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Title: A History of Science — Volume 4
Author: Williams, Henry Smith, 1863-1943, Williams, Edward Huntington, 1868-1944
Language: English
As this book started as an ASCII text book there are no pictures available.

*** Start of this LibraryBlog Digital Book "A History of Science — Volume 4" ***


By Henry Smith Williams, M.D., LL.D.

Assisted By Edward H. Williams, M.D.

In Five Volumes

Volume IV.



AS regards chronology, the epoch covered in the present volume is
identical with that viewed in the preceding one. But now as regards
subject matter we pass on to those diverse phases of the physical world
which are the field of the chemist, and to those yet more intricate
processes which have to do with living organisms. So radical are the
changes here that we seem to be entering new worlds; and yet, here as
before, there are intimations of the new discoveries away back in the
Greek days. The solution of the problem of respiration will remind
us that Anaxagoras half guessed the secret; and in those diversified
studies which tell us of the Daltonian atom in its wonderful
transmutations, we shall be reminded again of the Clazomenian
philosopher and his successor Democritus.

Yet we should press the analogy much too far were we to intimate that
the Greek of the elder day or any thinker of a more recent period had
penetrated, even in the vaguest way, all of the mysteries that the
nineteenth century has revealed in the fields of chemistry and biology.
At the very most the insight of those great Greeks and of the wonderful
seventeenth-century philosophers who so often seemed on the verge of our
later discoveries did no more than vaguely anticipate their successors
of this later century. To gain an accurate, really specific knowledge of
the properties of elementary bodies was reserved for the chemists of a
recent epoch. The vague Greek questionings as to organic evolution were
world-wide from the precise inductions of a Darwin. If the mediaeval
Arabian endeavored to dull the knife of the surgeon with the use of
drugs, his results hardly merit to be termed even an anticipation
of modern anaesthesia. And when we speak of preventive medicine--of
bacteriology in all its phases--we have to do with a marvellous field of
which no previous generation of men had even the slightest inkling.

All in all, then, those that lie before us are perhaps the most
wonderful and the most fascinating of all the fields of science. As
the chapters of the preceding book carried us out into a macrocosm of
inconceivable magnitude, our present studies are to reveal a microcosm
of equally inconceivable smallness. As the studies of the physicist
attempted to reveal the very nature of matter and of energy, we have now
to seek the solution of the yet more inscrutable problems of life and of


The development of the science of chemistry from the "science" of
alchemy is a striking example of the complete revolution in the attitude
of observers in the field of science. As has been pointed out in a
preceding chapter, the alchemist, having a preconceived idea of how
things should be, made all his experiments to prove his preconceived
theory; while the chemist reverses this attitude of mind and bases his
conceptions on the results of his laboratory experiments. In short,
chemistry is what alchemy never could be, an inductive science. But
this transition from one point of view to an exactly opposite one was
necessarily a very slow process. Ideas that have held undisputed sway
over the minds of succeeding generations for hundreds of years cannot
be overthrown in a moment, unless the agent of such an overthrow be so
obvious that it cannot be challenged. The rudimentary chemistry that
overthrew alchemy had nothing so obvious and palpable.

The great first step was the substitution of the one principle,
phlogiston, for the three principles, salt, sulphur, and mercury. We
have seen how the experiment of burning or calcining such a metal
as lead "destroyed" the lead as such, leaving an entirely different
substance in its place, and how the original metal could be restored by
the addition of wheat to the calcined product. To the alchemist this was
"mortification" and "revivification" of the metal. For, as pointed
out by Paracelsus, "anything that could be killed by man could also be
revivified by him, although this was not possible to the things killed
by God." The burning of such substances as wood, wax, oil, etc., was
also looked upon as the same "killing" process, and the fact that the
alchemist was unable to revivify them was regarded as simply the lack of
skill on his part, and in no wise affecting the theory itself.

But the iconoclastic spirit, if not the acceptance of all the teachings,
of the great Paracelsus had been gradually taking root among the better
class of alchemists, and about the middle of the seventeenth century
Robert Boyle (1626-1691) called attention to the possibility of making
a wrong deduction from the phenomenon of the calcination of the metals,
because of a very important factor, the action of the air, which was
generally overlooked. And he urged his colleagues of the laboratories to
give greater heed to certain other phenomena that might pass unnoticed
in the ordinary calcinating process. In his work, The Sceptical Chemist,
he showed the reasons for doubting the threefold constitution of matter;
and in his General History of the Air advanced some novel and carefully
studied theories as to the composition of the atmosphere. This was an
important step, and although Boyle is not directly responsible for the
phlogiston theory, it is probable that his experiments on the atmosphere
influenced considerably the real founders, Becker and Stahl.

Boyle gave very definitely his idea of how he thought air might be
composed. "I conjecture that the atmospherical air consists of three
different kinds of corpuscles," he says; "the first, those numberless
particles which, in the form of vapors or dry exhalations, ascend
from the earth, water, minerals, vegetables, animals, etc.; in a word,
whatever substances are elevated by the celestial or subterraneal heat,
and thence diffused into the atmosphere. The second may be yet more
subtle, and consist of those exceedingly minute atoms, the magnetical
effluvia of the earth, with other innumerable particles sent out from
the bodies of the celestial luminaries, and causing, by their influence,
the idea of light in us. The third sort is its characteristic and
essential property, I mean permanently elastic parts. Various hypotheses
may be framed relating to the structure of these later particles of the
air. They might be resembled to the springs of watches, coiled up and
endeavoring to restore themselves; to wool, which, being compressed,
has an elastic force; to slender wires of different substances,
consistencies, lengths, and thickness; in greater curls or less,
near to, or remote from each other, etc., yet all continuing springy,
expansible, and compressible. Lastly, they may also be compared to the
thin shavings of different kinds of wood, various in their lengths,
breadth, and thickness. And this, perhaps, will seem the most eligible
hypothesis, because it, in some measure, illustrates the production
of the elastic particles we are considering. For no art or curious
instruments are required to make these shavings whose curls are in no
wise uniform, but seemingly casual; and what is more remarkable, bodies
that before seemed unelastic, as beams and blocks, will afford them."(1)

Although this explanation of the composition of the air is most crude,
it had the effect of directing attention to the fact that the
atmosphere is not "mere nothingness," but a "something" with a
definite composition, and this served as a good foundation for future
investigations. To be sure, Boyle was neither the first nor the only
chemist who had suspected that the air was a mixture of gases, and not
a simple one, and that only certain of these gases take part in the
process of calcination. Jean Rey, a French physician, and John Mayow, an
Englishman, had preformed experiments which showed conclusively that the
air was not a simple substance; but Boyle's work was better known, and
in its effect probably more important. But with all Boyle's explanations
of the composition of air, he still believed that there was an
inexplicable something, a "vital substance," which he was unable to
fathom, and which later became the basis of Stahl's phlogiston theory.
Commenting on this mysterious substance, Boyle says: "The difficulty
we find in keeping flame and fire alive, though but for a little time,
without air, renders it suspicious that there be dispersed through the
rest of the atmosphere some odd substance, either of a solar, astral, or
other foreign nature; on account of which the air is so necessary to the
substance of flame!" It was this idea that attracted the attention
of George Ernst Stahl (1660-1734), a professor of medicine in the
University of Halle, who later founded his new theory upon it. Stahl's
theory was a development of an earlier chemist, Johann Joachim Becker
(1635-1682), in whose footsteps he followed and whose experiments he
carried further.

In many experiments Stahl had been struck with the fact that certain
substances, while differing widely, from one another in many respects,
were alike in combustibility. From this he argued that all combustible
substances must contain a common principle, and this principle he named
phlogiston. This phlogiston he believed to be intimately associated in
combination with other substances in nature, and in that condition not
perceivable by the senses; but it was supposed to escape as a substance
burned, and become apparent to the senses as fire or flame. In other
words, phlogiston was something imprisoned in a combustible structure
(itself forming part of the structure), and only liberated when this
structure was destroyed. Fire, or flame, was FREE phlogiston, while the
imprisoned phlogiston was called COMBINED PHLOGISTON, or combined fire.
The peculiar quality of this strange substance was that it disliked
freedom and was always striving to conceal itself in some combustible
substance. Boyle's tentative suggestion that heat was simply motion was
apparently not accepted by Stahl, or perhaps it was unknown to him.

According to the phlogistic theory, the part remaining after a substance
was burned was simply the original substance deprived of phlogiston. To
restore the original combustible substance, it was necessary to heat the
residue of the combustion with something that burned easily, so that the
freed phlogiston might again combine with the ashes. This was explained
by the supposition that the more combustible a substance was the more
phlogiston it contained, and since free phlogiston sought always to
combine with some suitable substance, it was only necessary to mix the
phlogisticating agents, such as charcoal, phosphorus, oils, fats, etc.,
with the ashes of the original substance, and heat the mixture, the
phlogiston thus freed uniting at once with the ashes. This theory fitted
very nicely as applied to the calcined lead revivified by the grains of
wheat, although with some other products of calcination it did not seem
to apply at all.

It will be seen from this that the phlogistic theory was a step towards
chemistry and away from alchemy. It led away from the idea of a "spirit"
in metals that could not be seen, felt, or appreciated by any of the
senses, and substituted for it a principle which, although a falsely
conceived one, was still much more tangible than the "spirit," since it
could be seen and felt as free phlogiston and weighed and measured as
combined phlogiston. The definiteness of the statement that a metal,
for example, was composed of phlogiston and an element was much less
enigmatic, even if wrong, than the statement of the alchemist that
"metals are produced by the spiritual action of the three principles,
salt, mercury, sulphur"--particularly when it is explained that salt,
mercury, and sulphur were really not what their names implied, and that
there was no universally accepted belief as to what they really were.

The metals, which are now regarded as elementary bodies, were considered
compounds by the phlogistians, and they believed that the calcining of
a metal was a process of simplification. They noted, however, that the
remains of calcination weighed more than the original product, and the
natural inference from this would be that the metal must have taken in
some substance rather than have given off anything. But the phlogistians
had not learned the all-important significance of weights, and their
explanation of variation in weight was either that such gain or loss
was an unimportant "accident" at best, or that phlogiston, being light,
tended to lighten any substance containing it, so that driving it out of
the metal by calcination naturally left the residue heavier.

At first the phlogiston theory seemed to explain in an indisputable way
all the known chemical phenomena. Gradually, however, as experiments
multiplied, it became evident that the plain theory as stated by Stahl
and his followers failed to explain satisfactorily certain laboratory
reactions. To meet these new conditions, certain modifications were
introduced from time to time, giving the theory a flexibility that
would allow it to cover all cases. But as the number of inexplicable
experiments continued to increase, and new modifications to the theory
became necessary, it was found that some of these modifications were
directly contradictory to others, and thus the simple theory became
too cumbersome from the number of its modifications. Its supporters
disagreed among themselves, first as to the explanation of certain
phenomena that did not seem to accord with the phlogistic theory, and
a little later as to the theory itself. But as yet there was no
satisfactory substitute for this theory, which, even if unsatisfactory,
seemed better than anything that had gone before or could be suggested.

But the good effects of the era of experimental research, to which the
theory of Stahl had given such an impetus, were showing in the attitude
of the experimenters. The works of some of the older writers, such
as Boyle and Hooke, were again sought out in their dusty corners and
consulted, and their surmises as to the possible mixture of various
gases in the air were more carefully considered. Still the phlogiston
theory was firmly grounded in the minds of the philosophers, who can
hardly be censured for adhering to it, at least until some satisfactory
substitute was offered. The foundation for such a theory was finally
laid, as we shall see presently, by the work of Black, Priestley,
Cavendish, and Lavoisier, in the eighteenth century, but the phlogiston
theory cannot be said to have finally succumbed until the opening years
of the nineteenth century.



Modern chemistry may be said to have its beginning with the work of
Stephen Hales (1677-1761), who early in the eighteenth century began his
important study of the elasticity of air. Departing from the point of
view of most of the scientists of the time, he considered air to be "a
fine elastic fluid, with particles of very different nature floating in
it"; and he showed that these "particles" could be separated. He pointed
out, also, that various gases, or "airs," as he called them, were
contained in many solid substances. The importance of his work, however,
lies in the fact that his general studies were along lines leading away
from the accepted doctrines of the time, and that they gave the impetus
to the investigation of the properties of gases by such chemists as
Black, Priestley, Cavendish, and Lavoisier, whose specific discoveries
are the foundation-stones of modern chemistry.


The careful studies of Hales were continued by his younger confrere, Dr.
Joseph Black (1728-1799), whose experiments in the weights of gases and
other chemicals were first steps in quantitative chemistry. But even
more important than his discoveries of chemical properties in general
was his discovery of the properties of carbonic-acid gas.

Black had been educated for the medical profession in the University of
Glasgow, being a friend and pupil of the famous Dr. William Cullen. But
his liking was for the chemical laboratory rather than for the practice
of medicine. Within three years after completing his medical course,
and when only twenty-three years of age, he made the discovery of the
properties of carbonic acid, which he called by the name of "fixed air."
After discovering this gas, Black made a long series of experiments,
by which he was able to show how widely it was distributed throughout
nature. Thus, in 1757, he discovered that the bubbles given off in
the process of brewing, where there was vegetable fermentation, were
composed of it. To prove this, he collected the contents of these
bubbles in a bottle containing lime-water. When this bottle was
shaken violently, so that the lime-water and the carbonic acid became
thoroughly mixed, an insoluble white powder was precipitated from the
solution, the carbonic acid having combined chemically with the lime
to form the insoluble calcium carbonate, or chalk. This experiment
suggested another. Fixing a piece of burning charcoal in the end of a
bellows, he arranged a tube so that the gas coming from the charcoal
would pass through the lime-water, and, as in the case of the bubbles
from the brewer's vat, he found that the white precipitate was thrown
down; in short, that carbonic acid was given off in combustion. Shortly
after, Black discovered that by blowing through a glass tube inserted
into lime-water, chalk was precipitated, thus proving that carbonic acid
was being constantly thrown off in respiration.

The effect of Black's discoveries was revolutionary, and the attitude
of mind of the chemists towards gases, or "airs," was changed from that
time forward. Most of the chemists, however, attempted to harmonize the
new facts with the older theories--to explain all the phenomena on the
basis of the phlogiston theory, which was still dominant. But while many
of Black's discoveries could not be made to harmonize with that
theory, they did not directly overthrow it. It required the additional
discoveries of some of Black's fellow-scientists to complete its
downfall, as we shall see.


This work of Black's was followed by the equally important work of
his former pupil, Henry Cavendish (1731-1810), whose discovery of the
composition of many substances, notably of nitric acid and of water,
was of great importance, adding another link to the important chain of
evidence against the phlogiston theory. Cavendish is one of the most
eccentric figures in the history of science, being widely known in his
own time for his immense wealth and brilliant intellect, and also for
his peculiarities and his morbid sensibility, which made him dread
society, and probably did much in determining his career. Fortunately
for him, and incidentally for the cause of science, he was able to
pursue laboratory investigations without being obliged to mingle with
his dreaded fellow-mortals, his every want being provided for by the
immense fortune inherited from his father and an uncle.

When a young man, as a pupil of Dr. Black, he had become imbued with the
enthusiasm of his teacher, continuing Black's investigations as to the
properties of carbonic-acid gas when free and in combination. One of his
first investigations was reported in 1766, when he communicated to
the Royal Society his experiments for ascertaining the properties of
carbonic-acid and hydrogen gas, in which he first showed the possibility
of weighing permanently elastic fluids, although Torricelli had before
this shown the relative weights of a column of air and a column of
mercury. Other important experiments were continued by Cavendish, and
in 1784 he announced his discovery of the composition of water, thus
robbing it of its time-honored position as an "element." But his
claim to priority in this discovery was at once disputed by his
fellow-countryman James Watt and by the Frenchman Lavoisier. Lavoisier's
claim was soon disallowed even by his own countrymen, but for many
years a bitter controversy was carried on by the partisans of Watt and
Cavendish. The two principals, however, seem never to have entered
into this controversy with anything like the same ardor as some of their
successors, as they remained on the best of terms.(1) It is certain, at
any rate, that Cavendish announced his discovery officially before Watt
claimed that the announcement had been previously made by him, "and,
whether right or wrong, the honor of scientific discoveries seems to be
accorded naturally to the man who first publishes a demonstration of his
discovery." Englishmen very generally admit the justness of Cavendish's
claim, although the French scientist Arago, after reviewing the evidence
carefully in 1833, decided in favor of Watt.

It appears that something like a year before Cavendish made known his
complete demonstration of the composition of water, Watt communicated
to the Royal Society a suggestion that water was composed of
"dephlogisticated air (oxygen) and phlogiston (hydrogen) deprived of
part of its latent heat." Cavendish knew of the suggestion, but in his
experiments refuted the idea that the hydrogen lost any of its latent
heat. Furthermore, Watt merely suggested the possible composition
without proving it, although his idea was practically correct, if we can
rightly interpret the vagaries of the nomenclature then in use. But
had Watt taken the steps to demonstrate his theory, the great "Water
Controversy" would have been avoided. Cavendish's report of his
discovery to the Royal Society covers something like forty pages of
printed matter. In this he shows how, by passing an electric spark
through a closed jar containing a mixture of hydrogen gas and oxygen,
water is invariably formed, apparently by the union of the two gases.
The experiment was first tried with hydrogen and common air, the oxygen
of the air uniting with the hydrogen to form water, leaving the nitrogen
of the air still to be accounted for. With pure oxygen and hydrogen,
however, Cavendish found that pure water was formed, leaving slight
traces of any other, substance which might not be interpreted as being
Chemical impurities. There was only one possible explanation of this
phenomenon--that hydrogen and oxygen, when combined, form water.

"By experiments with the globe it appeared," wrote Cavendish, "that when
inflammable and common air are exploded in a proper proportion, almost
all the inflammable air, and near one-fifth the common air, lose their
elasticity and are condensed into dew. And by this experiment it appears
that this dew is plain water, and consequently that almost all the
inflammable air is turned into pure water.

"In order to examine the nature of the matter condensed on firing a
mixture of dephlogisticated and inflammable air, I took a glass
globe, holding 8800 grain measures, furnished with a brass cock and an
apparatus for firing by electricity. This globe was well exhausted by
an air-pump, and then filled with a mixture of inflammable and
dephlogisticated air by shutting the cock, fastening the bent glass tube
into its mouth, and letting up the end of it into a glass jar inverted
into water and containing a mixture of 19,500 grain measures of
dephlogisticated air, and 37,000 of inflammable air; so that, upon
opening the cock, some of this mixed air rushed through the bent tube
and filled the globe. The cock was then shut and the included air fired
by electricity, by means of which almost all of it lost its elasticity
(was condensed into water vapors). The cock was then again opened so as
to let in more of the same air to supply the place of that destroyed by
the explosion, which was again fired, and the operation continued till
almost the whole of the mixture was let into the globe and exploded.
By this means, though the globe held not more than a sixth part of the
mixture, almost the whole of it was exploded therein without any fresh
exhaustion of the globe."

At first this condensed matter was "acid to the taste and contained
two grains of nitre," but Cavendish, suspecting that this was due to
impurities, tried another experiment that proved conclusively that his
opinions were correct. "I therefore made another experiment," he says,
"with some more of the same air from plants in which the proportion of
inflammable air was greater, so that the burnt air was almost completely
phlogisticated, its standard being one-tenth. The condensed liquor was
then not at all acid, but seemed pure water."

From these experiments he concludes "that when a mixture of inflammable
and dephlogisticated air is exploded, in such proportions that the burnt
air is not much phlogisticated, the condensed liquor contains a little
acid which is always of the nitrous kind, whatever substance the
dephlogisticated air is procured from; but if the proportion be such
that the burnt air is almost entirely phlogisticated, the condensed
liquor is not at all acid, but seems pure water, without any addition

These same experiments, which were undertaken to discover the
composition of water, led him to discover also the composition of nitric
acid. He had observed that, in the combustion of hydrogen gas with
common air, the water was slightly tinged with acid, but that this
was not the case when pure oxygen gas was used. Acting upon this
observation, he devised an experiment to determine the nature of this
acid. He constructed an apparatus whereby an electric spark was passed
through a vessel containing common air. After this process had been
carried on for several weeks a small amount of liquid was formed. This
liquid combined with a solution of potash to form common nitre, which
"detonated with charcoal, sparkled when paper impregnated with it was
burned, and gave out nitrous fumes when sulphuric acid was poured on
it." In other words, the liquid was shown to be nitric acid. Now, since
nothing but pure air had been used in the initial experiment, and since
air is composed of nitrogen and oxygen, there seemed no room to doubt
that nitric acid is a combination of nitrogen and oxygen.

This discovery of the nature of nitric acid seems to have been about the
last work of importance that Cavendish did in the field of chemistry,
although almost to the hour of his death he was constantly occupied with
scientific observations. Even in the last moments of his life this habit
asserted itself, according to Lord Brougham. "He died on March 10, 1810,
after a short illness, probably the first, as well as the last, which he
ever suffered. His habit of curious observation continued to the end.
He was desirous of marking the progress of the disease and the gradual
extinction of the vital powers. With these ends in view, that he might
not be disturbed, he desired to be left alone. His servant, returning
sooner than he had wished, was ordered again to leave the chamber of
death, and when he came back a second time he found his master had


While the opulent but diffident Cavendish was making his important
discoveries, another Englishman, a poor country preacher named Joseph
Priestley (1733-1804) was not only rivalling him, but, if anything,
outstripping him in the pursuit of chemical discoveries. In 1761 this
young minister was given a position as tutor in a nonconformist academy
at Warrington, and here, for six years, he was able to pursue his
studies in chemistry and electricity. In 1766, while on a visit to
London, he met Benjamin Franklin, at whose suggestion he published his
History of Electricity. From this time on he made steady progress in
scientific investigations, keeping up his ecclesiastical duties at the
same time. In 1780 he removed to Birmingham, having there for associates
such scientists as James Watt, Boulton, and Erasmus Darwin.

Eleven years later, on the anniversary of the fall of the Bastile in
Paris, a fanatical mob, knowing Priestley's sympathies with the
French revolutionists, attacked his house and chapel, burning both and
destroying a great number of valuable papers and scientific instruments.
Priestley and his family escaped violence by flight, but his most
cherished possessions were destroyed; and three years later he quitted
England forever, removing to the United States, whose struggle for
liberty he had championed. The last ten years of his life were spent
at Northumberland, Pennsylvania, where he continued his scientific

Early in his scientific career Priestley began investigations upon the
"fixed air" of Dr. Black, and, oddly enough, he was stimulated to this
by the same thing that had influenced Black--that is, his residence in
the immediate neighborhood of a brewery. It was during the course of a
series of experiments on this and other gases that he made his greatest
discovery, that of oxygen, or "dephlogisticated air," as he called
it. The story of this important discovery is probably best told in
Priestley's own words:

"There are, I believe, very few maxims in philosophy that have laid
firmer hold upon the mind than that air, meaning atmospheric air, is a
simple elementary substance, indestructible and unalterable, at least as
much so as water is supposed to be. In the course of my inquiries I
was, however, soon satisfied that atmospheric air is not an unalterable
thing; for that, according to my first hypothesis, the phlogiston with
which it becomes loaded from bodies burning in it, and the animals
breathing it, and various other chemical processes, so far alters
and depraves it as to render it altogether unfit for inflammation,
respiration, and other purposes to which it is subservient; and I had
discovered that agitation in the water, the process of vegetation, and
probably other natural processes, restore it to its original purity....

"Having procured a lens of twelve inches diameter and twenty inches
local distance, I proceeded with the greatest alacrity, by the help of
it, to discover what kind of air a great variety of substances would
yield, putting them into the vessel, which I filled with quicksilver,
and kept inverted in a basin of the same .... With this apparatus, after
a variety of experiments.... on the 1st of August, 1774, I endeavored
to extract air from mercurius calcinatus per se; and I presently found
that, by means of this lens, air was expelled from it very readily.
Having got about three or four times as much as the bulk of my
materials, I admitted water to it, and found that it was not imbibed
by it. But what surprised me more than I can express was that a candle
burned in this air with a remarkably vigorous flame, very much like that
enlarged flame with which a candle burns in nitrous oxide, exposed to
iron or liver of sulphur; but as I had got nothing like this remarkable
appearance from any kind of air besides this particular modification of
vitrous air, and I knew no vitrous acid was used in the preparation of
mercurius calcinatus, I was utterly at a loss to account for it."(4)

The "new air" was, of course, oxygen. Priestley at once proceeded to
examine it by a long series of careful experiments, in which, as will
be seen, he discovered most of the remarkable qualities of this gas.
Continuing his description of these experiments, he says:

"The flame of the candle, besides being larger, burned with more
splendor and heat than in that species of nitrous air; and a piece of
red-hot wood sparkled in it, exactly like paper dipped in a solution of
nitre, and it consumed very fast; an experiment that I had never thought
of trying with dephlogisticated nitrous air.

"... I had so little suspicion of the air from the mercurius calcinatus,
etc., being wholesome, that I had not even thought of applying it to
the test of nitrous air; but thinking (as my reader must imagine I
frequently must have done) on the candle burning in it after long
agitation in water, it occurred to me at last to make the experiment;
and, putting one measure of nitrous air to two measures of this air, I
found not only that it was diminished, but that it was diminished quite
as much as common air, and that the redness of the mixture was likewise
equal to a similar mixture of nitrous and common air.... The next day I
was more surprised than ever I had been before with finding that, after
the above-mentioned mixture of nitrous air and the air from mercurius
calcinatus had stood all night,... a candle burned in it, even better
than in common air."

A little later Priestley discovered that "dephlogisticated air... is a
principal element in the composition of acids, and may be extracted by
means of heat from many substances which contain them.... It is likewise
produced by the action of light upon green vegetables; and this seems to
be the chief means employed to preserve the purity of the atmosphere."

This recognition of the important part played by oxygen in the
atmosphere led Priestley to make some experiments upon mice and insects,
and finally upon himself, by inhalations of the pure gas. "The feeling
in my lungs," he said, "was not sensibly different from that of common
air, but I fancied that my breathing felt peculiarly light and easy for
some time afterwards. Who can tell but that in time this pure air may
become a fashionable article in luxury?... Perhaps we may from these
experiments see that though pure dephlogisticated air might be useful as
a medicine, it might not be so proper for us in the usual healthy state
of the body."

This suggestion as to the possible usefulness of oxygen as a medicine
was prophetic. A century later the use of oxygen had become a matter of
routine practice with many physicians. Even in Priestley's own time such
men as Dr. John Hunter expressed their belief in its efficacy in certain
conditions, as we shall see, but its value in medicine was not fully
appreciated until several generations later.

Several years after discovering oxygen Priestley thus summarized its
properties: "It is this ingredient in the atmospheric air that enables
it to support combustion and animal life. By means of it most intense
heat may be produced, and in the purest of it animals will live nearly
five times as long as in an equal quantity of atmospheric air. In
respiration, part of this air, passing the membranes of the lungs,
unites with the blood and imparts to it its florid color, while the
remainder, uniting with phlogiston exhaled from venous blood, forms
mixed air. It is dephlogisticated air combined with water that enables
fishes to live in it."(5)


The discovery of oxygen was the last but most important blow to the
tottering phlogiston theory, though Priestley himself would not admit
it. But before considering the final steps in the overthrow of Stahl's
famous theory and the establishment of modern chemistry, we must review
the work of another great chemist, Karl Wilhelm Scheele (1742-1786), of
Sweden, who discovered oxygen quite independently, although later than
Priestley. In the matter of brilliant discoveries in a brief space of
time Scheele probably eclipsed all his great contemporaries. He had a
veritable genius for interpreting chemical reactions and discovering
new substances, in this respect rivalling Priestley himself. Unlike
Priestley, however, he planned all his experiments along the lines of
definite theories from the beginning, the results obtained being the
logical outcome of a predetermined plan.

