil contracts. (NOBLE, _The Human Mind_, 1858, p.
124.) I believe this to be only an exaggerated form of the normal
tendency. In all of us the mechanism is so disposed that the feelings
of dilatation are associated with feelings (and consequently ideas) of
darkness; and by this association a reversal of the process obtains, so
that the idea of darkness calls up the feeling it symbolizes.
[219] SPENCER, _Principles of Psychology_, I. 499.
[220] DESCARTES expressly calls them sensitive machines. He refuses
them Thought, but neither “la vie ou le sentiment.” He adds, “Mon
opinion n’est pas que les bêtes voient comme nous lorsque nous sentons
que nous voyons.”--_Œuvres_, IV. p. 339. This example is cited by him
in proof of human automatism: “Que ce n’est point par l’entremise de
notre âme que les yeux se ferment, puisque c’est contre notre volonté,
laquelle est sa seule ou du moins sa principale action; mais c’est
à cause que la machine de notre corps est tellement composée que le
mouvement de cette main vers nos yeux excite un autre mouvement en
notre cerveau qui conduit les esprits animaux dans les muscles qui font
abaisser les paupières.” All indeed that we assign to Sensibility, he
assigns to these hypothetical animal spirits, and thence he concludes,
“Qu’il ne reste rien en nous que nous devions attribuer à notre âme
sinon nos pensées.”--_Les Passions de l’Âme_, art. 13 and 17. Comp.
_Discours de la Méthode_, partie iv.
[221] DESCARTES compares the animal mechanism to that of the grottos
and fountains at Versailles, the nerves to the water-tubes:--“Les
objets extérieurs qui par leur seul présence, agissent contre les
organes des sens, et qui par ce moyen, la déterminent à se mouvoir
en plusieurs diverses façons, selon comme les parties du cerveau
sont disposées, sont comme les étrangers, qui entrant dans quelques
unes des grottes de ces fontaines causent euxmêmes sans y penser les
mouvements qui s’y font en leur présence: car ils n’y peuvent entrer
qu’en marchant sur certains carreaux tellement disposés, que s’ils
approchent d’une Diane qui se baigne, ils la font cacher dans les
roseaux; et s’ils passent outre pour la poursuivre, ils feront venir
vers eux un Neptune qui les menacera de son trident; ou s’ils vont de
quelque autre costé, ils en feront sortir un monstre marin qui leur
vomira de l’eau contre la face.”--_Traité de l’Homme_, 1664, p. 12.
Ingenious as the comparison is, it only illustrates how machines may
be constructed to imitate animal actions. Diana always hides herself
when a certain spot is trodden upon; and Neptune always appears when
another spot is trodden upon. There is no fluctuation, no sensibility
discerning differences and determining variations. Compare the
following experiment: A monkey was placed on the table and a shrill
whistle made close to its ear: “Immediately the ear was pricked and
the animal turned with an air of intense surprise, with eyes widely
opened and pupils dilated, to the direction whence the sound proceeded.
On repetition of the experiment several times, though the pricking
of the ear and the turning of the head and eyes constantly occurred,
the look of surprise and dilatation of the pupils ceased to be
manifested.”--FERRIER, _The Functions of the Brain_, 1876, p. 171. A
mechanical monkey would always have reacted in precisely the same way
on each stimulus.
[222] Printed in the _Fortnightly Review_, November, 1874, from which
all my citations are made.
[223] SCHIFF, _Lehrbuch der Physiol._, 1858, p. 212. HERMANN,
_Physiology_, translated by GAMGEE, 1875, p. 511.
[224] Meanwhile the reader is referred to SCHRÖDER VAN DER KOLK,
_Pathologie der Geisteskrankheiten_, 1863, p. 51; or JESSEN,
_Physiologie des menschlichen Denkens_, 1872, p. 66.
[225] GRIESINGER, _Les Maladies Mentales_, p. 96.
[226] M. LUYS cites the case of a patient who conversed quite
rationally with a visitor “sans en avoir conscience, et ne se
souvenait de rien”; and he draws the extraordinary conclusion that
the conversation “s’opérait en vertu des forces réflexes.”--_Études
de Physiologie et de Pathologie Cérébrales_, 1874, p. 117. Is it
not obvious that the patient must have been conscious at the time,
though the consciousness vanished like that in a dream? The persistent
consciousness is the continuous linking on of one state with previous
states--the apperception of the past.