Scheele was the son of a merchant of Stralsund, Pomerania, which then
belonged to Sweden. As a boy in school he showed so little aptitude for
the study of languages that he was apprenticed to an apothecary at the
age of fourteen. In this work he became at once greatly interested, and,
when not attending to his duties in the dispensary, he was busy day and
night making experiments or studying books on chemistry. In 1775, still
employed as an apothecary, he moved to Stockholm, and soon after he sent
to Bergman, the leading chemist of Sweden, his first discovery--that of
tartaric acid, which he had isolated from cream of tartar. This was the
beginning of his career of discovery, and from that time on until his
death he sent forth accounts of new discoveries almost uninterruptedly.
Meanwhile he was performing the duties of an ordinary apothecary, and
struggling against poverty. His treatise upon Air and Fire appeared
in 1777. In this remarkable book he tells of his discovery of
oxygen--"empyreal" or "fire-air," as he calls it--which he seems to
have made independently and without ever having heard of the previous
discovery by Priestley. In this book, also, he shows that air is
composed chiefly of oxygen and nitrogen gas.

Early in his experimental career Scheele undertook the solution of
the composition of black oxide of manganese, a substance that had long
puzzled the chemists. He not only succeeded in this, but incidentally in
the course of this series of experiments he discovered oxygen, baryta,
and chlorine, the last of far greater importance, at least commercially,
than the real object of his search. In speaking of the experiment in
which the discovery was made he says:

"When marine (hydrochloric) acid stood over manganese in the cold it
acquired a dark reddish-brown color. As manganese does not give any
colorless solution without uniting with phlogiston (probably meaning
hydrogen), it follows that marine acid can dissolve it without this
principle. But such a solution has a blue or red color. The color is
here more brown than red, the reason being that the very finest portions
of the manganese, which do not sink so easily, swim in the red solution;
for without these fine particles the solution is red, and red mixed with
black is brown. The manganese has here attached itself so loosely to
acidum salis that the water can precipitate it, and this precipitate
behaves like ordinary manganese. When, now, the mixture of manganese and
spiritus salis was set to digest, there arose an effervescence and smell
of aqua regis."(6)

The "effervescence" he refers to was chlorine, which he proceeded to
confine in a suitable vessel and examine more fully. He described it as
having a "quite characteristically suffocating smell," which was very
offensive. He very soon noted the decolorizing or bleaching effects of
this now product, finding that it decolorized flowers, vegetables, and
many other substances.

Commercially this discovery of chlorine was of enormous importance and
the practical application of this new chemical in bleaching cloth soon
supplanted the old process of crofting--that is, bleaching by spreading
the cloth upon the grass. But although Scheele first pointed out the
bleaching quality of his newly discovered gas, it was the French savant,
Berthollet, who, acting upon Scheele's discovery that the new gas would
decolorize vegetables and flowers, was led to suspect that this property
might be turned to account in destroying the color of cloth. In 1785 he
read a paper before the Academy of Sciences of Paris, in which he showed
that bleaching by chlorine was entirely satisfactory, the color but
not the substance of the cloth being affected. He had experimented
previously and found that the chlorine gas was soluble in water and
could thus be made practically available for bleaching purposes. In 1786
James Watt examined specimens of the bleached cloth made by Berthollet,
and upon his return to England first instituted the process of practical
bleaching. His process, however, was not entirely satisfactory, and,
after undergoing various modifications and improvements, it was finally
made thoroughly practicable by Mr. Tennant, who hit upon a compound of
chlorine and lime--the chloride of lime--which was a comparatively cheap
chemical product, and answered the purpose better even than chlorine

To appreciate how momentous this discovery was to cloth manufacturers,
it should be remembered that the old process of bleaching consumed an
entire summer for the whitening of a single piece of linen; the new
process reduced the period to a few hours. To be sure, lime had been
used with fair success previous to Tennant's discovery, but successful
and practical bleaching by a solution of chloride of lime was first made
possible by him and through Scheele's discovery of chlorine.

Until the time of Scheele the great subject of organic chemistry had
remained practically unexplored, but under the touch of his marvellous
inventive genius new methods of isolating and studying animal and
vegetable products were introduced, and a large number of acids and
other organic compounds prepared that had been hitherto unknown. His
explanations of chemical phenomena were based on the phlogiston theory,
in which, like Priestley, he always, believed. Although in error in
this respect, he was, nevertheless, able to make his discoveries with
extremely accurate interpretations. A brief epitome of the list of some
of his more important discoveries conveys some idea, of his fertility of
mind as well as his industry. In 1780 he discovered lactic acid,(7) and
showed that it was the substance that caused the acidity of sour
milk; and in the same year he discovered mucic acid. Next followed the
discovery of tungstic acid, and in 1783 he added to his list of useful
discoveries that of glycerine. Then in rapid succession came his
announcements of the new vegetable products citric, malic, oxalic, and
gallic acids. Scheele not only made the discoveries, but told the
world how he had made them--how any chemist might have made them if
he chose--for he never considered that he had really discovered any
substance until he had made it, decomposed it, and made it again.

His experiments on Prussian blue are most interesting, not only because
of the enormous amount of work involved and the skill he displayed in
his experiments, but because all the time the chemist was handling,
smelling, and even tasting a compound of one of the most deadly poisons,
ignorant of the fact that the substance was a dangerous one to handle.
His escape from injury seems almost miraculous; for his experiments,
which were most elaborate, extended over a considerable period of time,
during which he seems to have handled this chemical with impunity.

While only forty years of age and just at the zenith of his fame,
Scheele was stricken by a fatal illness, probably induced by his
ceaseless labor and exposure. It is gratifying to know, however, that
during the last eight or nine years of his life he had been less bound
down by pecuniary difficulties than before, as Bergman had obtained for
him an annual grant from the Academy. But it was characteristic of the
man that, while devoting one-sixth of the amount of this grant to his
personal wants, the remaining five-sixths was devoted to the expense of
his experiments.


The time was ripe for formulating the correct theory of chemical
composition: it needed but the master hand to mould the materials into
the proper shape. The discoveries in chemistry during the eighteenth
century had been far-reaching and revolutionary in character. A brief
review of these discoveries shows how completely they had subverted
the old ideas of chemical elements and chemical compounds. Of the four
substances earth, air, fire, and water, for many centuries believed
to be elementary bodies, not one has stood the test of the
eighteenth-century chemists. Earth had long since ceased to be regarded
as an element, and water and air had suffered the same fate in this
century. And now at last fire itself, the last of the four "elements"
and the keystone to the phlogiston arch, was shown to be nothing more
than one of the manifestations of the new element, oxygen, and not
"phlogiston" or any other intangible substance.

In this epoch of chemical discoveries England had produced such mental
giants and pioneers in science as Black, Priestley, and Cavendish;
Sweden had given the world Scheele and Bergman, whose work, added to
that of their English confreres, had laid the broad base of chemistry
as a science; but it was for France to produce a man who gave the
final touches to the broad but rough workmanship of its foundation,
and establish it as the science of modern chemistry. It was for Antoine
Laurent Lavoisier (1743-1794) to gather together, interpret correctly,
rename, and classify the wealth of facts that his immediate predecessors
and contemporaries had given to the world.

The attitude of the mother-countries towards these illustrious sons is
an interesting piece of history. Sweden honored and rewarded Scheele
and Bergman for their efforts; England received the intellectuality of
Cavendish with less appreciation than the Continent, and a fanatical mob
drove Priestley out of the country; while France, by sending Lavoisier
to the guillotine, demonstrated how dangerous it was, at that time
at least, for an intelligent Frenchman to serve his fellowman and his
country well.

"The revolution brought about by Lavoisier in science," says Hoefer,
"coincides by a singular act of destiny with another revolution, much
greater indeed, going on then in the political and social world. Both
happened on the same soil, at the same epoch, among the same people;
and both marked the commencement of a new era in their respective

Lavoisier was born in Paris, and being the son of an opulent family,
was educated under the instruction of the best teachers of the day. With
Lacaille he studied mathematics and astronomy; with Jussieu, botany;
and, finally, chemistry under Rouelle. His first work of importance was
a paper on the practical illumination of the streets of Paris, for which
a prize had been offered by M. de Sartine, the chief of police. This
prize was not awarded to Lavoisier, but his suggestions were of such
importance that the king directed that a gold medal be bestowed upon the
young author at the public sitting of the Academy in April, 1776. Two
years later, at the age of thirty-five, Lavoisier was admitted a member
of the Academy.

In this same year he began to devote himself almost exclusively to
chemical inquiries, and established a laboratory in his home, fitted
with all manner of costly apparatus and chemicals. Here he was in
constant communication with the great men of science of Paris, to all of
whom his doors were thrown open. One of his first undertakings in this
laboratory was to demonstrate that water could not be converted into
earth by repeated distillations, as was generally advocated; and to show
also that there was no foundation to the existing belief that it was
possible to convert water into a gas so "elastic" as to pass through
the pores of a vessel. He demonstrated the fallaciousness of both these
theories in 1768-1769 by elaborate experiments, a single investigation
of this series occupying one hundred and one days.

In 1771 he gave the first blow to the phlogiston theory by his
experiments on the calcination of metals. It will be recalled that one
basis for the belief in phlogiston was the fact that when a metal was
calcined it was converted into an ash, giving up its "phlogiston" in the
process. To restore the metal, it was necessary to add some substance
such as wheat or charcoal to the ash. Lavoisier, in examining this
process of restoration, found that there was always evolved a great
quantity of "air," which he supposed to be "fixed air" or carbonic
acid--the same that escapes in effervescence of alkalies and calcareous
earths, and in the fermentation of liquors. He then examined the process
of calcination, whereby the phlogiston of the metal was supposed to
have been drawn off. But far from finding that phlogiston or any other
substance had been driven off, he found that something had been taken
on: that the metal "absorbed air," and that the increased weight of the
metal corresponded to the amount of air "absorbed." Meanwhile he
was within grasp of two great discoveries, that of oxygen and of the
composition of the air, which Priestley made some two years later.

The next important inquiry of this great Frenchman was as to the
composition of diamonds. With the great lens of Tschirnhausen belonging
to the Academy he succeeded in burning up several diamonds, regardless
of expense, which, thanks to his inheritance, he could ignore. In this
process he found that a gas was given off which precipitated lime from
water, and proved to be carbonic acid. Observing this, and experimenting
with other substances known to give off carbonic acid in the same
manner, he was evidently impressed with the now well-known fact that
diamond and charcoal are chemically the same. But if he did really
believe it, he was cautious in expressing his belief fully. "We should
never have expected," he says, "to find any relation between charcoal
and diamond, and it would be unreasonable to push this analogy too far;
it only exists because both substances seem to be properly ranged in the
class of combustible bodies, and because they are of all these bodies
the most fixed when kept from contact with air."

As we have seen, Priestley, in 1774, had discovered oxygen, or
"dephlogisticated air." Four years later Lavoisier first advanced his
theory that this element discovered by Priestley was the universal
acidifying or oxygenating principle, which, when combined with charcoal
or carbon, formed carbonic acid; when combined with sulphur, formed
sulphuric (or vitriolic) acid; with nitrogen, formed nitric acid,
etc., and when combined with the metals formed oxides, or calcides.
Furthermore, he postulated the theory that combustion was not due to any
such illusive thing as "phlogiston," since this did not exist, and it
seemed to him that the phenomena of combustion heretofore attributed to
phlogiston could be explained by the action of the new element oxygen
and heat. This was the final blow to the phlogiston theory, which,
although it had been tottering for some time, had not been completely

In 1787 Lavoisier, in conjunction with Guyon de Morveau, Berthollet,
and Fourcroy, introduced the reform in chemical nomenclature which until
then had remained practically unchanged since alchemical days. Such
expressions as "dephlogisticated" and "phlogisticated" would obviously
have little meaning to a generation who were no longer to believe in
the existence of phlogiston. It was appropriate that a revolution in
chemical thought should be accompanied by a corresponding revolution in
chemical names, and to Lavoisier belongs chiefly the credit of bringing
about this revolution. In his Elements of Chemistry he made use of this
new nomenclature, and it seemed so clearly an improvement over the
old that the scientific world hastened to adopt it. In this connection
Lavoisier says: "We have, therefore, laid aside the expression metallic
calx altogether, and have substituted in its place the word oxide. By
this it may be seen that the language we have adopted is both copious
and expressive. The first or lowest degree of oxygenation in bodies
converts them into oxides; a second degree of additional oxygenation
constitutes the class of acids of which the specific names drawn from
their particular bases terminate in ous, as in the nitrous and the
sulphurous acids. The third degree of oxygenation changes these into the
species of acids distinguished by the termination in ic, as the nitric
and sulphuric acids; and, lastly, we can express a fourth or higher
degree of oxygenation by adding the word oxygenated to the name of the
acid, as has already been done with oxygenated muriatic acid."(9)

This new work when given to the world was not merely an epoch-making
book; it was revolutionary. It not only discarded phlogiston altogether,
but set forth that metals are simple elements, not compounds of "earth"
and "phlogiston." It upheld Cavendish's demonstration that water itself,
like air, is a compound of oxygen with another element. In short, it was
scientific chemistry, in the modern acceptance of the term.

Lavoisier's observations on combustion are at once important and
interesting: "Combustion," he says, "... is the decomposition of oxygen
produced by a combustible body. The oxygen which forms the base of this
gas is absorbed by and enters into combination with the burning body,
while the caloric and light are set free. Every combustion necessarily
supposes oxygenation; whereas, on the contrary, every oxygenation
does not necessarily imply concomitant combustion; because combustion
properly so called cannot take place without disengagement of caloric
and light. Before combustion can take place, it is necessary that the
base of oxygen gas should have greater affinity to the combustible body
than it has to caloric; and this elective attraction, to use Bergman's
expression, can only take place at a certain degree of temperature which
is different for each combustible substance; hence the necessity of
giving the first motion or beginning to every combustion by the approach
of a heated body. This necessity of heating any body we mean to burn
depends upon certain considerations which have not hitherto been
attended to by any natural philosopher, for which reason I shall enlarge
a little upon the subject in this place:

"Nature is at present in a state of equilibrium, which cannot have been
attained until all the spontaneous combustions or oxygenations possible
in an ordinary degree of temperature had taken place.... To illustrate
this abstract view of the matter by example: Let us suppose the usual
temperature of the earth a little changed, and it is raised only to the
degree of boiling water; it is evident that in this case phosphorus,
which is combustible in a considerably lower degree of temperature,
would no longer exist in nature in its pure and simple state, but would
always be procured in its acid or oxygenated state, and its radical
would become one of the substances unknown to chemistry. By gradually
increasing the temperature of the earth, the same circumstance would
successively happen to all the bodies capable of combustion; and, at
the last, every possible combustion having taken place, there would
no longer exist any combustible body whatever, and every substance
susceptible of the operation would be oxygenated and consequently

"There cannot, therefore, exist, as far as relates to us, any
combustible body but such as are non-combustible at the ordinary
temperature of the earth, or, what is the same thing in other words,
that it is essential to the nature of every combustible body not to
possess the property of combustion unless heated, or raised to a degree
of temperature at which its combustion naturally takes place. When this
degree is once produced, combustion commences, and the caloric which
is disengaged by the decomposition of the oxygen gas keeps up the
temperature which is necessary for continuing combustion. When this is
not the case--that is, when the disengaged caloric is not sufficient
for keeping up the necessary temperature--the combustion ceases. This
circumstance is expressed in the common language by saying that a body
burns ill or with difficulty."(10)

It needed the genius of such a man as Lavoisier to complete the
refutation of the false but firmly grounded phlogiston theory, and
against such a book as his Elements of Chemistry the feeble weapons of
the supporters of the phlogiston theory were hurled in vain.

But while chemists, as a class, had become converts to the new chemistry
before the end of the century, one man, Dr. Priestley, whose work had
done so much to found it, remained unconverted. In this, as in all his
life-work, he showed himself to be a most remarkable man. Davy said of
him, a generation later, that no other person ever discovered so many
new and curious substances as he; yet to the last he was only an amateur
in science, his profession, as we know, being the ministry. There is
hardly another case in history of a man not a specialist in science
accomplishing so much in original research as did this chemist,
physiologist, electrician; the mathematician, logician, and moralist;
the theologian, mental philosopher, and political economist. He took
all knowledge for his field; but how he found time for his numberless
researches and multifarious writings, along with his every-day duties,
must ever remain a mystery to ordinary mortals.

That this marvellously receptive, flexible mind should have refused
acceptance to the clearly logical doctrines of the new chemistry seems
equally inexplicable. But so it was. To the very last, after all his
friends had capitulated, Priestley kept up the fight. From America he
sent out his last defy to the enemy, in 1800, in a brochure entitled
"The Doctrine of Phlogiston Upheld," etc. In the mind of its author it
was little less than a paean of victory; but all the world beside knew
that it was the swan-song of the doctrine of phlogiston. Despite the
defiance of this single warrior the battle was really lost and won,
and as the century closed "antiphlogistic" chemistry had practical
possession of the field.



Small beginnings as have great endings--sometimes. As a case in
point, note what came of the small, original effort of a self-trained
back-country Quaker youth named John Dalton, who along towards the close
of the eighteenth century became interested in the weather, and was
led to construct and use a crude water-gauge to test the amount of the
rainfall. The simple experiments thus inaugurated led to no fewer than
two hundred thousand recorded observations regarding the weather,
which formed the basis for some of the most epochal discoveries in
meteorology, as we have seen. But this was only a beginning. The simple
rain-gauge pointed the way to the most important generalization of
the nineteenth century in a field of science with which, to the casual
observer, it might seem to have no alliance whatever. The wonderful
theory of atoms, on which the whole gigantic structure of modern
chemistry is founded, was the logical outgrowth, in the mind of John
Dalton, of those early studies in meteorology.

The way it happened was this: From studying the rainfall, Dalton turned
naturally to the complementary process of evaporation. He was soon led
to believe that vapor exists, in the atmosphere as an independent gas.
But since two bodies cannot occupy the same space at the same time,
this implies that the various atmospheric gases are really composed of
discrete particles. These ultimate particles are so small that we cannot
see them--cannot, indeed, more than vaguely imagine them--yet each
particle of vapor, for example, is just as much a portion of water as if
it were a drop out of the ocean, or, for that matter, the ocean itself.
But, again, water is a compound substance, for it may be separated, as
Cavendish has shown, into the two elementary substances hydrogen and
oxygen. Hence the atom of water must be composed of two lesser atoms
joined together. Imagine an atom of hydrogen and one of oxygen. Unite
them, and we have an atom of water; sever them, and the water no longer
exists; but whether united or separate the atoms of hydrogen and of
oxygen remain hydrogen and oxygen and nothing else. Differently mixed
together or united, atoms produce different gross substances; but the
elementary atoms never change their chemical nature--their distinct

It was about the year 1803 that Dalton first gained a full grasp of the
conception of the chemical atom. At once he saw that the hypothesis,
if true, furnished a marvellous key to secrets of matter hitherto
insoluble--questions relating to the relative proportions of the atoms
themselves. It is known, for example, that a certain bulk of hydrogen
gas unites with a certain bulk of oxygen gas to form water. If it be
true that this combination consists essentially of the union of atoms
one with another (each single atom of hydrogen united to a single atom
of oxygen), then the relative weights of the original masses of hydrogen
and of oxygen must be also the relative weights of each of their
respective atoms. If one pound of hydrogen unites with five and one-half
pounds of oxygen (as, according to Dalton's experiments, it did), then
the weight of the oxygen atom must be five and one-half times that of
the hydrogen atom. Other compounds may plainly be tested in the same
way. Dalton made numerous tests before he published his theory. He found
that hydrogen enters into compounds in smaller proportions than any
other element known to him, and so, for convenience, determined to take
the weight of the hydrogen atom as unity. The atomic weight of oxygen
then becomes (as given in Dalton's first table of 1803) 5.5; that of
water (hydrogen plus oxygen) being of course 6.5. The atomic weights of
about a score of substances are given in Dalton's first paper, which
was read before the Literary and Philosophical Society of Manchester,
October 21, 1803. I wonder if Dalton himself, great and acute intellect
though he had, suspected, when he read that paper, that he was
inaugurating one of the most fertile movements ever entered on in the
whole history of science?

Be that as it may, it is certain enough that Dalton's contemporaries
were at first little impressed with the novel atomic theory. Just at
this time, as it chanced, a dispute was waging in the field of chemistry
regarding a matter of empirical fact which must necessarily be settled
before such a theory as that of Dalton could even hope for a bearing.
This was the question whether or not chemical elements unite with one
another always in definite proportions. Berthollet, the great co-worker
with Lavoisier, and now the most authoritative of living chemists,
contended that substances combine in almost indefinitely graded
proportions between fixed extremes. He held that solution is really a
form of chemical combination--a position which, if accepted, left no
room for argument.

But this contention of the master was most actively disputed, in
particular by Louis Joseph Proust, and all chemists of repute were
obliged to take sides with one or the other. For a time the authority of
Berthollet held out against the facts, but at last accumulated evidence
told for Proust and his followers, and towards the close of the first
decade of our century it came to be generally conceded that chemical
elements combine with one another in fixed and definite proportions.

More than that. As the analysts were led to weigh carefully the
quantities of combining elements, it was observed that the proportions
are not only definite, but that they bear a very curious relation to one
another. If element A combines with two different proportions of element
B to form two compounds, it appears that the weight of the larger
quantity of B is an exact multiple of that of the smaller quantity. This
curious relation was noticed by Dr. Wollaston, one of the most accurate
of observers, and a little later it was confirmed by Johan Jakob
Berzelius, the great Swedish chemist, who was to be a dominating
influence in the chemical world for a generation to come. But this
combination of elements in numerical proportions was exactly what Dalton
had noticed as early as 1802, and what bad led him directly to the
atomic weights. So the confirmation of this essential point by chemists
of such authority gave the strongest confirmation to the atomic theory.

During these same years the rising authority of the French chemical
world, Joseph Louis Gay-Lussac, was conducting experiments with gases,
which he had undertaken at first in conjunction with Humboldt, but which
later on were conducted independently. In 1809, the next year after
the publication of the first volume of Dalton's New System of Chemical
Philosophy, Gay-Lussac published the results of his observations, and
among other things brought out the remarkable fact that gases, under
the same conditions as to temperature and pressure, combine always in
definite numerical proportions as to volume. Exactly two volumes of
hydrogen, for example, combine with one volume of oxygen to form water.
Moreover, the resulting compound gas always bears a simple relation to
the combining volumes. In the case just cited, the union of two volumes
of hydrogen and one of oxygen results in precisely two volumes of water

Naturally enough, the champions of the atomic theory seized upon
these observations of Gay-Lussac as lending strong support to their
hypothesis--all of them, that is, but the curiously self-reliant and
self-sufficient author of the atomic theory himself, who declined
to accept the observations of the French chemist as valid. Yet the
observations of Gay-Lussac were correct, as countless chemists since
then have demonstrated anew, and his theory of combination by volumes
became one of the foundation-stones of the atomic theory, despite the
opposition of the author of that theory.

The true explanation of Gay-Lussac's law of combination by volumes was
thought out almost immediately by an Italian savant, Amadeo, Avogadro,
and expressed in terms of the atomic theory. The fact must be, said
Avogadro, that under similar physical conditions every form of gas
contains exactly the same number of ultimate particles in a given
volume. Each of these ultimate physical particles may be composed of two
or more atoms (as in the case of water vapor), but such a compound atom
conducts itself as if it were a simple and indivisible atom, as regards
the amount of space that separates it from its fellows under given
conditions of pressure and temperature. The compound atom, composed
of two or more elementary atoms, Avogadro proposed to distinguish, for
purposes of convenience, by the name molecule. It is to the molecule,
considered as the unit of physical structure, that Avogadro's law

This vastly important distinction between atoms and molecules, implied
in the law just expressed, was published in 1811. Four years later, the
famous French physicist Ampere outlined a similar theory, and utilized
the law in his mathematical calculations. And with that the law of
Avogadro dropped out of sight for a full generation. Little suspecting
that it was the very key to the inner mysteries of the atoms for which
they were seeking, the chemists of the time cast it aside, and let it
fade from the memory of their science.

This, however, was not strange, for of course the law of Avogadro is
based on the atomic theory, and in 1811 the atomic theory was itself
still being weighed in the balance. The law of multiple proportions
found general acceptance as an empirical fact; but many of the leading
lights of chemistry still looked askance at Dalton's explanation of this
law. Thus Wollaston, though from the first he inclined to acceptance of
the Daltonian view, cautiously suggested that it would be well to use
the non-committal word "equivalent" instead of "atom"; and Davy, for
a similar reason, in his book of 1812, speaks only of "proportions,"
binding himself to no theory as to what might be the nature of these

At least two great chemists of the time, however, adopted the atomic
view with less reservation. One of these was Thomas Thomson, professor
at Edinburgh, who, in 1807, had given an outline of Dalton's theory in
a widely circulated book, which first brought the theory to the general
attention of the chemical world. The other and even more noted advocate
of the atomic theory was Johan Jakob Berzelius. This great Swedish
chemist at once set to work to put the atomic theory to such tests as
might be applied in the laboratory. He was an analyst of the utmost
skill, and for years he devoted himself to the determination of the
combining weights, "equivalents" or "proportions," of the different
elements. These determinations, in so far as they were accurately made,
were simple expressions of empirical facts, independent of any theory;
but gradually it became more and more plain that these facts all
harmonize with the atomic theory of Dalton. So by common consent the
proportionate combining weights of the elements came to be known as
atomic weights--the name Dalton had given them from the first--and
the tangible conception of the chemical atom as a body of definite
constitution and weight gained steadily in favor.

From the outset the idea had had the utmost tangibility in the mind of
Dalton. He had all along represented the different atoms by geometrical
symbols--as a circle for oxygen, a circle enclosing a dot for hydrogen,
and the like--and had represented compounds by placing these symbols of
the elements in juxtaposition. Berzelius proposed to improve upon this
method by substituting for the geometrical symbol the initial of the
Latin name of the element represented--O for oxygen, H for hydrogen, and
so on--a numerical coefficient to follow the letter as an indication of
the number of atoms present in any given compound. This simple system
soon gained general acceptance, and with slight modifications it is
still universally employed. Every school-boy now is aware that H2O is
the chemical way of expressing the union of two atoms of hydrogen with
one of oxygen to form a molecule of water. But such a formula would have
had no meaning for the wisest chemist before the day of Berzelius.

The universal fame of the great Swedish authority served to give general
currency to his symbols and atomic weights, and the new point of view
thus developed led presently to two important discoveries which removed
the last lingering doubts as to the validity of the atomic theory. In
1819 two French physicists, Dulong and Petit, while experimenting with
heat, discovered that the specific heats of solids (that is to say, the
amount of heat required to raise the temperature of a given mass to a
given degree) vary inversely as their atomic weights. In the same year
Eilhard Mitscherlich, a German investigator, observed that compounds
having the same number of atoms to the molecule are disposed to form the
same angles of crystallization--a property which he called isomorphism.

Here, then, were two utterly novel and independent sets of empirical
facts which harmonize strangely with the supposition that substances are
composed of chemical atoms of a determinate weight. This surely could
not be coincidence--it tells of law. And so as soon as the claims of
Dulong and Petit and of Mitscherlich had been substantiated by other
observers, the laws of the specific heat of atoms, and of isomorphism,
took their place as new levers of chemical science. With the aid of
these new tools an impregnable breastwork of facts was soon piled about
the atomic theory. And John Dalton, the author of that theory, plain,
provincial Quaker, working on to the end in semi-retirement, became
known to all the world and for all time as a master of masters.


During those early years of the nineteenth century, when Dalton was
grinding away at chemical fact and theory in his obscure Manchester
laboratory, another Englishman held the attention of the chemical world
with a series of the most brilliant and widely heralded researches. This
was Humphry Davy, a young man who had conic to London in 1801, at the
instance of Count Rumford, to assume the chair of chemical philosophy in
the Royal Institution, which the famous American had just founded.