[227] ABERCROMBIE, _Inquiries concerning the Intellectual Powers_,
1840, p. 151. WIGAN, _The Duality of the Mind_, 1844, p. 270. DESPINE,
_La Psychologie Naturelle_, 1868, I. 54.
[228] Dr. HUGHLINGS JACKSON has quite recently cited some curious
examples in his own practice. See _West Riding Lunatic Asylum Reports
for 1875_.
[229] PROBLEMS, Vol. II. p. 478, _sq._
[230] “Le sentiment fait naître le mouvement, et le mouvement donne
naissance au sentiment.”--VAN DEEN, _Traités et Découvertes sur la
Moëlle Épinière_, 1841, p. 102.
[231] Dr. CARPENTER tells a similar story of Admiral CODRINGTON, who,
when a midshipman, could always be awakened from the profoundest
slumber if the word “signal” were uttered; whereas no other word
disturbed him.
[232] Compare an interesting personal example given by JOUFFROY, quoted
in Sir W. HAMILTON’S _Lectures_, I. 331.
[233] _Lancet_, 10th July, 1858.
[234] MARSHALL HALL in _Philos. Trans._, 1833. _Lectures on the Nervous
System and its Diseases_, 1836. _New Memoir on the Nervous System_,
1843.
[235] MÜLLER, _Physiology_, I. 721.
[236] It is better simply to remove the brain, than to remove the whole
head, which causes a serious loss of blood. An etherized animal may be
operated on with ease and accuracy. For many experiments, mere division
of the spinal cord is better than decapitation. Great variations in the
results must be expected, because the condition of the animal, its age
and sex--whether fasting or digesting--whether the season be spring or
summer--and a hundred other causes, complicate the experiment.
[237] VOLKMANN, quoted by PFLÜGER.
[238] UNZER, _The Principles of Physiology_ (translated for the
Sydenham Society), p. 235.
[239] Even so eminent an investigator as GOLTZ has fallen into this
confusion. He introduces an experiment to prove that the brainless
frog is insensible to pain by the words “when an animal, placed under
circumstances which would be very painful, makes no movement, although
quite capable of moving, the least we can say is that it is improbable
that the animal has sensation” (_Nervencentren des Frosches_, p.
127). I need not discuss the proof itself, having already done so in
_Nature_, Vol. IX. p. 84. The point to which I wish to call attention
is the confusion of insensibility in general with insensibility to pain.
[240] See DUCHENNE, _De Électrisation localisée_, p. 398. GRIESINGER
cites various examples of insane patients who have burned the flesh off
their bones while manifesting a total indifference to these injuries.
_Maladies Mentales_, p. 94. FALRET says, “Nous avons vu plusieurs
fois des aliénés s’inciser, s’amputer eux-mêmes diverses parties du
corps sans paraître ressentir aucune souffrance.” _Leçons cliniques
de Médicine Mentale_, 1854, I. 189. Patients incapable of feeling the
contact of a hot iron with their skin have felt subjective burnings in
the skin thus objectively insensible.
[241] CROS, _Les Fonctions supérieures du Syst. nerveux_, 1875, p. 27.
[242] _Virchow’s Archiv_, Bd. XXVIII. p. 30.
[243] The idea of a _fixed anatomical mechanism_ for reflexion, such
as that of an excito-motory system, is completely refuted by the fact
that the gray substance may anywhere be cut sway, and yet so long
as a small bridge of gray substance remains the stimulation will be
propagated through it. The idea of a _fixed pathway_ is also refuted by
the fact of the variations in the reflex responses, and the necessary
irradiation even for very simple reflexes. Take, for example, that of
breathing. An irritation of the bronchial filaments is transmitted by
the pneumogastric to its centre in the medulla oblongata; from this,
however, it is immediately irradiated _downwards_ to the cervical and
dorsal regions, which innervate the muscles of chest and diaphragm, and
_upwards_ to the brain, whether the stimulation awaken consciousness or
not. One may say, indeed, that inasmuch as under normal conditions the
bronchial irritation always causes a movement of a particular group of
muscles, there is to this extent a fixed pathway of discharge; but, as
I have formerly explained, this is only an expression of the particular
tension of particular centres, and is variable with that tension; the
other centres are also affected, even when they are not excited to
discharge.