Here, under Davy's direction, the largest voltaic battery yet
constructed had been put in operation, and with its aid the brilliant
young experimenter was expected almost to perform miracles. And indeed
he scarcely disappointed the expectation, for with the aid of his
battery he transformed so familiar a substance as common potash into
a metal which was not only so light that it floated on water, but
possessed the seemingly miraculous property of bursting into flames as
soon as it came in contact with that fire-quenching liquid. If this
were not a miracle, it had for the popular eye all the appearance of the

What Davy really had done was to decompose the potash, which hitherto
had been supposed to be elementary, liberating its oxygen, and thus
isolating its metallic base, which he named potassium. The same
thing was done with soda, and the closely similar metal sodium was
discovered--metals of a unique type, possessed of a strange avidity for
oxygen, and capable of seizing on it even when it is bound up in the
molecules of water. Considered as mere curiosities, these discoveries
were interesting, but aside from that they were of great theoretical
importance, because they showed the compound nature of some familiar
chemicals that had been regarded as elements. Several other elementary
earths met the same fate when subjected to the electrical influence; the
metals barium, calcium, and strontium being thus discovered. Thereafter
Davy always referred to the supposed elementary substances (including
oxygen, hydrogen, and the rest) as "unde-compounded" bodies. These
resist all present efforts to decompose them, but how can one know what
might not happen were they subjected to an influence, perhaps some day
to be discovered, which exceeds the battery in power as the battery
exceeds the blowpipe?

Another and even more important theoretical result that flowed from
Davy's experiments during this first decade of the century was the
proof that no elementary substances other than hydrogen and oxygen are
produced when pure water is decomposed by the electric current. It was
early noticed by Davy and others that when a strong current is passed
through water, alkalies appear at one pole of the battery and acids at
the other, and this though the water used were absolutely pure. This
seemingly told of the creation of elements--a transmutation but one step
removed from the creation of matter itself--under the influence of the
new "force." It was one of Davy's greatest triumphs to prove, in the
series of experiments recorded in his famous Bakerian lecture of 1806,
that the alleged creation of elements did not take place, the substances
found at the poles of the battery having been dissolved from the walls
of the vessels in which the water experimented upon had been placed.
Thus the same implement which had served to give a certain philosophical
warrant to the fading dreams of alchemy banished those dreams
peremptorily from the domain of present science.

"As early as 1800," writes Davy, "I had found that when separate
portions of distilled water, filling two glass tubes, connected by moist
bladders, or any moist animal or vegetable substances, were submitted
to the electrical action of the pile of Volta by means of gold wires,
a nitro-muriatic solution of gold appeared in the tube containing the
positive wire, or the wire transmitting the electricity, and a solution
of soda in the opposite tube; but I soon ascertained that the muriatic
acid owed its existence to the animal or vegetable matters employed;
for when the same fibres of cotton were made use of in successive
experiments, and washed after every process in a weak solution of nitric
acid, the water in the apparatus containing them, though acted on for
a great length of time with a very strong power, at last produced no
effects upon nitrate of silver.

"In cases when I had procured much soda, the glass at its point of
contact with the wire seemed considerably corroded; and I was confirmed
in my idea of referring the production of the alkali principally to
this source, by finding that no fixed saline matter could be obtained
by electrifying distilled water in a single agate cup from two points of
platina with the Voltaic battery.

"Mr. Sylvester, however, in a paper published in Mr. Nicholson's journal
for last August, states that though no fixed alkali or muriatic acid
appears when a single vessel is employed, yet that they are both formed
when two vessels are used. And to do away with all objections with
regard to vegetable substances or glass, he conducted his process in
a vessel made of baked tobacco-pipe clay inserted in a crucible of
platina. I have no doubt of the correctness of his results; but the
conclusion appears objectionable. He conceives, that he obtained fixed
alkali, because the fluid after being heated and evaporated left a
matter that tinged turmeric brown, which would have happened had it
been lime, a substance that exists in considerable quantities in all
pipe-clay; and even allowing the presence of fixed alkali, the materials
employed for the manufacture of tobacco-pipes are not at all such as to
exclude the combinations of this substance.

"I resumed the inquiry; I procured small cylindrical cups of agate of
the capacity of about one-quarter of a cubic inch each. They were
boiled for some hours in distilled water, and a piece of very white and
transparent amianthus that had been treated in the same way was made
then to connect together; they were filled with distilled water and
exposed by means of two platina wires to a current of electricity, from
one hundred and fifty pairs of plates of copper and zinc four inches
square, made active by means of solution of alum. After forty-eight
hours the process was examined: Paper tinged with litmus plunged into
the tube containing the transmitting or positive wire was immediately
strongly reddened. Paper colored by turmeric introduced into the other
tube had its color much deepened; the acid matter gave a very slight
degree of turgidness to solution of nitrate of soda. The fluid that
affected turmeric retained this property after being strongly
boiled; and it appeared more vivid as the quantity became reduced by
evaporation; carbonate of ammonia was mixed with it, and the whole
dried and exposed to a strong heat; a minute quantity of white matter
remained, which, as far as my examinations could go, had the properties
of carbonate of soda. I compared it with similar minute portions of
the pure carbonates of potash, and similar minute portions of the pure
carbonates of potash and soda. It was not so deliquescent as the former
of these bodies, and it formed a salt with nitric acid, which, like
nitrate of soda, soon attracted moisture from a damp atmosphere and
became fluid.

"This result was unexpected, but it was far from convincing me that the
substances which were obtained were generated. In a similar process with
glass tubes, carried on under exactly the same circumstances and for
the same time, I obtained a quantity of alkali which must have been more
than twenty times greater, but no traces of muriatic acid. There was
much probability that the agate contained some minute portion of saline
matter, not easily detected by chemical analysis, either in combination
or intimate cohesion in its pores. To determine this, I repeated this a
second, a third, and a fourth time. In the second experiment turbidness
was still produced by a solution of nitrate of silver in the tube
containing the acid, but it was less distinct; in the third process
it was barely perceptible; and in the fourth process the two fluids
remained perfectly clear after the mixture. The quantity of alkaline
matter diminished in every operation; and in the last process, though
the battery had been kept in great activity for three days, the fluid
possessed, in a very slight degree, only the power of acting on paper
tinged with turmeric; but its alkaline property was very sensible to
litmus paper slightly reddened, which is a much more delicate test;
and after evaporation and the process by carbonate of ammonia, a barely
perceptible quantity of fixed alkali was still left. The acid matter in
the other tube was abundant; its taste was sour; it smelled like water
over which large quantities of nitrous gas have been long kept; it did
not effect solution of muriate of barytes; and a drop of it placed
upon a polished plate of silver left, after evaporation, a black stain,
precisely similar to that produced by extremely diluted nitrous acid.

"After these results I could no longer doubt that some saline matter
existing in the agate tubes had been the source of the acid matter
capable of precipitating nitrate of silver and much of the alkali. Four
additional repetitions of the process, however, convinced me that there
was likewise some other cause for the presence of this last substance;
for it continued to appear to the last in quantities sufficiently
distinguishable, and apparently equal in every case. I had used every
precaution, I had included the tube in glass vessels out of the reach of
the circulating air; all the acting materials had been repeatedly washed
with distilled water; and no part of them in contact with the fluid had
been touched by the fingers.

"The only substance that I could now conceive as furnishing the fixed
alkali was the water itself. This water appeared pure by the tests of
nitrate of silver and muriate of barytes; but potash of soda, as is
well known, rises in small quantities in rapid distillation; and the
New River water which I made use of contains animal and vegetable
impurities, which it was easy to conceive might furnish neutral
salts capable of being carried over in vivid ebullition."(1) Further
experiment proved the correctness of this inference, and the last doubt
as to the origin of the puzzling chemical was dispelled.

Though the presence of the alkalies and acids in the water was
explained, however, their respective migrations to the negative and
positive poles of the battery remained to be accounted for. Davy's
classical explanation assumed that different elements differ among
themselves as to their electrical properties, some being positively,
others negatively, electrified. Electricity and "chemical affinity," he
said, apparently are manifestations of the same force, acting in the one
case on masses, in the other on particles. Electro-positive particles
unite with electro-negative particles to form chemical compounds, in
virtue of the familiar principle that opposite electricities attract
one another. When compounds are decomposed by the battery, this mutual
attraction is overcome by the stronger attraction of the poles of the
battery itself.

This theory of binary composition of all chemical compounds, through the
union of electro-positive and electro-negative atoms or molecules,
was extended by Berzelius, and made the basis of his famous system of
theoretical chemistry. This theory held that all inorganic compounds,
however complex their composition, are essentially composed of such
binary combinations. For many years this view enjoyed almost undisputed
sway. It received what seemed strong confirmation when Faraday showed
the definite connection between the amount of electricity employed and
the amount of decomposition produced in the so-called electrolyte. But
its claims were really much too comprehensive, as subsequent discoveries


When Berzelius first promulgated his binary theory he was careful to
restrict its unmodified application to the compounds of the inorganic
world. At that time, and for a long time thereafter, it was supposed
that substances of organic nature had some properties that kept them
aloof from the domain of inorganic chemistry. It was little doubted
that a so-called "vital force" operated here, replacing or modifying the
action of ordinary "chemical affinity." It was, indeed, admitted that
organic compounds are composed of familiar elements--chiefly carbon,
oxygen, hydrogen, and nitrogen; but these elements were supposed to
be united in ways that could not be imitated in the domain of the
non-living. It was regarded almost as an axiom of chemistry that
no organic compound whatever could be put together from its
elements--synthesized--in the laboratory. To effect the synthesis of
even the simplest organic compound, it was thought that the "vital
force" must be in operation.

Therefore a veritable sensation was created in the chemical world
when, in the year 1828, it was announced that the young German chemist,
Friedrich Wohler, formerly pupil of Berzelius, and already known as a
coming master, had actually synthesized the well-known organic product
urea in his laboratory at Sacrow. The "exception which proves the rule"
is something never heard of in the domain of logical science. Natural
law knows no exceptions. So the synthesis of a single organic compound
sufficed at a blow to break down the chemical barrier which the
imagination of the fathers of the science had erected between animate
and inanimate nature. Thenceforth the philosophical chemist would
regard the plant and animal organisms as chemical laboratories in which
conditions are peculiarly favorable for building up complex compounds of
a few familiar elements, under the operation of universal chemical laws.
The chimera "vital force" could no longer gain recognition in the domain
of chemistry.

Now a wave of interest in organic chemistry swept over the chemical
world, and soon the study of carbon compounds became as much the fashion
as electrochemistry had been in the, preceding generation.

Foremost among the workers who rendered this epoch of organic chemistry
memorable were Justus Liebig in Germany and Jean Baptiste Andre Dumas
in France, and their respective pupils, Charles Frederic Gerhardt and
Augustus Laurent. Wohler, too, must be named in the same breath, as also
must Louis Pasteur, who, though somewhat younger than the others, came
upon the scene in time to take chief part in the most important of the
controversies that grew out of their labors.

Several years earlier than this the way had been paved for the study
of organic substances by Gay-Lussac's discovery, made in 1815, that a
certain compound of carbon and nitrogen, which he named cyanogen, has a
peculiar degree of stability which enables it to retain its identity and
enter into chemical relations after the manner of a simple body. A year
later Ampere discovered that nitrogen and hydrogen, when combined in
certain proportions to form what he called ammonium, have the same
property. Berzelius had seized upon this discovery of the compound
radical, as it was called, because it seemed to lend aid to his
dualistic theory. He conceived the idea that all organic compounds
are binary unions of various compound radicals with an atom of oxygen,
announcing this theory in 1818. Ten years later, Liebig and Wohler
undertook a joint investigation which resulted in proving that compound
radicals are indeed very abundant among organic substances. Thus the
theory of Berzelius seemed to be substantiated, and organic chemistry
came to be defined as the chemistry of compound radicals.

But even in the day of its seeming triumph the dualistic theory
was destined to receive a rude shock. This came about through the
investigations of Dumas, who proved that in a certain organic substance
an atom of hydrogen may be removed and an atom of chlorine substituted
in its place without destroying the integrity of the original
compound--much as a child might substitute one block for another in
its play-house. Such a substitution would be quite consistent with the
dualistic theory, were it not for the very essential fact that hydrogen
is a powerfully electro-positive element, while chlorine is as strongly
electro-negative. Hence the compound radical which united successively
with these two elements must itself be at one time electro-positive, at
another electro-negative--a seeming inconsistency which threw the entire
Berzelian theory into disfavor.

In its place there was elaborated, chiefly through the efforts of
Laurent and Gerhardt, a conception of the molecule as a unitary
structure, built up through the aggregation of various atoms, in
accordance with "elective affinities" whose nature is not yet understood
A doctrine of "nuclei" and a doctrine of "types" of molecular structure
were much exploited, and, like the doctrine of compound radicals, became
useful as aids to memory and guides for the analyst, indicating some of
the plans of molecular construction, though by no means penetrating the
mysteries of chemical affinity. They are classifications rather than
explanations of chemical unions. But at least they served an important
purpose in giving definiteness to the idea of a molecular structure
built of atoms as the basis of all substances. Now at last the word
molecule came to have a distinct meaning, as distinct from "atom," in
the minds of the generality of chemists, as it had had for Avogadro a
third of a century before. Avogadro's hypothesis that there are equal
numbers of these molecules in equal volumes of gases, under fixed
conditions, was revived by Gerhardt, and a little later, under the
championship of Cannizzaro, was exalted to the plane of a fixed law.
Thenceforth the conception of the molecule was to be as dominant a
thought in chemistry as the idea of the atom had become in a previous


Of course the atom itself was in no sense displaced, but Avogadro's law
soon made it plain that the atom had often usurped territory that
did not really belong to it. In many cases the chemists had supposed
themselves dealing with atoms as units where the true unit was the
molecule. In the case of elementary gases, such as hydrogen and oxygen,
for example, the law of equal numbers of molecules in equal spaces made
it clear that the atoms do not exist isolated, as had been supposed.
Since two volumes of hydrogen unite with one volume of oxygen to form
two volumes of water vapor, the simplest mathematics show, in the light
of Avogadro's law, not only that each molecule of water must contain two
hydrogen atoms (a point previously in dispute), but that the original
molecules of hydrogen and oxygen must have been composed in each case of
two atoms---else how could one volume of oxygen supply an atom for every
molecule of two volumes of water?

What, then, does this imply? Why, that the elementary atom has
an avidity for other atoms, a longing for companionship, an
"affinity"--call it what you will--which is bound to be satisfied if
other atoms are in the neighborhood. Placed solely among atoms of its
own kind, the oxygen atom seizes on a fellow oxygen atom, and in all
their mad dancings these two mates cling together--possibly revolving
about each other in miniature planetary orbits. Precisely the same thing
occurs among the hydrogen atoms. But now suppose the various pairs
of oxygen atoms come near other pairs of hydrogen atoms (under proper
conditions which need not detain us here), then each oxygen atom loses
its attachment for its fellow, and flings itself madly into the circuit
of one of the hydrogen couplets, and--presto!--there are only two
molecules for every three there were before, and free oxygen and
hydrogen have become water. The whole process, stated in chemical
phraseology, is summed up in the statement that under the given
conditions the oxygen atoms had a greater affinity for the hydrogen
atoms than for one another.

As chemists studied the actions of various kinds of atoms, in regard
to their unions with one another to form molecules, it gradually dawned
upon them that not all elements are satisfied with the same number of
companions. Some elements ask only one, and refuse to take more; while
others link themselves, when occasion offers, with two, three, four, or
more. Thus we saw that oxygen forsook a single atom of its own kind
and linked itself with two atoms of hydrogen. Clearly, then, the oxygen
atom, like a creature with two hands, is able to clutch two other atoms.
But we have no proof that under any circumstances it could hold more
than two. Its affinities seem satisfied when it has two bonds. But,
on the other hand, the atom of nitrogen is able to hold three atoms
of hydrogen, and does so in the molecule of ammonium (NH3); while the
carbon atom can hold four atoms of hydrogen or two atoms of oxygen.

Evidently, then, one atom is not always equivalent to another atom of
a different kind in combining powers. A recognition of this fact by
Frankland about 1852, and its further investigation by others (notably
A. Kekule and A. S. Couper), led to the introduction of the word
equivalent into chemical terminology in a new sense, and in particular
to an understanding of the affinities or "valency" of different
elements, which proved of the most fundamental importance. Thus it
was shown that, of the four elements that enter most prominently into
organic compounds, hydrogen can link itself with only a single bond to
any other element--it has, so to speak, but a single hand with which
to grasp--while oxygen has capacity for two bonds, nitrogen for
three (possibly for five), and carbon for four. The words monovalent,
divalent, trivalent, tretrava-lent, etc., were coined to express this
most important fact, and the various elements came to be known as
monads, diads, triads, etc. Just why different elements should differ
thus in valency no one as yet knows; it is an empirical fact that they
do. And once the nature of any element has been determined as regards
its valency, a most important insight into the possible behavior of that
element has been secured. Thus a consideration of the fact that hydrogen
is monovalent, while oxygen is divalent, makes it plain that we
must expect to find no more than three compounds of these two
elements--namely, H--O--(written HO by the chemist, and called
hydroxyl); H--O--H (H2O, or water), and H--O--O--H (H2O2, or hydrogen
peroxide). It will be observed that in the first of these compounds the
atom of oxygen stands, so to speak, with one of its hands free, eagerly
reaching out, therefore, for another companion, and hence, in the
language of chemistry, forming an unstable compound. Again, in the third
compound, though all hands are clasped, yet one pair links oxygen with
oxygen; and this also must be an unstable union, since the avidity of an
atom for its own kind is relatively weak. Thus the well-known properties
of hydrogen peroxide are explained, its easy decomposition, and the
eagerness with which it seizes upon the elements of other compounds.

But the molecule of water, on the other hand, has its atoms arranged
in a state of stable equilibrium, all their affinities being satisfied.
Each hydrogen atom has satisfied its own affinity by clutching the
oxygen atom; and the oxygen atom has both its bonds satisfied by
clutching back at the two hydrogen atoms. Therefore the trio, linked in
this close bond, have no tendency to reach out for any other companion,
nor, indeed, any power to hold another should it thrust itself
upon them. They form a "stable" compound, which under all ordinary
circumstances will retain its identity as a molecule of water, even
though the physical mass of which it is a part changes its condition
from a solid to a gas from ice to vapor.

But a consideration of this condition of stable equilibrium in the
molecule at once suggests a new question: How can an aggregation of
atoms, having all their affinities satisfied, take any further part in
chemical reactions? Seemingly such a molecule, whatever its physical
properties, must be chemically inert, incapable of any atomic
readjustments. And so in point of fact it is, so long as its component
atoms cling to one another unremittingly. But this, it appears, is
precisely what the atoms are little prone to do. It seems that they are
fickle to the last degree in their individual attachments, and are as
prone to break away from bondage as they are to enter into it. Thus the
oxygen atom which has just flung itself into the circuit of two
hydrogen atoms, the next moment flings itself free again and seeks
new companions. It is for all the world like the incessant change
of partners in a rollicking dance. This incessant dissolution and
reformation of molecules in a substance which as a whole remains
apparently unchanged was first fully appreciated by Ste.-Claire Deville,
and by him named dissociation. It is a process which goes on much more
actively in some compounds than in others, and very much more actively
under some physical conditions (such as increase of temperature) than
under others. But apparently no substances at ordinary temperatures,
and no temperature above the absolute zero, are absolutely free from its
disturbing influence. Hence it is that molecules having all the
valency of their atoms fully satisfied do not lose their chemical
activity--since each atom is momentarily free in the exchange of
partners, and may seize upon different atoms from its former partners,
if those it prefers are at hand.

While, however, an appreciation of this ceaseless activity of the atom
is essential to a proper understanding of its chemical efficiency,
yet from another point of view the "saturated" molecule--that is, the
molecule whose atoms have their valency all satisfied--may be thought of
as a relatively fixed or stable organism. Even though it may presently
be torn down, it is for the time being a completed structure; and a
consideration of the valency of its atoms gives the best clew that has
hitherto been obtainable as to the character of its architecture.
How important this matter of architecture of the molecule--of space
relations of the atoms--may be--was demonstrated as long ago as 1823,
when Liebig and Wohler proved, to the utter bewilderment of the
chemical world, that two substances may have precisely the same chemical
constitution--the same number and kind of atoms--and yet differ utterly
in physical properties. The word isomerism was coined by Berzelius to
express this anomalous condition of things, which seemed to negative the
most fundamental truths of chemistry. Naming the condition by no means
explained it, but the fact was made clear that something besides the
mere number and kind of atoms is important in the architecture of a
molecule. It became certain that atoms are not thrown together haphazard
to build a molecule, any more than bricks are thrown together at random
to form a house.

How delicate may be the gradations of architectural design in building
a molecule was well illustrated about 1850, when Pasteur discovered that
some carbon compounds--as certain sugars--can only be distinguished
from one another, when in solution, by the fact of their twisting or
polarizing a ray of light to the left or to the right, respectively. But
no inkling of an explanation of these strange variations of molecular
structure came until the discovery of the law of valency. Then much of
the mystery was cleared away; for it was plain that since each atom in a
molecule can hold to itself only a fixed number of other atoms, complex
molecules must have their atoms linked in definite chains or groups. And
it is equally plain that where the atoms are numerous, the exact plan of
grouping may sometimes be susceptible of change without doing violence
to the law of valency. It is in such cases that isomerism is observed to

By paying constant heed to this matter of the affinities, chemists are
able to make diagrammatic pictures of the plan of architecture of any
molecule whose composition is known. In the simple molecule of water
(H2O), for example, the two hydrogen atoms must have released each
other before they could join the oxygen, and the manner of linking must
apparently be that represented in the graphic formula H--O--H.
With molecules composed of a large number of atoms, such graphic
representation of the scheme of linking is of course increasingly
difficult, yet, with the affinities for a guide, it is always possible.
Of course no one supposes that such a formula, written in a single
plane, can possibly represent the true architecture of the molecule:
it is at best suggestive or diagrammatic rather than pictorial.
Nevertheless, it affords hints as to the structure of the molecule such
as the fathers of chemistry would not have thought it possible ever to


These utterly novel studies of molecular architecture may seem at
first sight to take from the atom much of its former prestige as the
all-important personage of the chemical world. Since so much depends
upon the mere position of the atoms, it may appear that comparatively
little depends upon the nature of the atoms themselves. But such a view
is incorrect, for on closer consideration it will appear that at no
time has the atom been seen to renounce its peculiar personality. Within
certain limits the character of a molecule may be altered by changing
the positions of its atoms (just as different buildings may be
constructed of the same bricks), but these limits are sharply defined,
and it would be as impossible to exceed them as it would be to build
a stone building with bricks. From first to last the brick remains a
brick, whatever the style of architecture it helps to construct; it
never becomes a stone. And just as closely does each atom retain its own
peculiar properties, regardless of its surroundings.

Thus, for example, the carbon atom may take part in the formation at one
time of a diamond, again of a piece of coal, and yet again of a
particle of sugar, of wood fibre, of animal tissue, or of a gas in the
atmosphere; but from first to last--from glass-cutting gem to intangible
gas--there is no demonstrable change whatever in any single property of
the atom itself. So far as we know, its size, its weight, its capacity
for vibration or rotation, and its inherent affinities, remain
absolutely unchanged throughout all these varying fortunes of position
and association. And the same thing is true of every atom of all of
the seventy-odd elementary substances with which the modern chemist is
acquainted. Every one appears always to maintain its unique integrity,
gaining nothing and losing nothing.

All this being true, it would seem as if the position of the Daltonian
atom as a primordial bit of matter, indestructible and non-transmutable,
had been put to the test by the chemistry of our century, and not found
wanting. Since those early days of the century when the electric battery
performed its miracles and seemingly reached its limitations in the
hands of Davy, many new elementary substances have been discovered,
but no single element has been displaced from its position as an
undecomposable body. Rather have the analyses of the chemist seemed to
make it more and more certain that all elementary atoms are in truth
what John Herschel called them, "manufactured articles"--primordial,
changeless, indestructible.

And yet, oddly enough, it has chanced that hand in hand with the
experiments leading to such a goal have gone other experiments arid
speculations of exactly the opposite tenor. In each generation there
have been chemists among the leaders of their science who have refused
to admit that the so-called elements are really elements at all in any
final sense, and who have sought eagerly for proof which might warrant
their scepticism. The first bit of evidence tending to support this view
was furnished by an English physician, Dr. William Prout, who in 1815
called attention to a curious relation to be observed between the atomic
weight of the various elements. Accepting the figures given by the
authorities of the time (notably Thomson and Berzelius), it appeared
that a strikingly large proportion of the atomic weights were exact
multiples of the weight of hydrogen, and that others differed so
slightly that errors of observation might explain the discrepancy. Prout
felt that it could not be accidental, and he could think of no tenable
explanation, unless it be that the atoms of the various alleged elements
are made up of different fixed numbers of hydrogen atoms. Could it be
that the one true element--the one primal matter--is hydrogen, and that
all other forms of matter are but compounds of this original substance?

Prout advanced this startling idea at first tentatively, in an anonymous
publication; but afterwards he espoused it openly and urged its
tenability. Coming just after Davy's dissociation of some supposed
elements, the idea proved alluring, and for a time gained such
popularity that chemists were disposed to round out the observed atomic
weights of all elements into whole numbers. But presently renewed
determinations of the atomic weights seemed to discountenance this
practice, and Prout's alleged law fell into disrepute. It was revived,
however, about 1840, by Dumas, whose great authority secured it a
respectful hearing, and whose careful redetermination of the weight
of carbon, making it exactly twelve times that of hydrogen, aided the

Subsequently Stas, the pupil of Dumas, undertook a long series of
determinations of atomic weights, with the expectation of confirming the
Proutian hypothesis. But his results seemed to disprove the hypothesis,
for the atomic weights of many elements differed from whole numbers by
more, it was thought, than the limits of error of the experiments. It
was noteworthy, however, that the confidence of Dumas was not shaken,
though he was led to modify the hypothesis, and, in accordance with
previous suggestions of Clark and of Marignac, to recognize as the
primordial element, not hydrogen itself, but an atom half the weight,
or even one-fourth the weight, of that of hydrogen, of which primordial
atom the hydrogen atom itself is compounded. But even in this modified
form the hypothesis found great opposition from experimental observers.

In 1864, however, a novel relation between the weights of the elements
and their other characteristics was called to the attention of chemists
by Professor John A. R. Newlands, of London, who had noticed that if the
elements are arranged serially in the numerical order of their atomic
weights, there is a curious recurrence of similar properties at
intervals of eight elements This so-called "law of octaves" attracted
little immediate attention, but the facts it connotes soon came under
the observation of other chemists, notably of Professors Gustav Hinrichs
in America, Dmitri Mendeleeff in Russia, and Lothar Meyer in Germany.
Mendeleeff gave the discovery fullest expression, explicating it in
1869, under the title of "the periodic law."

Though this early exposition of what has since been admitted to be a
most important discovery was very fully outlined, the generality of
chemists gave it little heed till a decade or so later, when three new
elements, gallium, scandium, and germanium, were discovered, which, on
being analyzed, were quite unexpectedly found to fit into three gaps
which Mendeleeff had left in his periodic scale. In effect the periodic
law had enabled Mendeleeff to predicate the existence of the new
elements years before they were discovered. Surely a system that leads
to such results is no mere vagary. So very soon the periodic law took
its place as one of the most important generalizations of chemical

This law of periodicity was put forward as an expression of observed
relations independent of hypothesis; but of course the theoretical
bearings of these facts could not be overlooked. As Professor J. H.
Gladstone has said, it forces upon us "the conviction that the elements
are not separate bodies created without reference to one another, but
that they have been originally fashioned, or have been built up, from
one another, according to some general plan." It is but a short step
from that proposition to the Proutian hypothesis.


But the atomic weights are not alone in suggesting the compound nature
of the alleged elements. Evidence of a totally different kind has
contributed to the same end, from a source that could hardly have been
imagined when the Proutian hypothesis, was formulated, through the
tradition of a novel weapon to the armamentarium of the chemist--the
spectroscope. The perfection of this instrument, in the hands of two
German scientists, Gustav Robert Kirchhoff and Robert Wilhelm Bunsen,
came about through the investigation, towards the middle of the century,
of the meaning of the dark lines which had been observed in the solar
spectrum by Fraunhofer as early as 1815, and by Wollaston a decade
earlier. It was suspected by Stokes and by Fox Talbot in England, but
first brought to demonstration by Kirchhoff and Bunsen, that these
lines, which were known to occupy definite positions in the spectrum,
are really indicative of particular elementary substances. By means of
the spectroscope, which is essentially a magnifying lens attached to a
prism of glass, it is possible to locate the lines with great accuracy,
and it was soon shown that here was a new means of chemical analysis
of the most exquisite delicacy. It was found, for example, that the
spectroscope could detect the presence of a quantity of sodium so
infinitesimal as the one two-hundred-thousandth of a grain. But what was
even more important, the spectroscope put no limit upon the distance of
location of the substance it tested, provided only that sufficient light
came from it. The experiments it recorded might be performed in the sun,
or in the most distant stars or nebulae; indeed, one of the earliest
feats of the instrument was to wrench from the sun the secret of his
chemical constitution.

To render the utility of the spectroscope complete, however, it
was necessary to link with it another new chemical agency--namely,
photography. This now familiar process is based on the property of light
to decompose certain unstable compounds of silver, and thus alter their
chemical composition. Davy and Wedgwood barely escaped the discovery of
the value of the photographic method early in the nineteenth century.
Their successors quite overlooked it until about 1826, when Louis J. M.
Daguerre, the French chemist, took the matter in hand, and after many
years of experimentation brought it to relative perfection in 1839, in
which year the famous daguerreotype first brought the matter to popular
attention. In the same year Mr. Fox Talbot read a paper on the subject
before the Royal Society, and soon afterwards the efforts of Herschel
and numerous other natural philosophers contributed to the advancement
of the new method.

In 1843 Dr. John W. Draper, the famous English-American chemist and
physiologist, showed that by photography the Fraunhofer lines in the
solar spectrum might be mapped with absolute accuracy; also proving that
the silvered film revealed many lines invisible to the unaided eye. The
value of this method of observation was recognized at once, and, as
soon as the spectroscope was perfected, the photographic method, in
conjunction with its use, became invaluable to the chemist. By this
means comparisons of spectra may be made with a degree of accuracy
not otherwise obtainable; and, in case of the stars, whole clusters of
spectra may be placed on record at a single observation.

As the examination of the sun and stars proceeded, chemists were amazed
or delighted, according to their various preconceptions, to witness the
proof that many familiar terrestrial elements are to be found in the
celestial bodies. But what perhaps surprised them most was to observe
the enormous preponderance in the sidereal bodies of the element
hydrogen. Not only are there vast quantities of this element in the
sun's atmosphere, but some other suns appeared to show hydrogen lines
almost exclusively in their spectra. Presently it appeared that the
stars of which this is true are those white stars, such as Sirius, which
had been conjectured to be the hottest; whereas stars that are only
red-hot, like our sun, show also the vapors of many other elements,
including iron and other metals.

In 1878 Professor J. Norman Lockyer, in a paper before the Royal
Society, called attention to the possible significance of this series of
observations. He urged that the fact of the sun showing fewer elements
than are observed here on the cool earth, while stars much hotter than
the sun show chiefly one element, and that one hydrogen, the lightest of
known elements, seemed to give color to the possibility that our alleged
elements are really compounds, which at the temperature of the hottest
stars may be decomposed into hydrogen, the latter "element" itself being
also doubtless a compound, which might be resolved under yet more trying

Here, then, was what might be termed direct experimental evidence for
the hypothesis of Prout. Unfortunately, however, it is evidence of a
kind which only a few experts are competent to discuss--so very delicate
a matter is the spectral analysis of the stars. What is still more
unfortunate, the experts do not agree among themselves as to the
validity of Professor Lockyer's conclusions. Some, like Professor
Crookes, have accepted them with acclaim, hailing Lockyer as "the
Darwin of the inorganic world," while others have sought a different
explanation of the facts he brings forward. As yet it cannot be said
that the controversy has been brought to final settlement. Still, it is
hardly to be doubted that now, since the periodic law has seemed to
join hands with the spectroscope, a belief in the compound nature of the
so-called elements is rapidly gaining ground among chemists. More and
more general becomes the belief that the Daltonian atom is really a
compound radical, and that back of the seeming diversity of the alleged
elements is a single form of primordial matter. Indeed, in very recent
months, direct experimental evidence for this view has at last come to
hand, through the study of radio-active substances. In a later chapter
we shall have occasion to inquire how this came about.



An epoch in physiology was made in the eighteenth century by the genius
and efforts of Albrecht von Haller (1708-1777), of Berne, who is perhaps
as worthy of the title "The Great" as any philosopher who has been
so christened by his contemporaries since the time of Hippocrates.
Celebrated as a physician, he was proficient in various fields, being
equally famed in his own time as poet, botanist, and statesman, and
dividing his attention between art and science.

As a child Haller was so sickly that he was unable to amuse himself with
the sports and games common to boys of his age, and so passed most of
his time poring over books. When ten years of age he began writing poems
in Latin and German, and at fifteen entered the University of Tubingen.
At seventeen he wrote learned articles in opposition to certain accepted
doctrines, and at nineteen he received his degree of doctor. Soon after
this he visited England, where his zeal in dissecting brought him under
suspicion of grave-robbery, which suspicion made it expedient for him to
return to the Continent. After studying botany in Basel for some time he
made an extended botanical journey through Switzerland, finally settling
in his native city, Berne, as a practising physician. During this time
he did not neglect either poetry or botany, publishing anonymously a
collection of poems.

In 1736 he was called to Gottingen as professor of anatomy, surgery,
chemistry, and botany. During his labors in the university he never
neglected his literary work, sometimes living and sleeping for days and
nights together in his library, eating his meals while delving in his
books, and sleeping only when actually compelled to do so by fatigue.
During all this time he was in correspondence with savants from all over
the world, and it is said of him that he never left a letter of any kind

Haller's greatest contribution to medical science was his famous
doctrine of irritability, which has given him the name of "father of
modern nervous physiology," just as Harvey is called "the father of
the modern physiology of the blood." It has been said of this
famous doctrine of irritability that "it moved all the minds of the
century--and not in the departments of medicine alone--in a way of which
we of the present day have no satisfactory conception, unless we compare
it with our modern Darwinism."(1)

The principle of general irritability had been laid down by Francis
Glisson (1597-1677) from deductive studies, but Haller proved by
experiments along the line of inductive methods that this irritability
was not common to all "fibre as well as to the fluids of the body," but
something entirely special, and peculiar only to muscular substance. He
distinguished between irritability of muscles and sensibility of nerves.
In 1747 he gave as the three forces that produce muscular movements:
elasticity, or "dead nervous force"; irritability, or "innate nervous
force"; and nervous force in itself. And in 1752 he described one
hundred and ninety experiments for determining what parts of the body
possess "irritability"--that is, the property of contracting when
stimulated. His conclusion that this irritability exists in muscular
substance alone and is quite independent of the nerves proceeding to it
aroused a controversy that was never definitely settled until late in
the nineteenth century, when Haller's theory was found to be entirely

It was in pursuit of experiments to establish his theory of irritability
that Haller made his chief discoveries in embryology and development. He
proved that in the process of incubation of the egg the first trace of
the heart of the chick shows itself in the thirty-eighth hour, and that
the first trace of red blood showed in the forty-first hour. By his
investigations upon the lower animals he attempted to confirm the theory
that since the creation of genus every individual is derived from a
preceding individual--the existing theory of preformation, in which
he believed, and which taught that "every individual is fully and
completely preformed in the germ, simply growing from microscopic to
visible proportions, without developing any new parts."

In physiology, besides his studies of the nervous system, Haller studied
the mechanism of respiration, refuting the teachings of Hamberger
(1697-1755), who maintained that the lungs contract independently.
Haller, however, in common with his contemporaries, failed utterly to
understand the true function of the lungs. The great physiologist's
influence upon practical medicine, while most profound, was largely
indirect. He was a theoretical rather than a practical physician, yet he
is credited with being the first physician to use the watch in counting
the pulse.


A great contemporary of Haller was Giovanni Battista Morgagni
(1682-1771), who pursued what Sydenham had neglected, the investigation
in anatomy, thus supplying a necessary counterpart to the great
Englishman's work. Morgagni's investigations were directed chiefly to
the study of morbid anatomy--the study of the structure of diseased
tissue, both during life and post mortem, in contrast to the normal
anatomical structures. This work cannot be said to have originated
with him; for as early as 1679 Bonnet had made similar, although less
extensive, studies; and later many investigators, such as Lancisi and
Haller, had made post-mortem studies. But Morgagni's De sedibus et
causis morborum per anatomen indagatis was the largest, most accurate,
and best-illustrated collection of cases that had ever been brought
together, and marks an epoch in medical science. From the time of the
publication of Morgagni's researches, morbid anatomy became a recognized
branch of the medical science, and the effect of the impetus thus given
it has been steadily increasing since that time.


William Hunter (1718-1783) must always be remembered as one of the
greatest physicians and anatomists of the eighteenth century, and
particularly as the first great teacher of anatomy in England; but his
fame has been somewhat overshadowed by that of his younger brother John.

Hunter had been intended and educated for the Church, but on the advice
of the surgeon William Cullen he turned his attention to the study of
medicine. His first attempt at teaching was in 1746, when he delivered
a series of lectures on surgery for the Society of Naval Practitioners.
These lectures proved so interesting and instructive that he was at
once invited to give others, and his reputation as a lecturer was soon
established. He was a natural orator and story-teller, and he combined
with these attractive qualities that of thoroughness and clearness in
demonstrations, and although his lectures were two hours long he made
them so full of interest that his pupils seldom tired of listening.
He believed that he could do greater good to the world by "publicly
teaching his art than by practising it," and even during the last few
days of his life, when he was so weak that his friends remonstrated
against it, he continued his teaching, fainting from exhaustion at the
end of his last lecture, which preceded his death by only a few days.

For many years it was Hunter's ambition to establish a museum where the
study of anatomy, surgery, and medicine might be advanced, and in 1765
he asked for a grant of a plot of ground for this purpose, offering to
spend seven thousand pounds on its erection besides endowing it with a
professorship of anatomy. Not being able to obtain this grant, however,
he built a house, in which were lecture and dissecting rooms, and his
museum. In this museum were anatomical preparations, coins, minerals,
and natural-history specimens.

Hunter's weakness was his love of controversy and his resentment of
contradiction. This brought him into strained relations with many of
the leading physicians of his time, notably his own brother John, who
himself was probably not entirely free from blame in the matter. Hunter
is said to have excused his own irritability on the grounds that being
an anatomist, and accustomed to "the passive submission of dead bodies,"
contradictions became the more unbearable. Many of the physiological
researches begun by him were carried on and perfected by his more famous
brother, particularly his investigations of the capillaries, but he
added much to the anatomical knowledge of several structures of the
body, notably as to the structure of cartilages and joints.


In Abbot Islip's chapel in Westminster Abbey, close to the resting-place
of Ben Jonson, rest the remains of John Hunter (1728-1793), famous in
the annals of medicine as among the greatest physiologists and surgeons
that the world has ever produced: a man whose discoveries and inventions
are counted by scores, and whose field of research was only limited by
the outermost boundaries of eighteenth-century science, although his
efforts were directed chiefly along the lines of his profession.

Until about twenty years of age young Hunter had shown little aptitude
for study, being unusually fond of out-door sports and amusements; but
about that time, realizing that some occupation must be selected, he
asked permission of his brother William to attempt some dissections in
his anatomical school in London. To the surprise of his brother he made
this dissection unusually well; and being given a second, he acquitted
himself with such skill that his brother at once predicted that he would
become a great anatomist. Up to this time he had had no training of
any kind to prepare him for his professional career, and knew little of
Greek or Latin--languages entirely unnecessary for him, as he proved
in all of his life work. Ottley tells the story that, when twitted with
this lack of knowledge of the "dead languages" in after life, he said
of his opponent, "I could teach him that on the dead body which he never
knew in any language, dead or living."

By his second year in dissection he had become so skilful that he was
given charge of some of the classes in his brother's school; in 1754 he
became a surgeon's pupil in St. George's Hospital, and two years later
house-surgeon. Having by overwork brought on symptoms that seemed to
threaten consumption, he accepted the position of staff-surgeon to an
expedition to Belleisle in 1760, and two years later was serving with
the English army at Portugal. During all this time he was constantly
engaged in scientific researches, many of which, such as his
observations of gun-shot wounds, he put to excellent use in later life.
On returning to England much improved in health in 1763, he entered at
once upon his career as a London surgeon, and from that time forward
his progress was a practically uninterrupted series of successes in his

Hunter's work on the study of the lymphatics was of great service to
the medical profession. This important net-work of minute vessels
distributed throughout the body had recently been made the object of
much study, and various students, including Haller, had made extensive
investigations since their discovery by Asellius. But Hunter, in 1758,
was the first to discover the lymphatics in the neck of birds, although
it was his brother William who advanced the theory that the function
of these vessels was that of absorbents. One of John Hunter's pupils,
William Hewson (1739-1774), first gave an account, in 1768, of
the lymphatics in reptiles and fishes, and added to his teacher's
investigations of the lymphatics in birds. These studies of the
lymphatics have been regarded, perhaps with justice, as Hunter's most
valuable contributions to practical medicine.

In 1767 he met with an accident by which he suffered a rupture of
the tendo Achillis--the large tendon that forms the attachment of the
muscles of the calf to the heel. From observations of this accident,
and subsequent experiments upon dogs, he laid the foundation for the
now simple and effective operation for the cure of club feet and other
deformities involving the tendons. In 1772 he moved into his residence
at Earlscourt, Brompton, where he gathered about him a great menagerie
of animals, birds, reptiles, insects, and fishes, which he used in his
physiological and surgical experiments. Here he performed a countless
number of experiments--more, probably, than "any man engaged in
professional practice has ever conducted." These experiments varied
in nature from observations of the habits of bees and wasps to major
surgical operations performed upon hedgehogs, dogs, leopards, etc. It
is said that for fifteen years he kept a flock of geese for the sole
purpose of studying the process of development in eggs.

Hunter began his first course of lectures in 1772, being forced to do
this because he had been so repeatedly misquoted, and because he felt
that he could better gauge his own knowledge in this way. Lecturing was
a sore trial to him, as he was extremely diffident, and without writing
out his lectures in advance he was scarcely able to speak at all. In
this he presented a marked contrast to his brother William, who was
a fluent and brilliant speaker. Hunter's lectures were at best simple
readings of the facts as he had written them, the diffident teacher
seldom raising his eyes from his manuscript and rarely stopping
until his complete lecture had been read through. His lectures were,
therefore, instructive rather than interesting, as he used infinite care
in preparing them; but appearing before his classes was so dreaded by
him that he is said to have been in the habit of taking a half-drachm of
laudanum before each lecture to nerve him for the ordeal. One is led to
wonder by what name he shall designate that quality of mind that renders
a bold and fearless surgeon like Hunter, who is undaunted in the face
of hazardous and dangerous operations, a stumbling, halting, and
"frightened" speaker before a little band of, at most, thirty young
medical students. And yet this same thing is not unfrequently seen among
the boldest surgeons.

Hunter's Operation for the Cure of Aneurisms

It should be an object-lesson to those who, ignorantly or otherwise,
preach against the painless vivisection as practised to-day, that by the
sacrifice of a single deer in the cause of science Hunter discovered a
fact in physiology that has been the means of saving thousands of human
lives and thousands of human bodies from needless mutilation. We refer
to the discovery of the "collateral circulation" of the blood,
which led, among other things, to Hunter's successful operation upon

Simply stated, every organ or muscle of the body is supplied by one
large artery, whose main trunk distributes the blood into its lesser
branches, and thence through the capillaries. Cutting off this main
artery, it would seem, should cut off entirely the blood-supply to the
particular organ which is supplied by this vessel; and until the time of
Hunter's demonstration this belief was held by most physiologists. But
nature has made a provision for this possible stoppage of blood-supply
from a single source, and has so arranged that some of the small
arterial branches coming from the main supply-trunk are connected with
other arterial branches coming from some other supply-trunk. Under
normal conditions the main arterial trunks supply their respective
organs, the little connecting arterioles playing an insignificant part.
But let the main supply-trunk be cut off or stopped for whatever reason,
and a remarkable thing takes place. The little connecting branches
begin at once to enlarge and draw blood from the neighboring uninjured
supply-trunk, This enlargement continues until at last a new route for
the circulation has been established, the organ no longer depending
on the now defunct original arterial trunk, but getting on as well as
before by this "collateral" circulation that has been established.

The thorough understanding of this collateral circulation is one of the
most important steps in surgery, for until it was discovered amputations
were thought necessary in such cases as those involving the artery
supplying a leg or arm, since it was supposed that, the artery being
stopped, death of the limb and the subsequent necessity for amputation
were sure to follow. Hunter solved this problem by a single operation
upon a deer, and his practicality as a surgeon led him soon after to
apply this knowledge to a certain class of surgical cases in a most
revolutionary and satisfactory manner.

What led to Hunter's far-reaching discovery was his investigation as to
the cause of the growth of the antlers of the deer. Wishing to ascertain
just what part the blood-supply on the opposite sides of the neck played
in the process of development, or, perhaps more correctly, to see what
effect cutting off the main blood-supply would have, Hunter had one of
the deer of Richmond Park caught and tied, while he placed a ligature
around one of the carotid arteries--one of the two principal arteries
that supply the head with blood. He observed that shortly after this the
antler (which was only half grown and consequently very vascular) on the
side of the obliterated artery became cold to the touch--from the lack
of warmth-giving blood. There was nothing unexpected in this, and Hunter
thought nothing of it until a few days later, when he found, to his
surprise, that the antler had become as warm as its fellow, and was
apparently increasing in size. Puzzled as to how this could be, and
suspecting that in some way his ligature around the artery had not been
effective, he ordered the deer killed, and on examination was astonished
to find that while his ligature had completely shut off the blood-supply
from the source of that carotid artery, the smaller arteries had become
enlarged so as to supply the antler with blood as well as ever, only by
a different route.

Hunter soon had a chance to make a practical application of the
knowledge thus acquired. This was a case of popliteal aneurism,
operations for which had heretofore proved pretty uniformly fatal. An
aneurism, as is generally understood, is an enlargement of a certain
part of an artery, this enlargement sometimes becoming of enormous size,
full of palpitating blood, and likely to rupture with fatal results at
any time. If by any means the blood can be allowed to remain quiet for
even a few hours in this aneurism it will form a clot, contract, and
finally be absorbed and disappear without any evil results. The problem
of keeping the blood quiet, with the heart continually driving it
through the vessel, is not a simple one, and in Hunter's time was
considered so insurmountable that some surgeons advocated amputation
of any member having an aneurism, while others cut down upon the tumor
itself and attempted to tie off the artery above and below. The first
of these operations maimed the patient for life, while the second was
likely to prove fatal.

In pondering over what he had learned about collateral circulation and
the time required for it to become fully established, Hunter conceived
the idea that if the blood-supply was cut off from above the aneurism,
thus temporarily preventing the ceaseless pulsations from the heart,
this blood would coagulate and form a clot before the collateral
circulation could become established or could affect it. The patient
upon whom he performed his now celebrated operation was afflicted with
a popliteal aneurism--that is, the aneurism was located on the large
popliteal artery just behind the knee-joint. Hunter, therefore, tied off
the femoral, or main supplying artery in the thigh, a little distance
above the aneurism. The operation was entirely successful, and in six
weeks' time the patient was able to leave the hospital, and with two
sound limbs. Naturally the simplicity and success of this operation
aroused the attention of Europe, and, alone, would have made the name of
Hunter immortal in the annals of surgery. The operation has ever since
been called the "Hunterian" operation for aneurism, but there is reason
to believe that Dominique Anel (born about 1679) performed a somewhat
similar operation several years earlier. It is probable, however, that
Hunter had never heard of this work of Anel, and that his operation
was the outcome of his own independent reasoning from the facts he had
learned about collateral circulation. Furthermore, Hunter's mode of
operation was a much better one than Anel's, and, while Anel's must
claim priority, the credit of making it widely known will always be

The great services of Hunter were recognized both at home and abroad,
and honors and positions of honor and responsibility were given him. In
1776 he was appointed surgeon-extraordinary to the king; in 1783 he
was elected a member of the Royal Society of Medicine and of the Royal
Academy of Surgery at Paris; in 1786 he became deputy surgeon-general
of the army; and in 1790 he was appointed surgeon-general and
inspector-general of hospitals. All these positions he filled with
credit, and he was actively engaged in his tireless pursuit of knowledge
and in discharging his many duties when in October, 1793, he was
stricken while addressing some colleagues, and fell dead in the arms of
a fellow-physician.


Hunter's great rival among contemporary physiologists was the Italian
Lazzaro Spallanzani (1729-1799), one of the most picturesque figures
in the history of science. He was not educated either as a scientist or
physician, devoting, himself at first to philosophy and the languages,
afterwards studying law, and later taking orders. But he was a keen
observer of nature and of a questioning and investigating mind, so that
he is remembered now chiefly for his discoveries and investigations
in the biological sciences. One important demonstration was his
controversion of the theory of abiogenesis, or "spontaneous generation,"
as propounded by Needham and Buffon. At the time of Needham's
experiments it had long been observed that when animal or vegetable
matter had lain in water for a little time--long enough for it to begin
to undergo decomposition--the water became filled with microscopic
creatures, the "infusoria animalculis." This would tend to show, either
that the water or the animal or vegetable substance contained the
"germs" of these minute organisms, or else that they were generated
spontaneously. It was known that boiling killed these animalcules,
and Needham agreed, therefore, that if he first heated the meat or
vegetables, and also the water containing them, and then placed them in
hermetically scaled jars--if he did this, and still the animalcules
made their appearance, it would be proof-positive that they had been
generated spontaneously. Accordingly he made numerous experiments,
always with the same results--that after a few days the water was found
to swarm with the microscopic creatures. The thing seemed proven beyond
question--providing, of course, that there had been no slips in the

But Abbe Spallanzani thought that he detected such slips in Needham's
experiment. The possibility of such slips might come in several ways:
the contents of the jar might not have been boiled for a sufficient
length of time to kill all the germs, or the air might not have
been excluded completely by the sealing process. To cover both these
contingencies, Spallanzani first hermetically sealed the glass vessels
and then boiled them for three-quarters of an hour. Under these
circumstances no animalcules ever made their appearance--a conclusive
demonstration that rendered Needham's grounds for his theory at once

Allied to these studies of spontaneous generation were Spallanzani's
experiments and observations on the physiological processes of
generation among higher animals. He experimented with frogs, tortoises,
and dogs; and settled beyond question the function of the ovum and
spermatozoon. Unfortunately he misinterpreted the part played by the
spermatozoa in believing that their surrounding fluid was equally active
in the fertilizing process, and it was not until some forty years later
(1824) that Dumas corrected this error.


Among the most interesting researches of Spallanzani were his
experiments to prove that digestion, as carried on in the stomach, is a
chemical process. In this he demonstrated, as Rene Reaumur had attempted
to demonstrate, that digestion could be carried on outside the walls of
the stomach as an ordinary chemical reaction, using the gastric juice
as the reagent for performing the experiment. The question as to whether
the stomach acted as a grinding or triturating organ, rather than as a
receptacle for chemical action, had been settled by Reaumur and was
no longer a question of general dispute. Reaumur had demonstrated
conclusively that digestion would take place in the stomach in the same
manner and the same time if the substance to be digested was protected
from the peristalic movements of the stomach and subjected to the action
of the gastric juice only. He did this by introducing the substances to
be digested into the stomach in tubes, and thus protected so that while
the juices of the stomach could act upon them freely they would not be
affected by any movements of the organ.

Following up these experiments, he attempted to show that digestion
could take place outside the body as well as in it, as it certainly
should if it were a purely chemical process. He collected quantities
of gastric juice, and placing it in suitable vessels containing crushed
grain or flesh, kept the mixture at about the temperature of the body
for several hours. After repeated experiments of this kind, apparently
conducted with great care, Reaumur reached the conclusion that "the
gastric juice has no more effect out of the living body in dissolving
or digesting the food than water, mucilage, milk, or any other bland
fluid."(3) Just why all of these experiments failed to demonstrate a
fact so simple does not appear; but to Spallanzani, at least, they
were by no means conclusive, and he proceeded to elaborate upon the
experiments of Reaumur. He made his experiments in scaled tubes exposed
to a certain degree of heat, and showed conclusively that the chemical
process does go on, even when the food and gastric juice are removed
from their natural environment in the stomach. In this he was opposed
by many physiologists, among them John Hunter, but the truth of his
demonstrations could not be shaken, and in later years we find Hunter
himself completing Spallanzani's experiments by his studies of the
post-mortem action of the gastric juice upon the stomach walls.

That Spallanzani's and Hunter's theories of the action of the gastric
juice were not at once universally accepted is shown by an essay written
by a learned physician in 1834. In speaking of some of Spallanzani's
demonstrations, he writes: "In some of the experiments, in order to give
the flesh or grains steeped in the gastric juice the same temperature
with the body, the phials were introduced under the armpits. But this is
not a fair mode of ascertaining the effects of the gastric juice out of
the body; for the influence which life may be supposed to have on the
solution of the food would be secured in this case. The affinities
connected with life would extend to substances in contact with any part
of the system: substances placed under the armpits are not placed at
least in the same circumstances with those unconnected with a living
animal." But just how this writer reaches the conclusion that "the
experiments of Reaumur and Spallanzani give no evidence that the gastric
juice has any peculiar influence more than water or any other bland
fluid in digesting the food"(4) is difficult to understand.

The concluding touches were given to the new theory of digestion by
John Hunter, who, as we have seen, at first opposed Spallanzani, but
who finally became an ardent champion of the chemical theory. Hunter now
carried Spallanzani's experiments further and proved the action of the
digestive fluids after death. For many years anatomists had been puzzled
by pathological lesion of the stomach, found post mortem, when no
symptoms of any disorder of the stomach had been evinced during life.
Hunter rightly conceived that these lesions were caused by the action
of the gastric juice, which, while unable to act upon the living tissue,
continued its action chemically after death, thus digesting the walls
of the stomach in which it had been formed. And, as usual with his
observations, he turned this discovery to practical use in accounting
for certain phenomena of digestion. The following account of the stomach
being digested after death was written by Hunter at the desire of
Sir John Pringle, when he was president of the Royal Society, and the
circumstance which led to this is as follows: "I was opening, in his
presence, the body of a patient of his own, where the stomach was in
part dissolved, which appeared to him very unaccountable, as there had
been no previous symptom that could have led him to suspect any
disease in the stomach. I took that opportunity of giving him my ideas
respecting it, and told him that I had long been making experiments
on digestion, and considered this as one of the facts which proved a
converting power in the gastric juice.... There are a great many powers
in nature which the living principle does not enable the animal matter,
with which it is combined, to resist--viz., the mechanical and most
of the strongest chemical solvents. It renders it, however, capable of
resisting the powers of fermentation, digestion, and perhaps several
others, which are well known to act on the same matter when deprived of
the living principle and entirely to decompose it."

Hunter concludes his paper with the following paragraph: "These
appearances throw considerable light on the principle of digestion,
and show that it is neither a mechanical power, nor contractions of the
stomach, nor heat, but something secreted in the coats of the stomach,
and thrown into its cavity, which there animalizes the food or
assimilates it to the nature of the blood. The power of this juice is
confined or limited to certain substances, especially of the vegetable
and animal kingdoms; and although this menstruum is capable of acting
independently of the stomach, yet it is indebted to that viscus for its


It is a curious commentary on the crude notions of mechanics of previous
generations that it should have been necessary to prove by experiment
that the thin, almost membranous stomach of a mammal has not the power
to pulverize, by mere attrition, the foods that are taken into it.
However, the proof was now for the first time forthcoming, and the
question of the general character of the function of digestion was
forever set at rest. Almost simultaneously with this great advance,
corresponding progress was made in an allied field: the mysteries of
respiration were at last cleared up, thanks to the new knowledge of
chemistry. The solution of the problem followed almost as a matter
of course upon the advances of that science in the latter part of the
century. Hitherto no one since Mayow, of the previous century, whose
flash of insight had been strangely overlooked and forgotten, had even
vaguely surmised the true function of the lungs. The great Boerhaave
had supposed that respiration is chiefly important as an aid to the
circulation of the blood; his great pupil, Haller, had believed to the
day of his death in 1777 that the main purpose of the function is to
form the voice. No genius could hope to fathom the mystery of the lungs
so long as air was supposed to be a simple element, serving a mere
mechanical purpose in the economy of the earth.