[244] LALLEMAND, _Recherches sur L’Encéphale_, III. 310.
[245] _West Riding Lunatic Asylum Reports_, 1875, Vol. V. pp. 252, _sq._
[246] GALL _et_ SPURZHEIM, _Anat. et Physiol. du Système Nerveux_, I.
83.
[247] Printed in the _British and Foreign Medical Review_, Jan. 1845.
[248] GRIESINGER, _Abhandlungen_, 1872. The first volume contains a
reprint of this memoir.
[249] LANDRY, _Traité des Paralysies_, I. 55. Conf. ZIEMSSEN, _Chorea_
in the _Handbuch der speciellen Pathologie_, Bd. XII. 2, p. 408. And
LUYS, _Études de physiol. et pathol. cérébrales_, 1874, pp. 89–94.
[250] SUE, _Recherches Philosophiques sur la Vitalité et le
Galvanisme_, p. 9. He was not consistent, however, but adopted Bichat’s
opinion respecting the sensibility of the viscera, p. 68.
[251] LEGALLOIS, _Expériences sur le principe de la vie_. Published,
I conclude, in 1811; the edition I use is the one printed in the
_Encyclopédie des Sciences Medicales_, IV.
[252] WILSON PHILIP, _Experimental Inquiry into the Laws of the Vital
Functions_, pp. 209, 210.
[253] LONGET, _Traité de Physiologie_, II. 105.
[254] He cites Cuvier, Majendie, Deamoulins, and Mayo as maintaining
this error.
[255] GRAINGER, _Structure and Functions of the Spinal Cord_, p. 66.
[256] NASSE, _Unters. zur Physiologie und Pathologie_, Vol. II. Part 2.
[257] CARUS, _System der Physiologie_, III. 101.
[258] J. W. ARNOLD, _Die Lehre von der Reflex-Function_, 86.
[259] PFLÜGER, _Die sensorischen Functionen des Rückenmarks der
Wirbelthiere_.
[260] Except AUERBACH, who repeated and varied the experiments; and
FUNKE, who partially adopted the conclusions in his systematic treatise
on Physiology.
[261] SCHIFF, _Lehrbuch der Physiologie_, 208.
[262] LANDRY, _Traité des Paralysies_, 1859, maintains that the cord is
a centre of sensation, and that there is in it a faculty _analogous_
to the perception and judgment of the brain. Compare pp. 163 _et sq._
and 305. He also cites an essay by Dr. PATON of Edinburgh (_Edinburgh
Medical Journal_, 1846), in which the sensational and volitional claims
of the spinal cord are advanced.
[263] GOLTZ, _Beiträge zur Lehre von den Functionen der Nervencentren
des Froeches_, 1869.
[264] _Pflüger’s Archiv_, Bd. XIV. p. 158.
[265] See Prob. II. § 183.
[266] “Il y a donc une mémoire par le cerveau et une mémoire par
l’automate. Tous les organes ont une mémoire propre, c’est à dire _une
tendance à_ reproduire les séries d’actes qu’ils ont plusieurs fois
executés.”--GRATIOLET, _Anat. du Système Nerveux_, 1857, p. 464.
[267] To obviate misunderstanding let me say that, unless the contrary
is specified, I use the term Brain throughout this argument as
equivalent to the cerebral hemispheres, because it is in these that
sensation, volition, and consciousness are localized by the generality
of writers, many of whom, indeed, regard the cells of the gray matter
of the convolutions as the exclusive seat of these phenomena, dividing
these cells into sensational, emotional, and intellectual. There
are physiologists who extend sensation to the cerebral ganglia and
gray masses of the medulla oblongata; but the medulla spinalis is so
clearly continuous with the medulla oblongata that there is a glaring
inconsistency in excluding sensation from the one if it is accorded to
the other; and the grounds on which sensitive phenomena are admitted in
the absence of the hemispheres, force us to admit analogous phenomena
in the absence of the ganglia and medulla oblongata: in each case the
phenomena are less complex and varied as the mechanisms become less
complex.
[268] Compare LUSSANA e LEMOIGNE, _Fisiologia dei centri encefalici_,
1871, II. 239, 240, 330.