But the discovery of oxygen gave the clew, and very soon all the
chemists were testing the air that came from the lungs--Dr. Priestley,
as usual, being in the van. His initial experiments were made in
1777, and from the outset the problem was as good as solved. Other
experimenters confirmed his results in all their essentials--notably
Scheele and Lavoisier and Spallanzani and Davy. It was clearly
established that there is chemical action in the contact of the air with
the tissue of the lungs; that some of the oxygen of the air disappears,
and that carbonic-acid gas is added to the inspired air. It was shown,
too, that the blood, having come in contact with the air, is changed
from black to red in color. These essentials were not in dispute from
the first. But as to just what chemical changes caused these results
was the subject of controversy. Whether, for example, oxygen is actually
absorbed into the blood, or whether it merely unites with carbon given
off from the blood, was long in dispute.

Each of the main disputants was biased by his own particular views as
to the moot points of chemistry. Lavoisier, for example, believed oxygen
gas to be composed of a metal oxygen combined with the alleged element
heat; Dr. Priestley thought it a compound of positive electricity and
phlogiston; and Humphry Davy, when he entered the lists a little later,
supposed it to be a compound of oxygen and light. Such mistaken notions
naturally complicated matters and delayed a complete understanding of
the chemical processes of respiration. It was some time, too, before the
idea gained acceptance that the most important chemical changes do not
occur in the lungs themselves, but in the ultimate tissues. Indeed,
the matter was not clearly settled at the close of the century.
Nevertheless, the problem of respiration had been solved in its
essentials. Moreover, the vastly important fact had been established
that a process essentially identical with respiration is necessary to
the existence not only of all creatures supplied with lungs, but to
fishes, insects, and even vegetables--in short, to every kind of living


Some interesting experiments regarding vegetable respiration were made
just at the close of the century by Erasmus Darwin, and recorded in his
Botanic Garden as a foot-note to the verse:

"While spread in air the leaves respiring play."

These notes are worth quoting at some length, as they give a clear idea
of the physiological doctrines of the time (1799), while taking advance
ground as to the specific matter in question:

"There have been various opinions," Darwin says, "concerning the use of
the leaves of plants in the vegetable economy. Some have contended
that they are perspiratory organs. This does not seem probable from an
experiment of Dr. Hales, Vegetable Statics, p. 30. He, found, by cutting
off branches of trees with apples on them and taking off the leaves,
that an apple exhaled about as much as two leaves the surfaces of which
were nearly equal to the apple; whence it would appear that apples have
as good a claim to be termed perspiratory organs as leaves. Others have
believed them excretory organs of excrementitious juices, but as
the vapor exhaled from vegetables has no taste, this idea is no more
probable than the other; add to this that in most weathers they do not
appear to perspire or exhale at all.

"The internal surface of the lungs or air-vessels in men is said to
be equal to the external surface of the whole body, or almost fifteen
square feet; on this surface the blood is exposed to the influence of
the respired air through the medium, however, of a thin pellicle; by
this exposure to the air it has its color changed from deep red to
bright scarlet, and acquires something so necessary to the existence of
life that we can live scarcely a minute without this wonderful process.

"The analogy between the leaves of plants and the lungs or gills of
animals seems to embrace so many circumstances that we can scarcely
withhold our consent to their performing similar offices.

"1. The great surface of leaves compared to that of the trunk and
branches of trees is such that it would seem to be an organ well adapted
for the purpose of exposing the vegetable juices to the influence of the
air; this, however, we shall see afterwards is probably performed only
by their upper surfaces, yet even in this case the surface of the leaves
in general bear a greater proportion to the surface of the tree than the
lungs of animals to their external surfaces.

"2. In the lung of animals the blood, after having been exposed to the
air in the extremities of the pulmonary artery, is changed in color
from deep red to bright scarlet, and certainly in some of its essential
properties it is then collected by the pulmonary vein and returned
to the heart. To show a similarity of circumstances in the leaves of
plants, the following experiment was made, June 24, 1781. A stalk with
leaves and seed-vessels of large spurge (Euphorbia helioscopia) had been
several days placed in a decoction of madder (Rubia tinctorum) so that
the lower part of the stem and two of the undermost leaves were immersed
in it. After having washed the immersed leaves in clear water I could
readily discover the color of the madder passing along the middle rib
of each leaf. The red artery was beautifully visible on the under and on
the upper surface of the leaf; but on the upper side many red branches
were seen going from it to the extremities of the leaf, which on the
other side were not visible except by looking through it against the
light. On this under side a system of branching vessels carrying a
pale milky fluid were seen coming from the extremities of the leaf, and
covering the whole under side of it, and joining two large veins, one
on each side of the red artery in the middle rib of the leaf, and along
with it descending to the foot-stalk or petiole. On slitting one of
these leaves with scissors, and having a magnifying-glass ready, the
milky blood was seen oozing out of the returning veins on each side of
the red artery in the middle rib, but none of the red fluid from the

"All these appearances were more easily seen in a leaf of Picris treated
in the same manner; for in this milky plant the stems and middle rib of
the leaves are sometimes naturally colored reddish, and hence the color
of the madder seemed to pass farther into the ramifications of their
leaf-arteries, and was there beautifully visible with the returning
branches of milky veins on each side."

Darwin now goes on to draw an incorrect inference from his observations:

"3. From these experiments," he says, "the upper surface of the leaf
appeared to be the immediate organ of respiration, because the colored
fluid was carried to the extremities of the leaf by vessels most
conspicuous on the upper surface, and there changed into a milky fluid,
which is the blood of the plant, and then returned by concomitant
veins on the under surface, which were seen to ooze when divided with
scissors, and which, in Picris, particularly, render the under surface
of the leaves greatly whiter than the upper one."

But in point of fact, as studies of a later generation were to show, it
is the under surface of the leaf that is most abundantly provided
with stomata, or "breathing-pores." From the stand-point of this later
knowledge, it is of interest to follow our author a little farther,
to illustrate yet more fully the possibility of combining correct
observations with a faulty inference.

"4. As the upper surface of leaves constitutes the organ of respiration,
on which the sap is exposed in the termination of arteries beneath a
thin pellicle to the action of the atmosphere, these surfaces in many
plants strongly repel moisture, as cabbage leaves, whence the particles
of rain lying over their surfaces without touching them, as observed by
Mr. Melville (Essays Literary and Philosophical: Edinburgh), have the
appearance of globules of quicksilver. And hence leaves with the upper
surfaces on water wither as soon as in the dry air, but continue green
for many days if placed with the under surface on water, as appears
in the experiments of Monsieur Bonnet (Usage des Feuilles). Hence some
aquatic plants, as the water-lily (Nymphoea), have the lower sides
floating on the water, while the upper surfaces remain dry in the air.

"5. As those insects which have many spiracula, or breathing apertures,
as wasps and flies, are immediately suffocated by pouring oil upon them,
I carefully covered with oil the surfaces of several leaves of phlomis,
of Portugal laurel, and balsams, and though it would not regularly
adhere, I found them all die in a day or two.

"It must be added that many leaves are furnished with muscles about
their foot-stalks, to turn their surfaces to the air or light, as mimosa
or Hedysarum gyrans. From all these analogies I think there can be no
doubt but that leaves of trees are their lungs, giving out a phlogistic
material to the atmosphere, and absorbing oxygen, or vital air.

"6. The great use of light to vegetation would appear from this theory
to be by disengaging vital air from the water which they perspire, and
thence to facilitate its union with their blood exposed beneath the
thin surface of their leaves; since when pure air is thus applied it
is probable that it can be more readily absorbed. Hence, in the curious
experiments of Dr. Priestley and Mr. Ingenhouz, some plants purified
less air than others--that is, they perspired less in the sunshine;
and Mr. Scheele found that by putting peas into water which about
half covered them they converted the vital air into fixed air, or
carbonic-acid gas, in the same manner as in animal respiration.

"7. The circulation in the lungs or leaves of plants is very similar
to that of fish. In fish the blood, after having passed through their
gills, does not return to the heart as from the lungs of air-breathing
animals, but the pulmonary vein taking the structure of an artery after
having received the blood from the gills, which there gains a more
florid color, distributes it to the other parts of their bodies. The
same structure occurs in the livers of fish, whence we see in those
animals two circulations independent of the power of the heart--viz.,
that beginning at the termination of the veins of the gills and
branching through the muscles, and that which passes through the liver;
both which are carried on by the action of those respective arteries and

Darwin is here a trifle fanciful in forcing the analogy between plants
and animals. The circulatory system of plants is really not quite
so elaborately comparable to that of fishes as he supposed. But the
all-important idea of the uniformity underlying the seeming diversity
of Nature is here exemplified, as elsewhere in the writings of Erasmus
Darwin; and, more specifically, a clear grasp of the essentials of the
function of respiration is fully demonstrated.


Several causes conspired to make exploration all the fashion during the
closing epoch of the eighteenth century. New aid to the navigator
had been furnished by the perfected compass and quadrant, and by the
invention of the chronometer; medical science had banished scurvy, which
hitherto had been a perpetual menace to the voyager; and, above all, the
restless spirit of the age impelled the venturesome to seek novelty in
fields altogether new. Some started for the pole, others tried for a
northeast or northwest passage to India, yet others sought the great
fictitious antarctic continent told of by tradition. All these of course
failed of their immediate purpose, but they added much to the world's
store of knowledge and its fund of travellers' tales.

Among all these tales none was more remarkable than those which told of
strange living creatures found in antipodal lands. And here, as did not
happen in every field, the narratives were often substantiated by the
exhibition of specimens that admitted no question. Many a company of
explorers returned more or less laden with such trophies from the
animal and vegetable kingdoms, to the mingled astonishment, delight, and
bewilderment of the closet naturalists. The followers of Linnaeus in the
"golden age of natural history," a few decades before, had increased the
number of known species of fishes to about four hundred, of birds to one
thousand, of insects to three thousand, and of plants to ten thousand.
But now these sudden accessions from new territories doubled the figure
for plants, tripled it for fish and birds, and brought the number of
described insects above twenty thousand. Naturally enough, this wealth
of new material was sorely puzzling to the classifiers. The more
discerning began to see that the artificial system of Linnaeus,
wonderful and useful as it had been, must be advanced upon before the
new material could be satisfactorily disposed of. The way to a more
natural system, based on less arbitrary signs, had been pointed out by
Jussieu in botany, but the zoologists were not prepared to make headway
towards such a system until they should gain a wider understanding of
the organisms with which they had to deal through comprehensive studies
of anatomy. Such studies of individual forms in their relations to the
entire scale of organic beings were pursued in these last decades of
the century, but though two or three most important generalizations were
achieved (notably Kaspar Wolff's conception of the cell as the basis of
organic life, and Goethe's all-important doctrine of metamorphosis of
parts), yet, as a whole, the work of the anatomists of the period was
germinative rather than fruit-bearing. Bichat's volumes, telling of the
recognition of the fundamental tissues of the body, did not begin to
appear till the last year of the century. The announcement by Cuvier of
the doctrine of correlation of parts bears the same date, but in general
the studies of this great naturalist, which in due time were to stamp
him as the successor of Linnaeus, were as yet only fairly begun.



We have seen that the focal points of the physiological world towards
the close of the eighteenth century were Italy and England, but when
Spallanzani and Hunter passed away the scene shifted to France. The
time was peculiarly propitious, as the recent advances in many lines of
science had brought fresh data for the student of animal life which were
in need of classification, and, as several minds capable of such a task
were in the field, it was natural that great generalizations should have
come to be quite the fashion. Thus it was that Cuvier came forward with
a brand-new classification of the animal kingdom, establishing
four great types of being, which he called vertebrates, mollusks,
articulates, and radiates. Lamarck had shortly before established the
broad distinction between animals with and those without a backbone;
Cuvier's Classification divided the latter--the invertebrates--into
three minor groups. And this division, familiar ever since to all
students of zoology, has only in very recent years been supplanted, and
then not by revolution, but by a further division, which the elaborate
recent studies of lower forms of life seemed to make desirable.

In the course of those studies of comparative anatomy which led to his
new classification, Cuvier's attention was called constantly to the
peculiar co-ordination of parts in each individual organism. Thus an
animal with sharp talons for catching living prey--as a member of the
cat tribe--has also sharp teeth, adapted for tearing up the flesh of its
victim, and a particular type of stomach, quite different from that of
herbivorous creatures. This adaptation of all the parts of the animal
to one another extends to the most diverse parts of the organism, and
enables the skilled anatomist, from the observation of a single typical
part, to draw inferences as to the structure of the entire animal--a
fact which was of vast aid to Cuvier in his studies of paleontology. It
did not enable Cuvier, nor does it enable any one else, to reconstruct
fully the extinct animal from observation of a single bone, as has
sometimes been asserted, but what it really does establish, in the hands
of an expert, is sufficiently astonishing.

"While the study of the fossil remains of the greater quadrupeds is more
satisfactory," he writes, "by the clear results which it affords, than
that of the remains of other animals found in a fossil state, it is also
complicated with greater and more numerous difficulties. Fossil shells
are usually found quite entire, and retaining all the characters
requisite for comparing them with the specimens contained in collections
of natural history, or represented in the works of naturalists. Even the
skeletons of fishes are found more or less entire, so that the general
forms of their bodies can, for the most part, be ascertained,
and usually, at least, their generic and specific characters are
determinable, as these are mostly drawn from their solid parts. In
quadrupeds, on the contrary, even when their entire skeletons are
found, there is great difficulty in discovering their distinguishing
characters, as these are chiefly founded upon their hairs and colors and
other marks which have disappeared previous to their incrustation. It is
also very rare to find any fossil skeletons of quadrupeds in any degree
approaching to a complete state, as the strata for the most part only
contain separate bones, scattered confusedly and almost always broken
and reduced to fragments, which are the only means left to naturalists
for ascertaining the species or genera to which they have belonged.

"Fortunately comparative anatomy, when thoroughly understood, enables
us to surmount all these difficulties, as a careful application of its
principles instructs us in the correspondences and dissimilarities of
the forms of organized bodies of different kinds, by which each may be
rigorously ascertained from almost every fragment of its various parts
and organs.

"Every organized individual forms an entire system of its own, all the
parts of which naturally correspond, and concur to produce a certain
definite purpose, by reciprocal reaction, or by combining towards the
same end. Hence none of these separate parts can change their forms
without a corresponding change in the other parts of the same animal,
and consequently each of these parts, taken separately, indicates all
the other parts to which it has belonged. Thus, as I have elsewhere
shown, if the viscera of an animal are so organized as only to be fitted
for the digestion of recent flesh, it is also requisite that the jaws
should be so constructed as to fit them for devouring prey; the claws
must be constructed for seizing and tearing it to pieces; the teeth
for cutting and dividing its flesh; the entire system of the limbs,
or organs of motion, for pursuing and overtaking it; and the organs of
sense for discovering it at a distance. Nature must also have endowed
the brain of the animal with instincts sufficient for concealing itself
and for laying plans to catch its necessary victims....

"To enable the animal to carry off its prey when seized, a corresponding
force is requisite in the muscles which elevate the head, and this
necessarily gives rise to a determinate form of the vertebrae to which
these muscles are attached and of the occiput into which they are
inserted. In order that the teeth of a carnivorous animal may be able to
cut the flesh, they require to be sharp, more or less so in proportion
to the greater or less quantity of flesh that they have to cut. It is
requisite that their roots should be solid and strong, in proportion to
the quantity and size of the bones which they have to break to pieces.
The whole of these circumstances must necessarily influence the
development and form of all the parts which contribute to move the

After these observations, it will be easily seen that similar
conclusions may be drawn with respect to the limbs of carnivorous
animals, which require particular conformations to fit them for rapidity
of motion in general; and that similar considerations must influence the
forms and connections of the vertebrae and other bones constituting the
trunk of the body, to fit them for flexibility and readiness of motion
in all directions. The bones also of the nose, of the orbit, and of
the ears require certain forms and structures to fit them for giving
perfection to the senses of smell, sight, and hearing, so necessary to
animals of prey. In short, the shape and structure of the teeth regulate
the forms of the condyle, of the shoulder-blade, and of the claws,
in the same manner as the equation of a curve regulates all its other
properties; and as in regard to any particular curve all its properties
may be ascertained by assuming each separate property as the foundation
of a particular equation, in the same manner a claw, a shoulder-blade,
a condyle, a leg or arm bone, or any other bone separately considered,
enables us to discover the description of teeth to which they have
belonged; and so also reciprocally we may determine the forms of the
other bones from the teeth. Thus commencing our investigations by a
careful survey of any one bone by itself, a person who is sufficiently
master of the laws of organic structure may, as it were, reconstruct the
whole animal to which that bone belonged."(1)

We have already pointed out that no one is quite able to perform the
necromantic feat suggested in the last sentence; but the exaggeration is
pardonable in the enthusiast to whom the principle meant so much and in
whose hands it extended so far.

Of course this entire principle, in its broad outlines, is something
with which every student of anatomy had been familiar from the time
when anatomy was first studied, but the full expression of the "law
of co-ordination," as Cuvier called it, had never been explicitly made
before; and, notwithstanding its seeming obviousness, the exposition
which Cuvier made of it in the introduction to his classical work on
comparative anatomy, which was published during the first decade of
the nineteenth century, ranks as a great discovery. It is one of those
generalizations which serve as guideposts to other discoveries.


Much the same thing may be said of another generalization regarding the
animal body, which the brilliant young French physician Marie Francois
Bichat made in calling attention to the fact that each vertebrate
organism, including man, has really two quite different sets of
organs--one set under volitional control, and serving the end of
locomotion, the other removed from volitional control, and serving the
ends of the "vital processes" of digestion, assimilation, and the like.
He called these sets of organs the animal system and the organic system,
respectively. The division thus pointed out was not quite new, for
Grimaud, professor of physiology in the University of Montpellier,
had earlier made what was substantially the same classification of the
functions into "internal or digestive and external or locomotive"; but
it was Bichat's exposition that gave currency to the idea.

Far more important, however, was another classification which Bichat put
forward in his work on anatomy, published just at the beginning of the
last century. This was the division of all animal structures into what
Bichat called tissues, and the pointing out that there are really only
a few kinds of these in the body, making up all the diverse organs. Thus
muscular organs form one system; membranous organs another; glandular
organs a third; the vascular mechanism a fourth, and so on. The
distinction is so obvious that it seems rather difficult to conceive
that it could have been overlooked by the earliest anatomists; but, in
point of fact, it is only obvious because now it has been familiarly
taught for almost a century. It had never been given explicit expression
before the time of Bichat, though it is said that Bichat himself was
somewhat indebted for it to his master, Desault, and to the famous
alienist Pinel.

However that may be, it is certain that all subsequent anatomists have
found Bichat's classification of the tissues of the utmost value in
their studies of the animal functions. Subsequent advances were to
show that the distinction between the various tissues is not really
so fundamental as Bichat supposed, but that takes nothing from the
practical value of the famous classification.

It was but a step from this scientific classification of tissues to a
similar classification of the diseases affecting them, and this was one
of the greatest steps towards placing medicine on the plane of an exact
science. This subject of these branches completely fascinated Bichat,
and he exclaimed, enthusiastically: "Take away some fevers and nervous
trouble, and all else belongs to the kingdom of pathological anatomy."
But out of this enthusiasm came great results. Bichat practised as he
preached, and, believing that it was only possible to understand disease
by observing the symptoms carefully at the bedside, and, if the disease
terminated fatally, by post-mortem examination, he was so arduous in his
pursuit of knowledge that within a period of less than six months he had
made over six hundred autopsies--a record that has seldom, if ever,
been equalled. Nor were his efforts fruitless, as a single example will
suffice to show. By his examinations he was able to prove that diseases
of the chest, which had formerly been classed under the indefinite name
"peripneumonia," might involve three different structures, the pleural
sac covering the lungs, the lung itself, and the bronchial tubes, the
diseases affecting these organs being known respectively as pleuritis,
pneumonia, and bronchitis, each one differing from the others as to
prognosis and treatment. The advantage of such an exact classification
needs no demonstration.


At the same time when these broad macroscopical distinctions were being
drawn there were other workers who were striving to go even deeper into
the intricacies of the animal mechanism with the aid of the microscope.
This undertaking, however, was beset with very great optical
difficulties, and for a long time little advance was made upon the work
of preceding generations. Two great optical barriers, known technically
as spherical and chromatic aberration--the one due to a failure of the
rays of light to fall all in one plane when focalized through a lens,
the other due to the dispersive action of the lens in breaking the
white light into prismatic colors--confronted the makers of microscopic
lenses, and seemed all but insuperable. The making of achromatic lenses
for telescopes had been accomplished, it is true, by Dolland in the
previous century, by the union of lenses of crown glass with those of
flint glass, these two materials having different indices of refraction
and dispersion. But, aside from the mechanical difficulties which arise
when the lens is of the minute dimensions required for use with the
microscope, other perplexities are introduced by the fact that the use
of a wide pencil of light is a desideratum, in order to gain sufficient
illumination when large magnification is to be secured.

In the attempt to overcome those difficulties, the foremost physical
philosophers of the time came to the aid of the best opticians. Very
early in the century, Dr. (afterwards Sir David) Brewster, the renowned
Scotch physicist, suggested that certain advantages might accrue from
the use of such gems as have high refractive and low dispersive indices,
in place of lenses made of glass. Accordingly lenses were made of
diamond, of sapphire, and so on, and with some measure of success. But
in 1812 a much more important innovation was introduced by Dr. William
Hyde Wollaston, one of the greatest and most versatile, and, since
the death of Cavendish, by far the most eccentric of English natural
philosophers. This was the suggestion to use two plano-convex
lenses, placed at a prescribed distance apart, in lieu of the single
double-convex lens generally used. This combination largely overcame
the spherical aberration, and it gained immediate fame as the "Wollaston

To obviate loss of light in such a doublet from increase of reflecting
surfaces, Dr. Brewster suggested filling the interspace between the two
lenses with a cement having the same index of refraction as the lenses
themselves--an improvement of manifest advantage. An improvement yet
more important was made by Dr. Wollaston himself in the introduction of
the diaphragm to limit the field of vision between the lenses, instead
of in front of the anterior lens. A pair of lenses thus equipped Dr.
Wollaston called the periscopic microscope. Dr. Brewster suggested that
in such a lens the same object might be attained with greater ease by
grinding an equatorial groove about a thick or globular lens and filling
the groove with an opaque cement. This arrangement found much favor,
and came subsequently to be known as a Coddington lens, though Mr.
Coddington laid no claim to being its inventor.

Sir John Herschel, another of the very great physicists of the time,
also gave attention to the problem of improving the microscope, and in
1821 he introduced what was called an aplanatic combination of lenses,
in which, as the name implies, the spherical aberration was largely
done away with. It was thought that the use of this Herschel aplanatic
combination as an eyepiece, combined with the Wollaston doublet for the
objective, came as near perfection as the compound microscope was likely
soon to come. But in reality the instrument thus constructed, though
doubtless superior to any predecessor, was so defective that for
practical purposes the simple microscope, such as the doublet or the
Coddington, was preferable to the more complicated one.

Many opticians, indeed, quite despaired of ever being able to make a
satisfactory refracting compound microscope, and some of them had taken
up anew Sir Isaac Newton's suggestion in reference to a reflecting
microscope. In particular, Professor Giovanni Battista Amici, a very
famous mathematician and practical optician of Modena, succeeded in
constructing a reflecting microscope which was said to be superior to
any compound microscope of the time, though the events of the ensuing
years were destined to rob it of all but historical value. For there
were others, fortunately, who did not despair of the possibilities of
the refracting microscope, and their efforts were destined before
long to be crowned with a degree of success not even dreamed of by any
preceding generation.

The man to whom chief credit is due for directing those final steps
that made the compound microscope a practical implement instead of a
scientific toy was the English amateur optician Joseph Jackson Lister.
Combining mathematical knowledge with mechanical ingenuity, and having
the practical aid of the celebrated optician Tulley, he devised formulae
for the combination of lenses of crown glass with others of flint
glass, so adjusted that the refractive errors of one were corrected
or compensated by the other, with the result of producing lenses of
hitherto unequalled powers of definition; lenses capable of showing an
image highly magnified, yet relatively free from those distortions
and fringes of color that had heretofore been so disastrous to true
interpretation of magnified structures.

Lister had begun his studies of the lens in 1824, but it was not until
1830 that he contributed to the Royal Society the famous paper detailing
his theories and experiments. Soon after this various continental
opticians who had long been working along similar lines took the matter
up, and their expositions, in particular that of Amici, introduced
the improved compound microscope to the attention of microscopists
everywhere. And it required but the most casual trial to convince the
experienced observers that a new implement of scientific research had
been placed in their hands which carried them a long step nearer
the observation of the intimate physical processes which lie at the
foundation of vital phenomena. For the physiologist this perfection of
the compound microscope had the same significance that the, discovery
of America had for the fifteenth-century geographers--it promised a
veritable world of utterly novel revelations. Nor was the fulfilment of
that promise long delayed.

Indeed, so numerous and so important were the discoveries now made in
the realm of minute anatomy that the rise of histology to the rank of an
independent science may be said to date from this period. Hitherto, ever
since the discovery of magnifying-glasses, there had been here and there
a man, such as Leuwenhoek or Malpighi, gifted with exceptional vision,
and perhaps unusually happy in his conjectures, who made important
contributions to the knowledge of the minute structure of organic
tissues; but now of a sudden it became possible for the veriest tyro to
confirm or refute the laborious observations of these pioneers, while
the skilled observer could step easily beyond the barriers of vision
that hitherto were quite impassable. And so, naturally enough, the
physiologists of the fourth decade of the nineteenth century rushed
as eagerly into the new realm of the microscope as, for example, their
successors of to-day are exploring the realm of the X-ray.

Lister himself, who had become an eager interrogator of the instrument
he had perfected, made many important discoveries, the most notable
being his final settlement of the long-mooted question as to the true
form of the red corpuscles of the human blood. In reality, as everybody
knows nowadays, these are biconcave disks, but owing to their peculiar
figure it is easily possible to misinterpret the appearances they
present when seen through a poor lens, and though Dr. Thomas Young and
various other observers had come very near the truth regarding them,
unanimity of opinion was possible only after the verdict of the
perfected microscope was given.

These blood corpuscles are so infinitesimal in size that something like
five millions of them are found in each cubic millimetre of the blood,
yet they are isolated particles, each having, so to speak, its own
personality. This, of course, had been known to microscopists since the
days of the earliest lenses. It had been noticed, too, by here and
there an observer, that certain of the solid tissues seemed to present
something of a granular texture, as if they, too, in their ultimate
constitution, were made up of particles. And now, as better and better
lenses were constructed, this idea gained ground constantly, though
for a time no one saw its full significance. In the case of vegetable
tissues, indeed, the fact that little particles encased a membranous
covering, and called cells, are the ultimate visible units of structure
had long been known. But it was supposed that animal tissues differed
radically from this construction. The elementary particles of vegetables
"were regarded to a certain extent as individuals which composed the
entire plant, while, on the other hand, no such view was taken of the
elementary parts of animals."


In the year 1833 a further insight into the nature of the ultimate
particles of plants was gained through the observation of the English
microscopist Robert Brown, who, in the course of his microscopic studies
of the epidermis of orchids, discovered in the cells "an opaque spot,"
which he named the nucleus. Doubtless the same "spot" had been seen
often enough before by other observers, but Brown was the first to
recognize it as a component part of the vegetable cell and to give it a

"I shall conclude my observations on Orchideae," said Brown, "with a
notice of some points of their general structure, which chiefly relate
to the cellular tissue. In each cell of the epidermis of a great part
of this family, especially of those with membranous leaves, a single
circular areola, generally somewhat more opaque than, the membrane of
the cell, is observable. This areola, which is more or less distinctly
granular, is slightly convex, and although it seems to be on the surface
is in reality covered by the outer lamina of the cell. There is no
regularity as to its place in the cell; it is not unfrequently, however,
central or nearly so.

"As only one areola belongs to each cell, and as in many cases where it
exists in the common cells of the epidermis, it is also visible in the
cutaneous glands or stomata, and in these is always double--one being on
each side of the limb--it is highly probable that the cutaneous gland is
in all cases composed of two cells of peculiar form, the line of union
being the longitudinal axis of the disk or pore.

"This areola, or nucleus of the cell as perhaps it might be termed,
is not confined to the epidermis, being also found, not only in the
pubescence of the surface, particularly when jointed, as in cypripedium,
but in many cases in the parenchyma or internal cells of the tissue,
especially when these are free from the deposition of granular matter.

"In the compressed cells of the epidermis the nucleus is in a
corresponding degree flattened; but in the internal tissue it is often
nearly spherical, more or less firmly adhering to one of the walls,
and projecting into the cavity of the cell. In this state it may not
unfrequently be found in the substance of the column and in that of the

"The nucleus is manifest also in the tissue of the stigma, where in
accordance with the compression of the utriculi, it has an intermediate
form, being neither so much flattened as in the epidermis nor so convex
as it is in the internal tissue of the column.

"I may here remark that I am acquainted with one case of apparent
exception to the nucleus being solitary in each utriculus or
cell--namely, in Bletia Tankervilliae. In the utriculi of the stigma of
this plant, I have generally, though not always, found a second areola
apparently on the surface, and composed of much larger granules than the
ordinary nucleus, which is formed of very minute granular matter, and
seems to be deep seated.

"Mr. Bauer has represented the tissue of the stigma, in the species of
Bletia, both before and, as he believes, after impregnation; and in the
latter state the utriculi are marked with from one to three areolae of
similar appearance.

"The nucleus may even be supposed to exist in the pollen of this family.
In the early stages of its formation, at least a minute areola is of
ten visible in the simple grain, and in each of the constituent parts
of cells of the compound grain. But these areolae may perhaps rather be
considered as merely the points of production of the tubes.

"This nucleus of the cell is not confined to orchideae, but is equally
manifest in many other monocotyledonous families; and I have even
found it, hitherto however in very few cases, in the epidermis of
dicotyledonous plants; though in this primary division it may perhaps
be said to exist in the early stages of development of the pollen. Among
monocotyledons, the orders in which it is most remarkable are Liliaceae,
Hemerocallideae, Asphodeleae, Irideae, and Commelineae.

"In some plants belonging to this last-mentioned family, especially
in Tradascantia virginica, and several nearly related species, it is
uncommonly distinct, not in the epidermis and in the jointed hairs of
the filaments, but in the tissue of the stigma, in the cells of the
ovulum even before impregnation, and in all the stages of formation
of the grains of pollen, the evolution of which is so remarkable in

"The few indications of the presence of this nucleus, or areola, that I
have hitherto met with in the publications of botanists are chiefly in
some figures of epidermis, in the recent works of Meyen and Purkinje,
and in one case, in M. Adolphe Broigniart's memoir on the structure of
leaves. But so little importance seems to be attached to it that the
appearance is not always referred to in the explanations of the figures
in which it is represented. Mr. Bauer, however, who has also figured
it in the utriculi of the stigma of Bletia Tankervilliae has more
particularly noticed it, and seems to consider it as only visible after


That this newly recognized structure must be important in the economy of
the cell was recognized by Brown himself, and by the celebrated German
Meyen, who dealt with it in his work on vegetable physiology, published
not long afterwards; but it remained for another German, the professor
of botany in the University of Jena, Dr. M. J. Schleiden, to bring the
nucleus to popular attention, and to assert its all-importance in the
economy of the cell.

Schleiden freely acknowledged his indebtedness to Brown for first
knowledge of the nucleus, but he soon carried his studies of that
structure far beyond those of its discoverer. He came to believe that
the nucleus is really the most important portion of the cell, in that
it is the original structure from which the remainder of the cell is
developed. Hence he named it the cytoblast. He outlined his views in
an epochal paper published in Muller's Archives in 1838, under title of
"Beitrage zur Phytogenesis." This paper is in itself of value, yet the
most important outgrowth of Schleiden's observations of the nucleus did
not spring from his own labors, but from those of a friend to whom he
mentioned his discoveries the year previous to their publication.
This friend was Dr. Theodor Schwann, professor of physiology in the
University of Louvain.

At the moment when these observations were communicated to him Schwann
was puzzling over certain details of animal histology which he could
not clearly explain. His great teacher, Johannes Muller, had called
attention to the strange resemblance to vegetable cells shown by certain
cells of the chorda dorsalis (the embryonic cord from which the spinal
column is developed), and Schwann himself had discovered a corresponding
similarity in the branchial cartilage of a tadpole. Then, too, the
researches of Friedrich Henle had shown that the particles that make up
the epidermis of animals are very cell-like in appearance. Indeed, the
cell-like character of certain animal tissues had come to be matter of
common note among students of minute anatomy. Schwann felt that this
similarity could not be mere coincidence, but he had gained no clew to
further insight until Schleiden called his attention to the nucleus.
Then at once he reasoned that if there really is the correspondence
between vegetable and animal tissues that he suspected, and if the
nucleus is so important in the vegetable cell as Schleiden believed,
the nucleus should also be found in the ultimate particles of animal

Schwann's researches soon showed the entire correctness of this
assumption. A closer study of animal tissues under the microscope
showed, particularly in the case of embryonic tissues, that "opaque
spots" such as Schleiden described are really to be found there
in abundance--forming, indeed, a most characteristic phase of the
structure. The location of these nuclei at comparatively regular
intervals suggested that they are found in definite compartments of the
tissue, as Schleiden had shown to be the case with vegetables; indeed,
the walls that separated such cell-like compartments one from another
were in some cases visible. Particularly was this found to be the case
with embryonic tissues, and the study of these soon convinced Schwann
that his original surmise had been correct, and that all animal tissues
are in their incipiency composed of particles not unlike the ultimate
particles of vegetables in short, of what the botanists termed cells.
Adopting this name, Schwann propounded what soon became famous as his
cell theory, under title of Mikroskopische Untersuchungen uber die
Ubereinstimmung in der Structur und dent Wachsthum der Thiere und
Pflanzen. So expeditious had been his work that this book was published
early in 1839, only a few months after the appearance of Schleiden's

As the title suggests, the main idea that actuated Schwann was to unify
vegetable and animal tissues. Accepting cell-structure as the basis of
all vegetable tissues, he sought to show that the same is true of animal
tissues, all the seeming diversities of fibre being but the alteration
and development of what were originally simple cells. And by cell
Schwann meant, as did Schleiden also, what the word ordinarily
implies--a cavity walled in on all sides. He conceived that the ultimate
constituents of all tissues were really such minute cavities, the most
important part of which was the cell wall, with its associated nucleus.
He knew, indeed, that the cell might be filled with fluid contents, but
he regarded these as relatively subordinate in importance to the wall
itself. This, however, did not apply to the nucleus, which was supposed
to lie against the cell wall and in the beginning to generate it.
Subsequently the wall might grow so rapidly as to dissociate itself
from its contents, thus becoming a hollow bubble or true cell; but the
nucleus, as long as it lasted, was supposed to continue in contact
with the cell wall. Schleiden had even supposed the nucleus to be a
constituent part of the wall, sometimes lying enclosed between two
layers of its substance, and Schwann quoted this view with seeming
approval. Schwann believed, however, that in the mature cell the nucleus
ceased to be functional and disappeared.

The main thesis as to the similarity of development of vegetable and
animal tissues and the cellular nature of the ultimate constitution
of both was supported by a mass of carefully gathered evidence which a
multitude of microscopists at once confirmed, so Schwann's work became
a classic almost from the moment of its publication. Of course various
other workers at once disputed Schwann's claim to priority of discovery,
in particular the English microscopist Valentin, who asserted, not
without some show of justice, that he was working closely along the same
lines. Put so, for that matter, were numerous others, as Henle, Turpin,
Du-mortier, Purkinje, and Muller, all of whom Schwann himself had
quoted. Moreover, there were various physiologists who earlier than
any of these had foreshadowed the cell theory--notably Kaspar Friedrich
Wolff, towards the close of the previous century, and Treviranus about
1807, But, as we have seen in so many other departments of science, it
is one thing to foreshadow a discovery, it is quite another to give
it full expression and make it germinal of other discoveries. And when
Schwann put forward the explicit claim that "there is one universal
principle of development for the elementary parts, of organisms, however
different, and this principle is the formation of cells," he enunciated
a doctrine which was for all practical purposes absolutely new and
opened up a novel field for the microscopist to enter. A most important
era in physiology dates from the publication of his book in 1839.


That Schwann should have gone to embryonic tissues for the establishment
of his ideas was no doubt due very largely to the influence of the great
Russian Karl Ernst von Baer, who about ten years earlier had published
the first part of his celebrated work on embryology, and whose ideas
were rapidly gaining ground, thanks largely to the advocacy of a few
men, notably Johannes Muller, in Germany, and William B. Carpenter, in
England, and to the fact that the improved microscope had made minute
anatomy popular. Schwann's researches made it plain that the best
field for the study of the animal cell is here, and a host of explorers
entered the field. The result of their observations was, in the main,
to confirm the claims of Schwann as to the universal prevalence of the
cell. The long-current idea that animal tissues grow only as a sort
of deposit from the blood-vessels was now discarded, and the fact of
so-called plantlike growth of animal cells, for which Schwann contended,
was universally accepted. Yet the full measure of the affinity between
the two classes of cells was not for some time generally apprehended.

Indeed, since the substance that composes the cell walls of plants is
manifestly very different from the limiting membrane of the animal cell,
it was natural, so long as the wall was considered the most essential
part of the structure, that the divergence between the two classes
of cells should seem very pronounced. And for a time this was the
conception of the matter that was uniformly accepted. But as time
went on many observers had their attention called to the peculiar
characteristics of the contents of the cell, and were led to ask
themselves whether these might not be more important than had been
supposed. In particular, Dr. Hugo von Mohl, professor of botany in the
University of Tubingen, in the course of his exhaustive studies of
the vegetable cell, was impressed with the peculiar and characteristic
appearance of the cell contents. He observed universally within the cell
"an opaque, viscid fluid, having granules intermingled in it," which
made up the main substance of the cell, and which particularly impressed
him because under certain conditions it could be seen to be actively in
motion, its parts separated into filamentous streams.

Von Mohl called attention to the fact that this motion of the cell
contents had been observed as long ago as 1774 by Bonaventura Corti,
and rediscovered in 1807 by Treviranus, and that these observers had
described the phenomenon under the "most unsuitable name of 'rotation
of the cell sap.'" Von Mohl recognized that the streaming substance was
something quite different from sap. He asserted that the nucleus of the
cell lies within this substance and not attached to the cell wall as
Schleiden had contended. He saw, too, that the chlorophyl granules,
and all other of the cell contents, are incorporated with the "opaque,
viscid fluid," and in 1846 he had become so impressed with the
importance of this universal cell substance that he gave it the name
of protoplasm. Yet in so doing he had no intention of subordinating the
cell wall. The fact that Payen, in 1844, had demonstrated that the
cell walls of all vegetables, high or low, are composed largely of one
substance, cellulose, tended to strengthen the position of the cell wall
as the really essential structure, of which the protoplasmic contents
were only subsidiary products.

Meantime, however, the students of animal histology were more and more
impressed with the seeming preponderance of cell contents over cell
walls in the tissues they studied. They, too, found the cell to be
filled with a viscid, slimy fluid capable of motion. To this Dujardin
gave the name of sarcode. Presently it came to be known, through the
labors of Kolliker, Nageli, Bischoff, and various others, that there are
numerous lower forms of animal life which seem to be composed of this
sarcode, without any cell wall whatever. The same thing seemed to be
true of certain cells of higher organisms, as the blood corpuscles.
Particularly in the case of cells that change their shape markedly,
moving about in consequence of the streaming of their sarcode, did it
seem certain that no cell wall is present, or that, if present, its role
must be insignificant.

And so histologists came to question whether, after all, the cell
contents rather than the enclosing wall must not be the really essential
structure, and the weight of increasing observations finally left no
escape from the conclusion that such is really the case. But attention
being thus focalized on the cell contents, it was at once apparent
that there is a far closer similarity between the ultimate particles of
vegetables and those of animals than had been supposed. Cellulose and
animal membrane being now regarded as more by-products, the way was
clear for the recognition of the fact that vegetable protoplasm and
animal sarcode are marvellously similar in appearance and general
properties. The closer the observation the more striking seemed this
similarity; and finally, about 1860, it was demonstrated by Heinrich de
Bary and by Max Schultze that the two are to all intents and purposes
identical. Even earlier Remak had reached a similar conclusion, and
applied Von Mohl's word protoplasm to animal cell contents, and now this
application soon became universal. Thenceforth this protoplasm was
to assume the utmost importance in the physiological world, being
recognized as the universal "physical basis of life," vegetable and
animal alike. This amounted to the logical extension and culmination
of Schwann's doctrine as to the similarity of development of the two
animate kingdoms. Yet at the same time it was in effect the banishment
of the cell that Schwann had defined. The word cell was retained, it
is true, but it no longer signified a minute cavity. It now implied,
as Schultze defined it, "a small mass of protoplasm endowed with the
attributes of life." This definition was destined presently to meet with
yet another modification, as we shall see; but the conception of the
protoplasmic mass as the essential ultimate structure, which might or
might not surround itself with a protective covering, was a permanent
addition to physiological knowledge. The earlier idea had, in effect,
declared the shell the most important part of the egg; this developed
view assigned to the yolk its true position.

In one other important regard the theory of Schleiden and Schwann now
became modified. This referred to the origin of the cell. Schwann had
regarded cell growth as a kind of crystallization, beginning with the
deposit of a nucleus about a granule in the intercellular substance--the
cytoblastema, as Schleiden called it. But Von Mohl, as early as 1835,
had called attention to the formation of new vegetable cells through the
division of a pre-existing cell. Ehrenberg, another high authority of
the time, contended that no such division occurs, and the matter was
still in dispute when Schleiden came forward with his discovery of
so-called free cell-formation within the parent cell, and this for a
long time diverted attention from the process of division which Von Mohl
had described. All manner of schemes of cell-formation were put forward
during the ensuing years by a multitude of observers, and gained
currency notwithstanding Von Mohl's reiterated contention that there
are really but two ways in which the formation of new cells takes
place--namely, "first, through division of older cells; secondly,
through the formation of secondary cells lying free in the cavity of a

But gradually the researches of such accurate observers as Unger,
Nageli, Kolliker, Reichart, and Remak tended to confirm the opinion of
Von Mohl that cells spring only from cells, and finally Rudolf Virchow
brought the matter to demonstration about 1860. His Omnis cellula e
cellula became from that time one of the accepted data of physiology.
This was supplemented a little later by Fleming's Omnis nucleus e
nucleo, when still more refined methods of observation had shown that
the part of the cell which always first undergoes change preparatory to
new cell-formation is the all-essential nucleus. Thus the nucleus was
restored to the important position which Schwann and Schleiden had given
it, but with greatly altered significance. Instead of being a structure
generated de novo from non-cellular substance, and disappearing as soon
as its function of cell-formation was accomplished, the nucleus was now
known as the central and permanent feature of every cell, indestructible
while the cell lives, itself the division-product of a pre-existing
nucleus, and the parent, by division of its substance, of other
generations of nuclei. The word cell received a final definition as "a
small mass of protoplasm supplied with a nucleus."

In this widened and culminating general view of the cell theory it
became clear that every animate organism, animal or vegetable, is but a
cluster of nucleated cells, all of which, in each individual case, are
the direct descendants of a single primordial cell of the ovum. In the
developed individuals of higher organisms the successive generations of
cells become marvellously diversified in form and in specific functions;
there is a wonderful division of labor, special functions being chiefly
relegated to definite groups of cells; but from first to last there is
no function developed that is not present, in a primitive way, in
every cell, however isolated; nor does the developed cell, however
specialized, ever forget altogether any one of its primordial functions
or capacities. All physiology, then, properly interpreted, becomes
merely a study of cellular activities; and the development of the cell
theory takes its place as the great central generalization in physiology
of the nineteenth century. Something of the later developments of this
theory we shall see in another connection.


Just at the time when the microscope was opening up the paths that
were to lead to the wonderful cell theory, another novel line of
interrogation of the living organism was being put forward by a
different set of observers. Two great schools of physiological chemistry
had arisen--one under guidance of Liebig and Wohler, in Germany, the
other dominated by the great French master Jean Baptiste Dumas. Liebig
had at one time contemplated the study of medicine, and Dumas had
achieved distinction in connection with Prevost, at Geneva, in the
field of pure physiology before he turned his attention especially to
chemistry. Both these masters, therefore, and Wohler as well, found
absorbing interest in those phases of chemistry that have to do with the
functions of living tissues; and it was largely through their efforts
and the labors of their followers that the prevalent idea that vital
processes are dominated by unique laws was discarded and physiology was
brought within the recognized province of the chemist. So at about
the time when the microscope had taught that the cell is the really
essential structure of the living organism, the chemists had come to
understand that every function of the organism is really the expression
of a chemical change--that each cell is, in short, a miniature chemical
laboratory. And it was this combined point of view of anatomist and
chemist, this union of hitherto dissociated forces, that made possible
the inroads into the unexplored fields of physiology that were effected
towards the middle of the nineteenth century.

One of the first subjects reinvestigated and brought to proximal
solution was the long-mooted question of the digestion of foods.
Spallanzani and Hunter had shown in the previous century that digestion
is in some sort a solution of foods; but little advance was made upon
their work until 1824, when Prout detected the presence of hydrochloric
acid in the gastric juice. A decade later Sprott and Boyd detected
the existence of peculiar glands in the gastric mucous membrane; and
Cagniard la Tour and Schwann independently discovered that the really
active principle of the gastric juice is a substance which was named
pepsin, and which was shown by Schwann to be active in the presence of
hydrochloric acid.

Almost coincidently, in 1836, it was discovered by Purkinje
and Pappenheim that another organ than the stomach--namely, the
pancreas--has a share in digestion, and in the course of the ensuing
decade it came to be known, through the efforts of Eberle, Valentin,
and Claude Bernard, that this organ is all-important in the digestion
of starchy and fatty foods. It was found, too, that the liver and the
intestinal glands have each an important share in the work of preparing
foods for absorption, as also has the saliva--that, in short, a
coalition of forces is necessary for the digestion of all ordinary foods
taken into the stomach.

And the chemists soon discovered that in each one of the essential
digestive juices there is at least one substance having certain
resemblances to pepsin, though acting on different kinds of food. The
point of resemblance between all these essential digestive agents is
that each has the remarkable property of acting on relatively enormous
quantities of the substance which it can digest without itself being
destroyed or apparently even altered. In virtue of this strange
property, pepsin and the allied substances were spoken of as ferments,
but more recently it is customary to distinguish them from such
organized ferments as yeast by designating them enzymes. The isolation
of these enzymes, and an appreciation of their mode of action, mark a
long step towards the solution of the riddle of digestion, but it must
be added that we are still quite in the dark as to the real ultimate
nature of their strange activity.

In a comprehensive view, the digestive organs, taken as a whole, are
a gateway between the outside world and the more intimate cells of the
organism. Another equally important gateway is furnished by the lungs,
and here also there was much obscurity about the exact method of
functioning at the time of the revival of physiological chemistry. That
oxygen is consumed and carbonic acid given off during respiration the
chemists of the age of Priestley and Lavoisier had indeed made clear,
but the mistaken notion prevailed that it was in the lungs themselves
that the important burning of fuel occurs, of which carbonic acid is a
chief product. But now that attention had been called to the importance
of the ultimate cell, this misconception could not long hold its ground,
and as early as 1842 Liebig, in the course of his studies of animal
heat, became convinced that it is not in the lungs, but in the ultimate
tissues to which they are tributary, that the true consumption of
fuel takes place. Reviving Lavoisier's idea, with modifications and
additions, Liebig contended, and in the face of opposition finally
demonstrated, that the source of animal heat is really the consumption
of the fuel taken in through the stomach and the lungs. He showed that
all the activities of life are really the product of energy liberated
solely through destructive processes, amounting, broadly speaking, to
combustion occurring in the ultimate cells of the organism. Here is his


"The oxygen taken into the system is taken out again in the same forms,
whether in summer or in winter; hence we expire more carbon in cold
weather, and when the barometer is high, than we do in warm weather; and
we must consume more or less carbon in our food in the same proportion;
in Sweden more than in Sicily; and in our more temperate climate a full
eighth more in winter than in summer.

"Even when we consume equal weights of food in cold and warm countries,
infinite wisdom has so arranged that the articles of food in different
climates are most unequal in the proportion of carbon they contain. The
fruits on which the natives of the South prefer to feed do not in the
fresh state contain more than twelve per cent. of carbon, while the
blubber and train-oil used by the inhabitants of the arctic regions
contain from sixty-six to eighty per cent. of carbon.

"It is no difficult matter, in warm climates, to study moderation in
eating, and men can bear hunger for a long time under the equator; but
cold and hunger united very soon exhaust the body.

"The mutual action between the elements of the food and the oxygen
conveyed by the circulation of the blood to every part of the body is
the source of animal heat.

"All living creatures whose existence depends on the absorption of
oxygen possess within themselves a source of heat independent of
surrounding objects.

"This truth applies to all animals, and extends besides to the
germination of seeds, to the flowering of plants, and to the maturation
of fruits. It is only in those parts of the body to which arterial
blood, and with it the oxygen absorbed in respiration, is conveyed that
heat is produced. Hair, wool, or feathers do not possess an elevated
temperature. This high temperature of the animal body, or, as it may be
called, disengagement of heat, is uniformly and under all circumstances
the result of the combination of combustible substance with oxygen.

"In whatever way carbon may combine with oxygen, the act of combination
cannot take place without the disengagement of heat. It is a matter of
indifference whether the combination takes place rapidly or slowly, at a
high or at a low temperature; the amount of heat liberated is a constant
quantity. The carbon of the food, which is converted into carbonic acid
within the body, must give out exactly as much heat as if it had been
directly burned in the air or in oxygen gas; the only difference is that
the amount of heat produced is diffused over unequal times. In oxygen
the combustion is more rapid and the heat more intense; in air it is
slower, the temperature is not so high, but it continues longer.

"It is obvious that the amount of heat liberated must increase or
diminish with the amount of oxygen introduced in equal times by
respiration. Those animals which respire frequently, and consequently
consume much oxygen, possess a higher temperature than others which,
with a body of equal size to be heated, take into the system less
oxygen. The temperature of a child (102 degrees) is higher than that of
an adult (99.5 degrees). That of birds (104 to 105.4 degrees) is higher
than that of quadrupeds (98.5 to 100.4 degrees), or than that of fishes
or amphibia, whose proper temperature is from 3.7 to 2.6 degrees higher
than that of the medium in which they live. All animals, strictly
speaking, are warm-blooded; but in those only which possess lungs is the
temperature of the body independent of the surrounding medium.

"The most trustworthy observations prove that in all climates, in the
temperate zones as well as at the equator or the poles, the temperature
of the body in man, and of what are commonly called warm-blooded
animals, is invariably the same; yet how different are the circumstances
in which they live.

"The animal body is a heated mass, which bears the same relation to
surrounding objects as any other heated mass. It receives heat when the
surrounding objects are hotter, it loses heat when they are colder
than itself. We know that the rapidity of cooling increases with
the difference between the heated body and that of the surrounding
medium--that is, the colder the surrounding medium the shorter the time
required for the cooling of the heated body. How unequal, then, must be
the loss of heat of a man at Palermo, where the actual temperature is
nearly equal to that of the body, and in the polar regions, where the
external temperature is from 70 to 90 degrees lower.

"Yet notwithstanding this extremely unequal loss of heat, experience
has shown that the blood of an inhabitant of the arctic circle has a
temperature as high as that of the native of the South, who lives in so
different a medium. This fact, when its true significance is perceived,
proves that the heat given off to the surrounding medium is restored
within the body with great rapidity. This compensation takes place more
rapidly in winter than in summer, at the pole than at the equator.

"Now in different climates the quantity of oxygen introduced into the
system of respiration, as has been already shown, varies according to
the temperature of the external air; the quantity of inspired oxygen
increases with the loss of heat by external cooling, and the quantity
of carbon or hydrogen necessary to combine with this oxygen must be
increased in like ratio. It is evident that the supply of heat lost by
cooling is effected by the mutual action of the elements of the food and
the inspired oxygen, which combine together. To make use of a familiar,
but not on that account a less just illustration, the animal body acts,
in this respect, as a furnace, which we supply with fuel. It signifies
nothing what intermediate forms food may assume, what changes it may
undergo in the body, the last change is uniformly the conversion
of carbon into carbonic acid and of its hydrogen into water; the
unassimilated nitrogen of the food, along with the unburned or
unoxidized carbon, is expelled in the excretions. In order to keep up
in a furnace a constant temperature, we must vary the supply of fuel
according to the external temperature--that is, according to the supply
of oxygen.

"In the animal body the food is the fuel; with a proper supply of oxygen
we obtain the heat given out during its oxidation or combustion."(3)


Further researches showed that the carriers of oxygen, from the time of
its absorption in the lungs till its liberation in the ultimate tissues,
are the red corpuscles, whose function had been supposed to be the
mechanical one of mixing of the blood. It transpired that the red
corpuscles are composed chiefly of a substance which Kuhne first
isolated in crystalline form in 1865, and which was named haemoglobin--a
substance which has a marvellous affinity for oxygen, seizing on it
eagerly at the lungs vet giving it up with equal readiness when coursing
among the remote cells of the body. When freighted with oxygen it
becomes oxyhaemoglobin and is red in color; when freed from its oxygen
it takes a purple hue; hence the widely different appearance of arterial
and venous blood, which so puzzled the early physiologists.

This proof of the vitally important role played by the red-blood
corpuscles led, naturally, to renewed studies of these infinitesimal
bodies. It was found that they may vary greatly in number at different
periods in the life of the same individual, proving that they may be
both developed and destroyed in the adult organism. Indeed, extended
observations left no reason to doubt that the process of corpuscle
formation and destruction may be a perfectly normal one--that, in
short, every red-blood corpuscle runs its course and dies like any more
elaborate organism. They are formed constantly in the red marrow of
bones, and are destroyed in the liver, where they contribute to the
formation of the coloring matter of the bile. Whether there are other
seats of such manufacture and destruction of the corpuscles is not
yet fully determined. Nor are histologists agreed as to whether the
red-blood corpuscles themselves are to be regarded as true cells, or
merely as fragments of cells budded out from a true cell for a special
purpose; but in either case there is not the slightest doubt that the
chief function of the red corpuscle is to carry oxygen.

If the oxygen is taken to the ultimate cells before combining with
the combustibles it is to consume, it goes without saying that these
combustibles themselves must be carried there also. Nor could it be in
doubt that the chiefest of these ultimate tissues, as regards, quantity
of fuel required, are the muscles. A general and comprehensive view
of the organism includes, then, digestive apparatus and lungs as the
channels of fuel-supply; blood and lymph channels as the transportation
system; and muscle cells, united into muscle fibres, as the consumption
furnaces, where fuel is burned and energy transformed and rendered
available for the purposes of the organism, supplemented by a set of
excretory organs, through which the waste products--the ashes--are
eliminated from the system.

But there remain, broadly speaking, two other sets of organs whose size
demonstrates their importance in the economy of the organism, yet
whose functions are not accounted for in this synopsis. These are those
glandlike organs, such as the spleen, which have no ducts and produce no
visible secretions, and the nervous mechanism, whose central organs are
the brain and spinal cord. What offices do these sets of organs perform
in the great labor-specializing aggregation of cells which we call a
living organism?