[269] See a very interesting case of this special loss of memory
in a priest who still occupied himself reading classic authors and
performing his official duties many months after an injury to the
brain. LUSSANA e LEMOIGNE, _Fisiologia dei centri encefalici_, I. 201.
[270] BOUILLAUD, _Recherches Expérimentales sur les Fonctions du
Cerveau en général_, 1830, p. 5, _sq._
[271] LONGET, _Traité de Physiologie_, II. 240.
[272] DALTON, _Human Physiology_, Philadelphia, 1859, p. 362.
[273] DALTON, p. 362.
[274] DALTON, p. 363.
[275] FLOURENS, p. 89.
[276] LEYDEN in the _Berliner klinische Wochenschrift_, 1867, No. 7.
MEISSNER, _Jahresbericht über Physiol._, 1867, p. 410.
[277] VOIT in the _Sitzungsberichte der Münchener Academie_, 1868, p.
105. Comp. also GOLTZ in _Pflüger’s Archiv_, Bd. XIV. 435.
[278] VULPIAN, _Système Nerveux_, 542–48.
[279] For other examples see GINTRAC, _Pathologie Interne_, 1868, VI.
51–57.
[280] If the water is perfectly still the fish sinks to the bottom and
remains motionless until the water be stirred. Mere _contact_ does not
suffice; there must be intermittent pulses from the moving water.
[281] LUSSANA e LEMOIGNE, _Op. cit._, I. 15.
[282] _Archives de Physiologie_, 1869, p. 539.
[283] BRÜCKE, _Physiologie_, II. p. 53. While these sheets are passing
through the press, GOLTZ has published his second series of experiments
on the brain. The following detail is a good illustration of what is
said in the text: A dog deprived of a portion of both hemispheres
displayed a marked imperfection in the execution of ordinary instincts.
Although sight was impaired he could see, and recognize men and certain
objects: the sight of a whip made him cower, but the sight of meat
did not suffice to set the feeding mechanism in action. When meat
was suspended above his head, the scent caused him to sniff about in
search, but he failed to find it, and even when he was so placed that
he could see the suspended meat, the _unusual_ impression failed to
guide him. If the meat were held towards him, or placed before him in
a dish, he took it at once--this being the customary stimulation. So
also, if the hand were held up, in the usual way when dogs are made
to leap for food, this dog sprang vigorously up and caught the food;
but he would spring up in the same way when the hand was held empty,
and continue fruitlessly springing, whereas an uninjured dog ceases to
spring when he sees the hand is empty.--_Pflüger’s Archiv_, Bd. XIV. p.
419.
[284] GRATIOLET, _Anat. Comparée du Système Nerveux_, 1857, p. 459.
[285] LUSSANA e LEMOIGNE, _Op. cit._, I. 363.
[286] _Virchow’s Archiv_, Bd. LX. pp. 130–33. Yet there are many
physiologists who persist in placing the _motorium commune_ in the
_corpora strata_! And they place the _sensorium commune_ in the optic
thalami, although, not to mention the ambiguous evidence of Pathology,
the experiments of NOTHENGEL and VEYSSIÈRE show that destruction of
the thalami does not destroy sensation. See VEYSSIÈRE, _Recherches
sur l’hémianesthésie de cause cérébrale_, 1874, pp. 83, 84. I may
observe, in passing, that the notion of the _corpora striata_ being
the necessary channel for volitional impulses, and the _optic thalami_
for reflex actions, is utterly disproved by the experimental evidence
recorded in the text, as well as in § 66.
[287] _Pflüger’s Archiv_, Bde. VIII. and IX.
Transcriber’s Notes
Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in the original book; otherwise they
were not changed.
Simple typographical errors were corrected; unbalanced quotation
marks were remedied when the change was obvious, and otherwise left
unbalanced.
Illustrations in this eBook have been positioned between paragraphs and
nearer to the text that references them.
Footnotes in this eBook have been collected and moved to the end of the
book.
The Table of Contents entry for Problem II, Chapter II, referenced the
wrong page; corrected here.
*** End of this LibraryBlog Digital Book "Problems of Life and Mind. Second series: The Physical Basis of Mind" ***
Copyright 2023 LibraryBlog. All rights reserved.