As regards the ductless glands, the first clew to their function was
given when the great Frenchman Claude Bernard (the man of whom
his admirers loved to say, "He is not a physiologist merely; he is
physiology itself") discovered what is spoken of as the glycogenic
function of the liver. The liver itself, indeed, is not a ductless
organ, but the quantity of its biliary output seems utterly
disproportionate to its enormous size, particularly when it is
considered that in the case of the human species the liver contains
normally about one-fifth of all the blood in the entire body. Bernard
discovered that the blood undergoes a change of composition in passing
through the liver. The liver cells (the peculiar forms of which had been
described by Purkinje, Henle, and Dutrochet about 1838) have the power
to convert certain of the substances that come to them into a starchlike
compound called glycogen, and to store this substance away till it
is needed by the organism. This capacity of the liver cells is quite
independent of the bile-making power of the same cells; hence the
discovery of this glycogenic function showed that an organ may have
more than one pronounced and important specific function. But its chief
importance was in giving a clew to those intermediate processes between
digestion and final assimilation that are now known to be of such vital
significance in the economy of the organism.

In the forty odd years that have elapsed since this pioneer observation
of Bernard, numerous facts have come to light showing the extreme
importance of such intermediate alterations of food-supplies in the
blood as that performed by the liver. It has been shown that the
pancreas, the spleen, the thyroid gland, the suprarenal capsules
are absolutely essential, each in its own way, to the health of the
organism, through metabolic changes which they alone seem capable of
performing; and it is suspected that various other tissues, including
even the muscles themselves, have somewhat similar metabolic capacities
in addition to their recognized functions. But so extremely intricate is
the chemistry of the substances involved that in no single case has the
exact nature of the metabolisms wrought by these organs been fully made
out. Each is in its way a chemical laboratory indispensable to the
right conduct of the organism, but the precise nature of its operations
remains inscrutable. The vast importance of the operations of these
intermediate organs is unquestioned.

A consideration of the functions of that other set of organs known
collectively as the nervous system is reserved for a later chapter.



When Coleridge said of Humphry Davy that he might have been the greatest
poet of his time had he not chosen rather to be the greatest chemist, it
is possible that the enthusiasm of the friend outweighed the caution of
the critic. But however that may be, it is beyond dispute that the man
who actually was the greatest poet of that time might easily have taken
the very highest rank as a scientist had not the muse distracted his
attention. Indeed, despite these distractions, Johann Wolfgang von
Goethe achieved successes in the field of pure science that would insure
permanent recognition for his name had he never written a stanza of
poetry. Such is the versatility that marks the highest genius.

It was in 1790 that Goethe published the work that laid the foundations
of his scientific reputation--the work on the Metamorphoses of Plants,
in which he advanced the novel doctrine that all parts of the flower are
modified or metamorphosed leaves.

"Every one who observes the growth of plants, even superficially,"
wrote Goethe, "will notice that certain external parts of them become
transformed at times and go over into the forms of the contiguous parts,
now completely, now to a greater or less degree. Thus, for example, the
single flower is transformed into a double one when, instead of stamens,
petals are developed, which are either exactly like the other petals of
the corolla in form, and color or else still bear visible signs of their

"When we observe that it is possible for a plant in this way to take a
step backward, we shall give so much the more heed to the regular course
of nature and learn the laws of transformation according to which she
produces one part through another, and displays the most varying forms
through the modification of one single organ.

"Let us first direct our attention to the plant at the moment when it
develops out of the seed-kernel. The first organs of its upward
growth are known by the name of cotyledons; they have also been called

"They often appear shapeless, filled with new matter, and are just as
thick as they are broad. Their vessels are unrecognizable and are hardly
to be distinguished from the mass of the whole; they bear almost no
resemblance to a leaf, and we could easily be misled into regarding them
as special organs. Occasionally, however, they appear as real leaves,
their vessels are capable of the most minute development, their
similarity to the following leaves does not permit us to take them for
special organs, but we recognize them instead to be the first leaves of
the stalk.

"The cotyledons are mostly double, and there is an observation to be
made here which will appear still more important as we proceed--that
is, that the leaves of the first node are often paired, even when the
following leaves of the stalk stand alternately upon it. Here we see an
approximation and a joining of parts which nature afterwards separates
and places at a distance from one another. It is still more remarkable
when the cotyledons take the form of many little leaves gathered about
an axis, and the stalk which grows gradually from their midst produces
the following leaves arranged around it singly in a whorl. This may be
observed very exactly in the growth of the pinus species. Here a corolla
of needles forms at the same time a calyx, and we shall have occasion to
remember the present case in connection with similar phenomena later.

"On the other hand, we observe that even the cotyledons which are most
like a leaf when compared with the following leaves of the stalk are
always more undeveloped or less developed. This is chiefly noticeable
in their margin which is extremely simple and shows few traces of

"A few or many of the next following leaves are often already present in
the seed, and lie enclosed between the cotyledons; in their folded state
they are known by the name of plumules. Their form, as compared with the
cotyledons and the following leaves, varies in different plants. Their
chief point of variance, however, from the cotyledons is that they are
flat, delicate, and formed like real leaves generally. They are wholly
green, rest on a visible node, and can no longer deny their relationship
to the following leaves of the stalk, to which, however, they are
usually still inferior, in so far as that their margin is not completely

"The further development, however, goes on ceaselessly in the leaf, from
node to node; its midrib is elongated, and more or less additional ribs
stretch out from this towards the sides. The leaves now appear notched,
deeply indented, or composed of several small leaves, in which last case
they seem to form complete little branches. The date-palm furnishes a
striking example of such a successive transformation of the simplest
leaf form. A midrib is elongated through a succession of several
leaves, the single fan-shaped leaf becomes torn and diverted, and a very
complicated leaf is developed, which rivals a branch in form.

"The transition to inflorescence takes place more or less rapidly. In
the latter case we usually observe that the leaves of the stalk loose
their different external divisions, and, on the other hand, spread out
more or less in their lower parts where they are attached to the stalk.
If the transition takes place rapidly, the stalk, suddenly become
thinner and more elongated since the node of the last-developed leaf,
shoots up and collects several leaves around an axis at its end.

"That the petals of the calyx are precisely the same organs which have
hitherto appeared as leaves on the stalk, but now stand grouped about a
common centre in an often very different form, can, as it seems to me,
be most clearly demonstrated. Already in connection with the cotyledons
above, we noticed a similar working of nature. The first species, while
they are developing out of the seed-kernel, display a radiate crown of
unmistakable needles; and in the first childhood of these plants we see
already indicated that force of nature whereby when they are older their
flowering and fruit-giving state will be produced.

"We see this force of nature, which collects several leaves around an
axis, produce a still closer union and make these approximated, modified
leaves still more unrecognizable by joining them together either
wholly or partially. The bell-shaped or so-called one-petalled calices
represent these cloudy connected leaves, which, being more or less
indented from above, or divided, plainly show their origin.

"We can observe the transition from the calyx to the corolla in more
than one instance, for, although the color of the calyx is still usually
green, and like the color of the leaves of the stalk, it nevertheless
often varies in one or another of its parts--at the tips, the margins,
the back, or even, the inward side--while the outer still remains on

"The relationship of the corolla to the leaves of the stalk is shown
in more than one way, since on the stalks of some plants appear leaves
which are already more or less colored long before they approach
inflorescence; others are fully colored when near inflorescence. Nature
also goes over at once to the corolla, sometimes by skipping over the
organs of the calyx, and in such a case we likewise have an opportunity
to observe that leaves of the stalk become transformed into petals. Thus
on the stalk of tulips, for instance, there sometimes appears an almost
completely developed and colored petal. Even more remarkable is the
case when such a leaf, half green and half of it belonging to the stalk,
remains attached to the latter, while another colored part is raised
with the corolla, and the leaf is thus torn in two.

"The relationship between the petals and stamens is very close. In some
instances nature makes the transition regular--e.g., among the Canna
and several plants of the same family. A true, little-modified petal is
drawn together on its upper margin, and produces a pollen sac, while the
rest of the petal takes the place of the stamen. In double flowers
we can observe this transition in all its stages. In several kinds of
roses, within the fully developed and colored petals there appear other
ones which are drawn together in the middle or on the side. This drawing
together is produced by a small weal, which appears as a more or less
complete pollen sac, and in the same proportion the leaf approaches the
simple form of a stamen.

"The pistil in many cases looks almost like a stamen without anthers,
and the relationship between the formation of the two is much closer
than between the other parts. In retrograde fashion nature often
produces cases where the style and stigma (Narben) become retransformed
into petals--that is, the Ranunculus Asiaticus becomes double by
transforming the stigma and style of the fruit-receptacle into real
petals, while the stamens are often found unchanged immediately behind
the corolla.

"In the seed receptacles, in spite of their formation, of their special
object, and of their method of being joined together, we cannot fail to
recognize the leaf form. Thus, for instance, the pod would be a simple
leaf folded and grown together on its margin; the siliqua would consist
of more leaves folded over another; the compound receptacles would be
explained as being several leaves which, being united above one centre,
keep their inward parts separate and are joined on their margins. We can
convince ourselves of this by actual sight when such composite capsules
fall apart after becoming ripe, because then every part displays an
opened pod."(1)

The theory thus elaborated of the metamorphosis of parts was presently
given greater generality through extension to the animal kingdom, in
the doctrine which Goethe and Oken advanced independently, that the
vertebrate skull is essentially a modified and developed vertebra. These
were conceptions worthy of a poet--impossible, indeed, for any mind that
had not the poetic faculty of correlation. But in this case the poet's
vision was prophetic of a future view of the most prosaic science.
The doctrine of metamorphosis of parts soon came to be regarded as of
fundamental importance.

But the doctrine had implications that few of its early advocates
realized. If all the parts of a flower--sepal, petal, stamen,
pistil, with their countless deviations of contour and color--are
but modifications of the leaf, such modification implies a marvellous
differentiation and development. To assert that a stamen is a
metamorphosed leaf means, if it means anything, that in the long sweep
of time the leaf has by slow or sudden gradations changed its character
through successive generations, until the offspring, so to speak, of a
true leaf has become a stamen. But if such a metamorphosis as this
is possible--if the seemingly wide gap between leaf and stamen may
be spanned by the modification of a line of organisms--where does the
possibility of modification of organic type find its bounds? Why may
not the modification of parts go on along devious lines until the remote
descendants of an organism are utterly unlike that organism? Why may we
not thus account for the development of various species of beings all
sprung from one parent stock? That, too, is a poet's dream; but is it
only a dream? Goethe thought not. Out of his studies of metamorphosis of
parts there grew in his mind the belief that the multitudinous species
of plants and animals about us have been evolved from fewer and fewer
earlier parent types, like twigs of a giant tree drawing their nurture
from the same primal root. It was a bold and revolutionary thought, and
the world regarded it as but the vagary of a poet.


Just at the time when this thought was taking form in Goethe's brain,
the same idea was germinating in the mind of another philosopher, an
Englishman of international fame, Dr. Erasmus Darwin, who, while he
lived, enjoyed the widest popularity as a poet, the rhymed couplets
of his Botanic Garden being quoted everywhere with admiration. And
posterity repudiating the verse which makes the body of the book,
yet grants permanent value to the book itself, because, forsooth, its
copious explanatory foot-notes furnish an outline of the status of
almost every department of science of the time.

But even though he lacked the highest art of the versifier, Darwin had,
beyond peradventure, the imagination of a poet coupled with profound
scientific knowledge; and it was his poetic insight, correlating
organisms seemingly diverse in structure and imbuing the lowliest flower
with a vital personality, which led him to suspect that there are no
lines of demarcation in nature. "Can it be," he queries, "that one
form of organism has developed from another; that different species
are really but modified descendants of one parent stock?" The alluring
thought nestled in his mind and was nurtured there, and grew in a fixed
belief, which was given fuller expression in his Zoonomia and in the
posthumous Temple of Nature.

Here is his rendering of the idea as versified in the Temple of Nature:

 "Organic life beneath the shoreless waves
  Was born, and nursed in Ocean's pearly caves;
  First forms minute, unseen by spheric glass,
  Move on the mud, or pierce the watery mass;
  These, as successive generations bloom,
  New powers acquire and larger limbs assume;
  Whence countless groups of vegetation spring,
  And breathing realms of fin, and feet, and wing.

 "Thus the tall Oak, the giant of the wood,
  Which bears Britannia's thunders on the flood;
  The Whale, unmeasured monster of the main;
  The lordly lion, monarch of the plain;
  The eagle, soaring in the realms of air,
  Whose eye, undazzled, drinks the solar glare;
  Imperious man, who rules the bestial crowd,
  Of language, reason, and reflection proud,
  With brow erect, who scorns this earthy sod,
  And styles himself the image of his God--
  Arose from rudiments of form and sense,
  An embryon point or microscopic ens!"(2)

Here, clearly enough, is the idea of evolution. But in that day there
was little proof forthcoming of its validity that could satisfy any
one but a poet, and when Erasmus Darwin died, in 1802, the idea of
transmutation of species was still but an unsubstantiated dream.

It was a dream, however, which was not confined to Goethe and Darwin.
Even earlier the idea had come more or less vaguely to another great
dreamer--and worker--of Germany, Immanuel Kant, and to several great
Frenchmen, including De Maillet, Maupertuis, Robinet, and the famous
naturalist Buffon--a man who had the imagination of a poet, though his
message was couched in most artistic prose. Not long after the middle of
the eighteenth century Buffon had put forward the idea of transmutation
of species, and he reiterated it from time to time from then on till
his death in 1788. But the time was not yet ripe for the idea of
transmutation of species to burst its bonds.

And yet this idea, in a modified or undeveloped form, had taken strange
hold upon the generation that was upon the scene at the close of the
eighteenth century. Vast numbers of hitherto unknown species of animals
had been recently discovered in previously unexplored regions of the
globe, and the wise men were sorely puzzled to account for the disposal
of all of these at the time of the deluge. It simplified matters greatly
to suppose that many existing species had been developed since the
episode of the ark by modification of the original pairs. The remoter
bearings of such a theory were overlooked for the time, and the idea
that American animals and birds, for example, were modified descendants
of Old-World forms--the jaguar of the leopard, the puma of the lion, and
so on--became a current belief with that class of humanity who accept
almost any statement as true that harmonizes with their prejudices
without realizing its implications.

Thus it is recorded with eclat that the discovery of the close proximity
of America at the northwest with Asia removes all difficulties as to the
origin of the Occidental faunas and floras, since Oriental species
might easily have found their way to America on the ice, and have been
modified as we find them by "the well-known influence of climate." And
the persons who gave expression to this idea never dreamed of its
real significance. In truth, here was the doctrine of evolution in a
nutshell, and, because its ultimate bearings were not clear, it seemed
the most natural of doctrines. But most of the persons who advanced it
would have turned from it aghast could they have realized its import.
As it was, however, only here and there a man like Buffon reasoned
far enough to inquire what might be the limits of such assumed
transmutation; and only here and there a Darwin or a Goethe reached the
conviction that there are no limits.


And even Goethe and Darwin had scarcely passed beyond that tentative
stage of conviction in which they held the thought of transmutation of
species as an ancillary belief not ready for full exposition. There was
one of their contemporaries, however, who, holding the same conception,
was moved to give it full explication. This was the friend and disciple
of Buffon, Jean Baptiste de Lamarck. Possessed of the spirit of a poet
and philosopher, this great Frenchman had also the widest range of
technical knowledge, covering the entire field of animate nature. The
first half of his long life was devoted chiefly to botany, in which he
attained high distinction. Then, just at the beginning of the nineteenth
century, he turned to zoology, in particular to the lower forms of
animal life. Studying these lowly organisms, existing and fossil, he
was more and more impressed with the gradations of form everywhere to be
seen; the linking of diverse families through intermediate ones; and
in particular with the predominance of low types of life in the earlier
geological strata. Called upon constantly to classify the various forms
of life in the course of his systematic writings, he found it more
and more difficult to draw sharp lines of demarcation, and at last the
suspicion long harbored grew into a settled conviction that there is
really no such thing as a species of organism in nature; that "species"
is a figment of the human imagination, whereas in nature there are only

That certain sets of individuals are more like one another than like
other sets is of course patent, but this only means, said Lamarck, that
these similar groups have had comparatively recent common ancestors,
while dissimilar sets of beings are more remotely related in
consanguinity. But trace back the lines of descent far enough, and all
will culminate in one original stock. All forms of life whatsoever are
modified descendants of an original organism. From lowest to highest,
then, there is but one race, one species, just as all the multitudinous
branches and twigs from one root are but one tree. For purposes of
convenience of description, we may divide organisms into orders,
families, genera, species, just as we divide a tree into root, trunk,
branches, twigs, leaves; but in the one case, as in the other, the
division is arbitrary and artificial.

In Philosophie Zoologique (1809), Lamarck first explicitly formulated
his ideas as to the transmutation of species, though he had outlined
them as early as 1801. In this memorable publication not only did he
state his belief more explicitly and in fuller detail than the idea
had been expressed by any predecessor, but he took another long forward
step, carrying him far beyond all his forerunners except Darwin, in
that he made an attempt to explain the way in which the transmutation of
species had been brought about. The changes have been wrought, he said,
through the unceasing efforts of each organism to meet the needs imposed
upon it by its environment. Constant striving means the constant use
of certain organs. Thus a bird running by the seashore is constantly
tempted to wade deeper and deeper in pursuit of food; its incessant
efforts tend to develop its legs, in accordance with the observed
principle that the use of any organ tends to strengthen and develop it.
But such slightly increased development of the legs is transmitted to
the off spring of the bird, which in turn develops its already improved
legs by its individual efforts, and transmits the improved tendency.
Generation after generation this is repeated, until the sum of the
infinitesimal variations, all in the same direction, results in the
production of the long-legged wading-bird. In a similar way, through
individual effort and transmitted tendency, all the diversified organs
of all creatures have been developed--the fin of the fish, the wing of
the bird, the hand of man; nay, more, the fish itself, the bird, the
man, even. Collectively the organs make up the entire organism; and what
is true of the individual organs must be true also of their ensemble,
the living being.

Whatever might be thought of Lamarck's explanation of the cause of
transmutation--which really was that already suggested by Erasmus
Darwin--the idea of the evolution for which he contended was but the
logical extension of the conception that American animals are the
modified and degenerated descendants of European animals. But people as
a rule are little prone to follow ideas to their logical conclusions,
and in this case the conclusions were so utterly opposed to the proximal
bearings of the idea that the whole thinking world repudiated them with
acclaim. The very persons who had most eagerly accepted the idea of
transmutation of European species into American species, and similar
limited variations through changed environment, because of the
relief thus given the otherwise overcrowded ark, were now foremost in
denouncing such an extension of the doctrine of transmutation as Lamarck

And, for that matter, the leaders of the scientific world were equally
antagonistic to the Lamarckian hypothesis. Cuvier in particular, once
the pupil of Lamarck, but now his colleague, and in authority more than
his peer, stood out against the transmutation doctrine with all his
force. He argued for the absolute fixity of species, bringing to bear
the resources of a mind which, as a mere repository of facts, perhaps
never was excelled. As a final and tangible proof of his position,
he brought forward the bodies of ibises that had been embalmed by the
ancient Egyptians, and showed by comparison that these do not differ in
the slightest particular from the ibises that visit the Nile to-day.

Cuvier's reasoning has such great historical interest--being the
argument of the greatest opponent of evolution of that day--that we
quote it at some length.

"The following objections," he says, "have already been started against
my conclusions. Why may not the presently existing races of mammiferous
land quadrupeds be mere modifications or varieties of those ancient
races which we now find in the fossil state, which modifications may
have been produced by change of climate and other local circumstances,
and since raised to the present excessive difference by the operations
of similar causes during a long period of ages?

"This objection may appear strong to those who believe in the indefinite
possibility of change of form in organized bodies, and think that,
during a succession of ages and by alterations of habitudes, all the
species may change into one another, or one of them give birth to all
the rest. Yet to these persons the following answer may be given from
their own system: If the species have changed by degrees, as they
assume, we ought to find traces of this gradual modification. Thus,
between the palaeotherium and the species of our own day, we should be
able to discover some intermediate forms; and yet no such discovery
has ever been made. Since the bowels of the earth have not preserved
monuments of this strange genealogy, we have no right to conclude that
the ancient and now extinct species were as permanent in their forms
and characters as those which exist at present; or, at least, that the
catastrophe which destroyed them did not leave sufficient time for the
productions of the changes that are alleged to have taken place.

"In order to reply to those naturalists who acknowledge that the
varieties of animals are restrained by nature within certain limits,
it would be necessary to examine how far these limits extend. This is
a very curious inquiry, and in itself exceedingly interesting under
a variety of relations, but has been hitherto very little attended

"Wild animals which subsist upon herbage feel the influence of climate a
little more extensively, because there is added to it the influence
of food, both in regard to its abundance and its quality. Thus the
elephants of one forest are larger than those of another; their tusks
also grow somewhat longer in places where their food may happen to be
more favorable for the production of the substance of ivory. The same
may take place in regard to the horns of stags and reindeer. But let
us examine two elephants, the most dissimilar that can be conceived,
we shall not discover the smallest difference in the number and
articulations of the bones, the structure of the teeth, etc.........

"Nature appears also to have guarded against the alterations of species
which might proceed from mixture of breeds by influencing the various
species of animals with mutual aversion from one another. Hence all
the cunning and all the force that man is able to exert is necessary
to accomplish such unions, even between species that have the nearest
resemblances. And when the mule breeds that are thus produced by these
forced conjunctions happen to be fruitful, which is seldom the case,
this fecundity never continues beyond a few generations, and would not
probably proceed so far without a continuance of the same cares which
excited it at first. Thus we never see in a wild state intermediate
productions between the hare and the rabbit, between the stag and the
doe, or between the marten and the weasel. But the power of man changes
this established order, and continues to produce all these intermixtures
of which the various species are susceptible, but which they would never
produce if left to themselves.

"The degrees of these variations are proportional to the intensity of
the causes that produced them--namely, the slavery or subjection
under which those animals are to man. They do not proceed far in
half-domesticated species. In the cat, for example, a softer or harsher
fur, more brilliant or more varied colors, greater or less size--these
form the whole extent of variety in the species; the skeleton of the
cat of Angora differs in no regular and constant circumstances from the
wild-cat of Europe...."

The most remarkable effects of the influence of man are produced upon
that animal which he has reduced most completely under subjection. Dogs
have been transported by mankind into every part of the world and have
submitted their action to his entire direction. Regulated in their
unions by the pleasure or caprice of their masters, the almost endless
varieties of dogs differ from one another in color, in length, and
abundance of hair, which is sometimes entirely wanting; in their natural
instincts; in size, which varies in measure as one to five, mounting in
some instances to more than a hundredfold in bulk; in the form of their
ears, noses, and tails; in the relative length of their legs; in the
progressive development of the brain, in several of the domesticated
varieties occasioning alterations even in the form of the head, some of
them having long, slender muzzles with a flat forehead, others having
short muzzles with a forehead convex, etc., insomuch that the apparent
difference between a mastiff and a water-spaniel and between a greyhound
and a pugdog are even more striking than between almost any of the wild
species of a genus........

It follows from these observations that animals have certain fixed and
natural characters which resist the effects of every kind of influence,
whether proceeding from natural causes or human interference; and we
have not the smallest reason to suspect that time has any more effect on
them than climate.

"I am aware that some naturalists lay prodigious stress upon the
thousands which they can call into action by a dash of their pens. In
such matters, however, our only way of judging as to the effects which
may be produced by a long period of time is by multiplying, as it were,
such as are produced by a shorter time. With this view I have endeavored
to collect all the ancient documents respecting the forms of animals;
and there are none equal to those furnished by the Egyptians, both in
regard to their antiquity and abundance. They have not only left us
representatives of animals, but even their identical bodies embalmed and
preserved in the catacombs.

"I have examined, with the greatest attention, the engraved figures of
quadrupeds and birds brought from Egypt to ancient Rome, and all these
figures, one with another, have a perfect resemblance to their intended
objects, such as they still are to-day.

"From all these established facts, there does not seem to be the
smallest foundation for supposing that the new genera which I have
discovered or established among extraneous fossils, such as the
paleoetherium, anoplotherium, megalonyx, mastodon, pterodactylis, etc.,
have ever been the sources of any of our present animals, which only
differ so far as they are influenced by time or climate. Even if it
should prove true, which I am far from believing to be the case, that
the fossil elephants, rhinoceroses, elks, and bears do not differ
further from the existing species of the same genera than the present
races of dogs differ among themselves, this would by no means be a
sufficient reason to conclude that they were of the same species; since
the races or varieties of dogs have been influenced by the trammels
of domesticity, which those other animals never did, and indeed never
could, experience."(3)

To Cuvier's argument from the fixity of Egyptian mummified birds and
animals, as above stated, Lamarck replied that this proved nothing
except that the ibis had become perfectly adapted to its Egyptian
surroundings in an early day, historically speaking, and that the
climatic and other conditions of the Nile Valley had not since then
changed. His theory, he alleged, provided for the stability of species
under fixed conditions quite as well as for transmutation under varying

But, needless to say, the popular verdict lay with Cuvier; talent won
for the time against genius, and Lamarck was looked upon as an impious
visionary. His faith never wavered, however. He believed that he had
gained a true insight into the processes of animate nature, and
he reiterated his hypotheses over and over, particularly in the
introduction to his Histoire Naturelle des Animaux sans Vertebres, in
1815, and in his Systeme des Connaissances Positives de l'Homme, in
1820. He lived on till 1829, respected as a naturalist, but almost
unrecognized as a prophet.


While the names of Darwin and Goethe, and in particular that of Lamarck,
must always stand out in high relief in this generation as the exponents
of the idea of transmutation of species, there are a few others which
must not be altogether overlooked in this connection. Of these the
most conspicuous is that of Gottfried Reinhold Treviranus, a German
naturalist physician, professor of mathematics in the lyceum at Bremen.

It was an interesting coincidence that Treviranus should have published
the first volume of his Biologie, oder Philosophie der lebenden Natur,
in which his views on the transmutation of species were expounded, in
1802, the same twelvemonth in which Lamarck's first exposition of the
same doctrine appeared in his Recherches sur l'Organisation des Corps
Vivants. It is singular, too, that Lamarck, in his Hydrogelogie of
the same date, should independently have suggested "biology" as an
appropriate word to express the general science of living things. It is
significant of the tendency of thought of the time that the need of
such a unifying word should have presented itself simultaneously to
independent thinkers in different countries.

That same memorable year, Lorenz Oken, another philosophical naturalist,
professor in the University of Zurich, published the preliminary
outlines of his Philosophie der Natur, which, as developed through
later publications, outlined a theory of spontaneous generation and of
evolution of species. Thus it appears that this idea was germinating
in the minds of several of the ablest men of the time during the
first decade of our century. But the singular result of their various
explications was to give sudden check to that undercurrent of thought
which for some time had been setting towards this conception. As soon as
it was made clear whither the concession that animals may be changed
by their environment must logically trend, the recoil from the idea
was instantaneous and fervid. Then for a generation Cuvier was almost
absolutely dominant, and his verdict was generally considered final.

There was, indeed, one naturalist of authority in France who had the
hardihood to stand out against Cuvier and his school, and who was in a
position to gain a hearing, though by no means to divide the following.
This was Etienne Geoffroy Saint-Hilaire, the famous author of the
Philosophie Anatomique, and for many years the colleague of Lamarck
at the Jardin des Plantes. Like Goethe, Geoffroy was pre-eminently an
anatomist, and, like the great German, he had early been impressed with
the resemblances between the analogous organs of different classes of
beings. He conceived the idea that an absolute unity of type prevails
throughout organic nature as regards each set of organs. Out of this
idea grew his gradually formed belief that similarity of structure might
imply identity of origin--that, in short, one species of animal might
have developed from another.

Geoffroy's grasp of this idea of transmutation was by no means so
complete as that of Lamarck, and he seems never to have fully determined
in his own mind just what might be the limits of such development of
species. Certainly he nowhere includes all organic creatures in one line
of descent, as Lamarck had done; nevertheless, he held tenaciously to
the truth as he saw it, in open opposition to Cuvier, with whom he held
a memorable debate at the Academy of Sciences in 1830--the debate which
so aroused the interest and enthusiasm of Goethe, but which, in the
opinion of nearly every one else, resulted in crushing defeat for
Geoffrey, and brilliant, seemingly final, victory for the advocate of
special creation and the fixity of species.

With that all ardent controversy over the subject seemed to end, and
for just a quarter of a century to come there was published but a
single argument for transmutation of species which attracted any general
attention whatever. This oasis in a desert generation was a little
book called Vestiges of the Natural History of Creation, which appeared
anonymously in England in 1844, and which passed through numerous
editions, and was the subject of no end of abusive and derisive comment.
This book, the authorship of which remained for forty years a secret,
is now conceded to have been the work of Robert Chambers, the well-known
English author and publisher. The book itself is remarkable as being an
avowed and unequivocal exposition of a general doctrine of evolution,
its view being as radical and comprehensive as that of Lamarck himself.
But it was a resume of earlier efforts rather than a new departure, to
say nothing of its technical shortcomings, which may best be illustrated
by a quotation.

"The whole question," says Chambers, "stands thus: For the theory of
universal order--that is, order as presiding in both the origin and
administration of the world--we have the testimony of a vast number of
facts in nature, and this one in addition--that whatever is left from
the domain of ignorance, and made undoubted matter of science, forms a
new support to the same doctrine. The opposite view, once predominant,
has been shrinking for ages into lesser space, and now maintains a
footing only in a few departments of nature which happen to be less
liable than others to a clear investigation. The chief of these, if not
almost the only one, is the origin of the organic kingdoms. So long as
this remains obscure, the supernatural will have a certain hold upon
enlightened persons. Should it ever be cleared up in a way that leaves
no doubt of a natural origin of plants and animals, there must be a
complete revolution in the view which is generally taken of the relation
of the Father of our being.

"This prepares the way for a few remarks on the present state of opinion
with regard to the origin of organic nature. The great difficulty here
is the apparent determinateness of species. These forms of life being
apparently unchangeable, or at least always showing a tendency to return
to the character from which they have diverged, the idea arises that
there can have been no progression from one to another; each must have
taken its special form, independently of other forms, directly from the
appointment of the Creator. The Edinburgh Review writer says, 'they were
created by the hand of God and adapted to the conditions of the period.'
Now it is, in the first place, not certain that species constantly
maintain a fixed character, for we have seen that what were long
considered as determinate species have been transmuted into others.
Passing, however, from this fact, as it is not generally received among
men of science, there remain some great difficulties in connection
with the idea of special creation. First we should have to suppose, as
pointed out in my former volume, a most startling diversity of plan
in the divine workings, a great general plan or system of law in the
leading events of world-making, and a plan of minute, nice operation,
and special attention in some of the mere details of the process. The
discrepancy between the two conceptions is surely overpowering, when we
allow ourselves to see the whole matter in a steady and rational light.
There is, also, the striking fact of an ascertained historical progress
of plants and animals in the order of their organization; marine and
cellular plants and invertebrated animals first, afterwards higher
examples of both. In an arbitrary system we had surely no reason to
expect mammals after reptiles; yet in this order they came. The writer
in the Edinburgh Review speaks of animals as coming in adaptation to
conditions, but this is only true in a limited sense. The groves which
formed the coal-beds might have been a fitting habitation for reptiles,
birds, and mammals, as such groves are at the present day; yet we see
none of the last of these classes and hardly any traces of the two first
at that period of the earth. Where the iguanodon lived the elephant
might have lived, but there was no elephant at that time. The sea of the
Lower Silurian era was capable of supporting fish, but no fish existed.
It hence forcibly appears that theatres of life must have remained
unserviceable, or in the possession of a tenantry inferior to what might
have enjoyed them, for many ages: there surely would have been no such
waste allowed in a system where Omnipotence was working upon the plan
of minute attention to specialities. The fact seems to denote that the
actual procedure of the peopling of the earth was one of a natural kind,
requiring a long space of time for its evolution. In this supposition
the long existence of land without land animals, and more particularly
without the noblest classes and orders, is only analogous to the fact,
not nearly enough present to the minds of a civilized people, that to
this day the bulk of the earth is a waste as far as man is concerned.

"Another startling objection is in the infinite local variation of
organic forms. Did the vegetable and animal kingdoms consist of a
definite number of species adapted to peculiarities of soil and climate,
and universally distributed, the fact would be in harmony with the
idea of special exertion. But the truth is that various regions exhibit
variations altogether without apparent end or purpose. Professor Henslow
enumerates forty-five distinct flowers or sets of plants upon the
surface of the earth, notwithstanding that many of these would be
equally suitable elsewhere. The animals of different continents are
equally various, few species being the same in any two, though the
general character may conform. The inference at present drawn from this
fact is that there must have been, to use the language of the Rev. Dr.
Pye Smith, 'separate and original creations, perhaps at different and
respectively distinct epochs.' It seems hardly conceivable that rational
men should give an adherence to such a doctrine when we think of what it
involves. In the single fact that it necessitates a special fiat of the
inconceivable Author of this sand-cloud of worlds to produce the flora
of St. Helena, we read its more than sufficient condemnation. It surely
harmonizes far better with our general ideas of nature to suppose that,
just as all else in this far-spread science was formed on the laws
impressed upon it at first by its Author, so also was this. An exception
presented to us in such a light appears admissible only when we succeed
in forbidding our minds to follow out those reasoning processes to
which, by another law of the Almighty, they tend, and for which they are

Such reasoning as this naturally aroused bitter animadversions, and
cannot have been without effect in creating an undercurrent of thought
in opposition to the main trend of opinion of the time. But the book can
hardly be said to have done more than that. Indeed, some critics
have denied it even this merit. After its publication, as before,
the conception of transmutation of species remained in the popular
estimation, both lay and scientific, an almost forgotten "heresy."

It is true that here and there a scientist of greater or less repute--as
Von Buch, Meckel, and Von Baer in Germany, Bory Saint-Vincent in
France, Wells, Grant, and Matthew in England, and Leidy in America--had
expressed more or less tentative dissent from the doctrine of
special creation and immutability of species, but their unaggressive
suggestions, usually put forward in obscure publications, and
incidentally, were utterly overlooked and ignored. And so, despite the
scientific advances along many lines at the middle of the century, the
idea of the transmutability of organic races had no such prominence,
either in scientific or unscientific circles, as it had acquired fifty
years before. Special creation held the day, seemingly unopposed.


But even at this time the fancied security of the special-creation
hypothesis was by no means real. Though it seemed so invincible, its
real position was that of an apparently impregnable fortress beneath
which, all unbeknown to the garrison, a powder-mine has been dug and
lies ready for explosion. For already there existed in the secluded
work-room of an English naturalist, a manuscript volume and a portfolio
of notes which might have sufficed, if given publicity, to shatter the
entire structure of the special-creation hypothesis. The naturalist who,
by dint of long and patient effort, had constructed this powder-mine of
facts was Charles Robert Darwin, grandson of the author of Zoonomia.

As long ago as July 1, 1837, young Darwin, then twenty-eight years of
age, had opened a private journal, in which he purposed to record all
facts that came to him which seemed to have any bearing on the moot
point of the doctrine of transmutation of species. Four or five years
earlier, during the course of that famous trip around the world with
Admiral Fitzroy, as naturalist to the Beagle, Darwin had made the
personal observations which first tended to shake his belief of the
fixity of species. In South America, in the Pampean formation, he had
discovered "great fossil animals covered with armor like that on the
existing armadillos," and had been struck with this similarity of type
between ancient and existing faunas of the same region. He was also
greatly impressed by the manner in which closely related species of
animals were observed to replace one another as he proceeded southward
over the continent; and "by the South-American character of most of the
productions of the Galapagos Archipelago, and more especially by the
manner in which they differ slightly on each island of the group, none
of the islands appearing to be very ancient in a geological sense."

At first the full force of these observations did not strike him; for,
under sway of Lyell's geological conceptions, he tentatively explained
the relative absence of life on one of the Galapagos Islands by
suggesting that perhaps no species had been created since that island
arose. But gradually it dawned upon him that such facts as he had
observed "could only be explained on the supposition that species
gradually become modified." From then on, as he afterwards asserted, the
subject haunted him; hence the journal of 1837.

It will thus be seen that the idea of the variability of species came to
Charles Darwin as an inference from personal observations in the field,
not as a thought borrowed from books. He had, of course, read the works
of his grandfather much earlier in life, but the arguments of Zoonomia
and The Temple of Nature had not served in the least to weaken his
acceptance of the current belief in fixity of species. Nor had he been
more impressed with the doctrine of Lamarck, so closely similar to that
of his grandfather. Indeed, even after his South-American experience had
aroused him to a new point of view he was still unable to see anything
of value in these earlier attempts at an explanation of the variation
of species. In opening his journal, therefore, he had no preconceived
notion of upholding the views of these or any other makers of
hypotheses, nor at the time had he formulated any hypothesis of his own.
His mind was open and receptive; he was eager only for facts which might
lead him to an understanding of a problem which seemed utterly obscure.
It was something to feel sure that species have varied; but how have
such variations been brought about?

It was not long before Darwin found a clew which he thought might
lead to the answer he sought. In casting about for facts he had soon
discovered that the most available field for observation lay among
domesticated animals, whose numerous variations within specific lines
are familiar to every one. Thus under domestication creatures so
tangibly different as a mastiff and a terrier have sprung from a
common stock. So have the Shetland pony, the thoroughbred, and the
draught-horse. In short, there is no domesticated animal that has not
developed varieties deviating more or less widely from the parent stock.
Now, how has this been accomplished? Why, clearly, by the preservation,
through selective breeding, of seemingly accidental variations. Thus
one horseman, by constantly selecting animals that "chance" to have
the right build and stamina, finally develops a race of running-horses;
while another horseman, by selecting a different series of progenitors,
has developed a race of slow, heavy draught animals.

So far, so good; the preservation of "accidental" variations through
selective breeding is plainly a means by which races may be developed
that are very different from their original parent form. But this
is under man's supervision and direction. By what process could such
selection be brought about among creatures in a state of nature? Here
surely was a puzzle, and one that must be solved before another step
could be taken in this direction.

The key to the solution of this puzzle came into Darwin's mind through
a chance reading of the famous essay on "Population" which Thomas
Robert Malthus had published almost half a century before. This
essay, expositing ideas by no means exclusively original with Malthus,
emphasizes the fact that organisms tend to increase at a geometrical
ratio through successive generations, and hence would overpopulate the
earth if not somehow kept in check. Cogitating this thought, Darwin
gained a new insight into the processes of nature. He saw that in virtue
of this tendency of each race of beings to overpopulate the earth,
the entire organic world, animal and vegetable, must be in a state of
perpetual carnage and strife, individual against individual, fighting
for sustenance and life.

That idea fully imagined, it becomes plain that a selective influence
is all the time at work in nature, since only a few individuals,
relatively, of each generation can come to maturity, and these few
must, naturally, be those best fitted to battle with the particular
circumstances in the midst of which they are placed. In other words, the
individuals best adapted to their surroundings will, on the average, be
those that grow to maturity and produce offspring. To these
offspring will be transmitted the favorable peculiarities. Thus these
peculiarities will become permanent, and nature will have accomplished
precisely what the human breeder is seen to accomplish. Grant that
organisms in a state of nature vary, however slightly, one from another
(which is indubitable), and that such variations will be transmitted by
a parent to its offspring (which no one then doubted); grant, further,
that there is incessant strife among the various organisms, so that
only a small proportion can come to maturity--grant these things, said
Darwin, and we have an explanation of the preservation of variations
which leads on to the transmutation of species themselves.

This wonderful coign of vantage Darwin had reached by 1839. Here was the
full outline of his theory; here were the ideas which afterwards came to
be embalmed in familiar speech in the phrases "spontaneous variation,"
and the "survival of the fittest," through "natural selection." After
such a discovery any ordinary man would at once have run through the
streets of science, so to speak, screaming "Eureka!" Not so Darwin. He
placed the manuscript outline of his theory in his portfolio, and went
on gathering facts bearing on his discovery. In 1844 he made an abstract
in a manuscript book of the mass of facts by that time accumulated.
He showed it to his friend Hooker, made careful provision for its
publication in the event of his sudden death, then stored it away in
his desk and went ahead with the gathering of more data. This was the
unexploded powder-mine to which I have just referred.

Twelve years more elapsed--years during which the silent worker gathered
a prodigious mass of facts, answered a multitude of objections that
arose in his own mind, vastly fortified his theory. All this time
the toiler was an invalid, never knowing a day free from illness and
discomfort, obliged to husband his strength, never able to work more
than an hour and a half at a stretch; yet he accomplished what would
have been vast achievements for half a dozen men of robust health. Two
friends among the eminent scientists of the day knew of his labors--Sir
Joseph Hooker, the botanist, and Sir Charles Lyell, the geologist.
Gradually Hooker had come to be more than half a convert to Darwin's
views. Lyell was still sceptical, yet he urged Darwin to publish his
theory without further delay lest he be forestalled. At last the patient
worker decided to comply with this advice, and in 1856 he set to work to
make another and fuller abstract of the mass of data he had gathered.

And then a strange thing happened. After Darwin had been at work on his
"abstract" about two years, but before he had published a line of it,
there came to him one day a paper in manuscript, sent for his approval
by a naturalist friend named Alfred Russel Wallace, who had been for
some time at work in the East India Archipelago. He read the paper, and,
to his amazement, found that it contained an outline of the same theory
of "natural selection" which he himself had originated and for twenty
years had worked upon. Working independently, on opposite sides of the
globe, Darwin and Wallace had hit upon the same explanation of the cause
of transmutation of species. "Were Wallace's paper an abstract of my
unpublished manuscript of 1844," said Darwin, "it could not better
express my ideas."

Here was a dilemma. To publish this paper with no word from Darwin would
give Wallace priority, and wrest from Darwin the credit of a discovery
which he had made years before his codiscoverer entered the field. Yet,
on the other hand, could Darwin honorably do otherwise than publish his
friend's paper and himself remain silent? It was a complication well
calculated to try a man's soul. Darwin's was equal to the test. Keenly
alive to the delicacy of the position, he placed the whole matter before
his friends Hooker and Lyell, and left the decision as to a course of
action absolutely to them. Needless to say, these great men did the one
thing which insured full justice to all concerned. They counselled a
joint publication, to include on the one hand Wallace's paper, and on
the other an abstract of Darwin's ideas, in the exact form in which it
had been outlined by the author in a letter to Asa Gray in the previous
year--an abstract which was in Gray's hands before Wallace's paper was
in existence. This joint production, together with a full statement of
the facts of the case, was presented to the Linnaean Society of London
by Hooker and Lyell on the evening of July 1, 1858, this being, by an
odd coincidence, the twenty-first anniversary of the day on which
Darwin had opened his journal to collect facts bearing on the "species
question." Not often before in the history of science has it happened
that a great theory has been nurtured in its author's brain through
infancy and adolescence to its full legal majority before being sent out
into the world.

Thus the fuse that led to the great powder-mine had been lighted. The
explosion itself came more than a year later, in November, 1859, when
Darwin, after thirteen months of further effort, completed the outline
of his theory, which was at first begun as an abstract for the Linnaean
Society, but which grew to the size of an independent volume despite
his efforts at condensation, and which was given that ever-to-be-famous
title, The Origin of Species by Means of Natural Selection, or the
Preservation of Favored Races in the Struggle for Life. And what an
explosion it was! The joint paper of 1858 had made a momentary flare,
causing the hearers, as Hooker said, to "speak of it with bated breath,"
but beyond that it made no sensation. What the result was when the
Origin itself appeared no one of our generation need be told. The rumble
and roar that it made in the intellectual world have not yet altogether
ceased to echo after more than forty years of reverberation.


To the Origin of Species, then, and to its author, Charles Darwin,
must always be ascribed chief credit for that vast revolution in the
fundamental beliefs of our race which has come about since 1859, and
which made the second half of the century memorable. But it must not be
overlooked that no such sudden metamorphosis could have been effected
had it not been for the aid of a few notable lieutenants, who rallied
to the standards of the leader immediately after the publication of the
Origin. Darwin had all along felt the utmost confidence in the ultimate
triumph of his ideas. "Our posterity," he declared, in a letter to
Hooker, "will marvel as much about the current belief (in special
creation) as we do about fossil shells having been thought to be created
as we now see them." But he fully realized that for the present success
of his theory of transmutation the championship of a few leaders of
science was all-essential. He felt that if he could make converts of
Hooker and Lyell and of Thomas Henry Huxley at once, all would be well.

His success in this regard, as in others, exceeded his expectations.
Hooker was an ardent disciple from reading the proof-sheets before the
book was published; Lyell renounced his former beliefs and fell into
line a few months later; while Huxley, so soon as he had mastered
the central idea of natural selection, marvelled that so simple yet
all-potent a thought had escaped him so long, and then rushed eagerly
into the fray, wielding the keenest dialectic blade that was drawn
during the entire controversy. Then, too, unexpected recruits were found
in Sir John Lubbock and John Tyndall, who carried the war eagerly into
their respective territories; while Herbert Spencer, who had advocated
a doctrine of transmutation on philosophic grounds some years before
Darwin published the key to the mystery--and who himself had barely
escaped independent discovery of that key--lent his masterful influence
to the cause. In America the famous botanist Asa Gray, who had long been
a correspondent of Darwin's but whose advocacy of the new theory had not
been anticipated, became an ardent propagandist; while in Germany Ernst
Heinrich Haeckel, the youthful but already noted zoologist, took up the
fight with equal enthusiasm.

Against these few doughty champions--with here and there another of less
general renown--was arrayed, at the outset, practically all Christendom.
The interest of the question came home to every person of intelligence,
whatever his calling, and the more deeply as it became more and more
clear how far-reaching are the real bearings of the doctrine of natural
selection. Soon it was seen that should the doctrine of the survival
of the favored races through the struggle for existence win, there must
come with it as radical a change in man's estimate of his own position
as had come in the day when, through the efforts of Copernicus and
Galileo, the world was dethroned from its supposed central position in
the universe. The whole conservative majority of mankind recoiled from
this necessity with horror. And this conservative majority included not
laymen merely, but a vast preponderance of the leaders of science also.

With the open-minded minority, on the other hand, the theory of
natural selection made its way by leaps and bounds. Its delightful
simplicity--which at first sight made it seem neither new nor
important--coupled with the marvellous comprehensiveness of its
implications, gave it a hold on the imagination, and secured it a
hearing where other theories of transmutation of species had been
utterly scorned. Men who had found Lamarck's conception of change
through voluntary effort ridiculous, and the vaporings of the Vestiges
altogether despicable, men whose scientific cautions held them back
from Spencer's deductive argument, took eager hold of that tangible,
ever-present principle of natural selection, and were led on and on to
its goal. Hour by hour the attitude of the thinking world towards this
new principle changed; never before was so great a revolution wrought so

Nor was this merely because "the times were ripe" or "men's minds
prepared for evolution." Darwin himself bears witness that this was not
altogether so. All through the years in which he brooded this theory he
sounded his scientific friends, and could find among them not one
who acknowledged a doctrine of transmutation. The reaction from the
stand-point of Lamarck and Erasmus Darwin and Goethe had been complete,
and when Charles Darwin avowed his own conviction he expected always
to have it met with ridicule or contempt. In 1857 there was but one
man speaking with any large degree of authority in the world who openly
avowed a belief in transmutation of species--that man being Herbert
Spencer. But the Origin of Species came, as Huxley has said, like a
flash in the darkness, enabling the benighted voyager to see the way.
The score of years during which its author had waited and worked
had been years well spent. Darwin had become, as he himself says, a
veritable Croesus, "overwhelmed with his riches in facts"--facts of
zoology, of selective artificial breeding, of geographical distribution
of animals, of embryology, of paleontology. He had massed his facts
about his theory, condensed them and recondensed, until his volume of
five hundred pages was an encyclopaedia in scope. During those long
years of musing he had thought out almost every conceivable objection to
his theory, and in his book every such objection was stated with fullest
force and candor, together with such reply as the facts at command
might dictate. It was the force of those twenty years of effort of
a master-mind that made the sudden breach in the breaswtork{sic} of
current thought.

Once this breach was effected the work of conquest went rapidly on. Day
by day squads of the enemy capitulated and struck their arms. By the
time another score of years had passed the doctrine of evolution had
become the working hypothesis of the scientific world. The revolution
had been effected.

And from amid the wreckage of opinion and belief stands forth the figure
of Charles Darwin, calm, imperturbable, serene; scatheless to ridicule,
contumely, abuse; unspoiled by ultimate success; unsullied alike by
the strife and the victory--take him for all in all, for character, for
intellect, for what he was and what he did, perhaps the most Socratic
figure of the century. When, in 1882, he died, friend and foe alike
conceded that one of the greatest sons of men had rested from his
labors, and all the world felt it fitting that the remains of Charles
Darwin should be entombed in Westminster Abbey close beside the honored
grave of Isaac Newton. Nor were there many who would dispute the justice
of Huxley's estimate of his accomplishment: "He found a great truth
trodden under foot. Reviled by bigots, and ridiculed by all the world,
he lived long enough to see it, chiefly by his own efforts, irrefragably
established in science, inseparably incorporated with the common
thoughts of men, and only hated and feared by those who would revile but
dare not."


Wide as are the implications of the great truth which Darwin and his
co-workers established, however, it leaves quite untouched the problem
of the origin of those "favored variations" upon which it operates.
That such variations are due to fixed and determinate causes no one
understood better than Darwin; but in his original exposition of his
doctrine he made no assumption as to what these causes are. He accepted
the observed fact of variation--as constantly witnessed, for example, in
the differences between parents and offspring--and went ahead from this

But as soon as the validity of the principle of natural selection came
to be acknowledged speculators began to search for the explanation of
those variations which, for purposes of argument, had been provisionally
called "spontaneous." Herbert Spencer had all along dwelt on this phase
of the subject, expounding the Lamarckian conceptions of the direct
influence of the environment (an idea which had especially appealed
to Buffon and to Geoffroy Saint-Hilaire), and of effort in response to
environment and stimulus as modifying the individual organism, and thus
supplying the basis for the operation of natural selection. Haeckel also
became an advocate of this idea, and presently there arose a so-called
school of neo-Lamarckians, which developed particular strength and
prominence in America under the leadership of Professors A. Hyatt and E.
D. Cope.

But just as the tide of opinion was turning strongly in this direction,
an utterly unexpected obstacle appeared in the form of the theory of
Professor August Weismann, put forward in 1883, which antagonized the
Lamarckian conception (though not touching the Darwinian, of which
Weismann is a firm upholder) by denying that individual variations,
however acquired by the mature organism, are transmissible. The
flurry which this denial created has not yet altogether subsided, but
subsequent observations seem to show that it was quite disproportionate
to the real merits of the case. Notwithstanding Professor Weismann's
objections, the balance of evidence appears to favor the view that the
Lamarckian factor of acquired variations stands as the complement of the
Darwinian factor of natural selection in effecting the transmutation of

Even though this partial explanation of what Professor Cope calls the
"origin of the fittest" be accepted, there still remains one great life
problem which the doctrine of evolution does not touch. The origin
of species, genera, orders, and classes of beings through endless
transmutations is in a sense explained; but what of the first term of
this long series? Whence came that primordial organism whose transmuted
descendants make up the existing faunas and floras of the globe?

There was a time, soon after the doctrine of evolution gained a hearing,
when the answer to that question seemed to some scientists of authority
to have been given by experiment. Recurring to a former belief, and
repeating some earlier experiments, the director of the Museum of
Natural History at Rouen, M. F. A. Pouchet, reached the conclusion that
organic beings are spontaneously generated about us constantly, in the
familiar processes of putrefaction, which were known to be due to the
agency of microscopic bacteria. But in 1862 Louis Pasteur proved that
this seeming spontaneous generation is in reality due to the existence
of germs in the air. Notwithstanding the conclusiveness of these
experiments, the claims of Pouchet were revived in England ten years
later by Professor Bastian; but then the experiments of John Tyndall,
fully corroborating the results of Pasteur, gave a final quietus to the
claim of "spontaneous generation" as hitherto formulated.

There for the moment the matter rests. But the end is not yet. Fauna
and flora are here, and, thanks to Lamarck and Wallace and Darwin, their
development, through the operation of those "secondary causes" which we
call laws of nature, has been proximally explained. The lowest forms of
life have been linked with the highest in unbroken chains of descent.
Meantime, through the efforts of chemists and biologists, the gap
between the inorganic and the organic worlds, which once seemed almost
infinite, has been constantly narrowed. Already philosophy can throw
a bridge across that gap. But inductive science, which builds its own
bridges, has not yet spanned the chasm, small though it appear. Until
it shall have done so, the bridge of organic evolution is not quite
complete; yet even as it stands to-day it is perhaps the most stupendous
scientific structure of the nineteenth century.



At least two pupils of William Harvey distinguished themselves in
medicine, Giorgio Baglivi (1669-1707), who has been called the "Italian
Sydenham," and Hermann Boerhaave (1668-1738). The work of Baglivi was
hardly begun before his early death removed one of the most promising of
the early eighteenth-century physicians. Like Boerhaave, he represents a
type of skilled, practical clinitian rather than the abstract scientist.
One of his contributions to medical literature is the first accurate
description of typhoid, or, as he calls it, mesenteric fever.

If for nothing else, Boerhaave must always be remembered as the teacher
of Von Haller, but in his own day he was the widest known and the most
popular teacher in the medical world. He was the idol of his pupils
at Leyden, who flocked to his lectures in such numbers that it became
necessary to "tear down the walls of Leyden to accommodate them." His
fame extended not only all over Europe but to Asia, North America, and
even into South America. A letter sent him from China was addressed
to "Boerhaave in Europe." His teachings represent the best medical
knowledge of his day, a high standard of morality, and a keen
appreciation of the value of observation; and it was through such
teachings imparted to his pupils and advanced by them, rather than to
any new discoveries, that his name is important in medical history. His
arrangement and classification of the different branches of medicine
are interesting as representing the attitude of the medical profession
towards these various branches at that time.

"In the first place we consider Life; then Health, afterwards Diseases;
and lastly their several Remedies.

"Health the first general branch of Physic in our Institutions is termed
Physiology, or the Animal Oeconomy; demonstrating the several Parts of
the human Body, with their Mechanism and Actions.

"The second branch of Physic is called Pathology, treating of Diseases,
their Differences, Causes and Effects, or Symptoms; by which the human
Body is known to vary from its healthy state.

"The third part of Physic is termed Semiotica, which shows the Signs
distinguishing between sickness and Health, Diseases and their Causes
in the human Body; it also imports the State and Degrees of Health and
Diseases, and presages their future Events.

"The fourth general branch of Physic is termed Hygiene, or Prophylaxis.

"The fifth and last part of Physic is called Therapeutica; which
instructs us in the Nature, Preparation and uses of the Materia Medica;
and the methods of applying the same, in order to cure Diseases and
restore lost Health."(1)

From this we may gather that his general view of medicine was not unlike
that taken at the present time.

Boerhaave's doctrines were arranged into a "system" by Friedrich
Hoffmann, of Halle (1660-1742), this system having the merit of being
simple and more easily comprehended than many others. In this system
forces were considered inherent in matter, being expressed as mechanical
movements, and determined by mass, number, and weight. Similarly, forces
express themselves in the body by movement, contraction, and relaxation,
etc., and life itself is movement, "particularly movement of the
heart." Life and death are, therefore, mechanical phenomena, health is
determined by regularly recurring movements, and disease by irregularity
of them. The body is simply a large hydraulic machine, controlled by
"the aether" or "sensitive soul," and the chief centre of this soul lies
in the medulla.

In the practical application of medicines to diseases Hoffman used
simple remedies, frequently with happy results, for whatever the
medical man's theory may be he seldom has the temerity to follow it out
logically, and use the remedies indicated by his theory to the exclusion
of long-established, although perhaps purely empirical, remedies.
Consequently, many vague theorists have been excellent practitioners,
and Hoffman was one of these. Some of the remedies he introduced are
still in use, notably the spirits of ether, or "Hoffman's anodyne."


Besides Hoffman's system of medicine, there were numerous others during
the eighteenth century, most of which are of no importance whatever;
but three, at least, that came into existence and disappeared during the
century are worthy of fuller notice. One of these, the Animists, had for
its chief exponent Georg Ernst Stahl of "phlogiston" fame; another, the
Vitalists, was championed by Paul Joseph Barthez (1734-1806); and the
third was the Organicists. This last, while agreeing with the other
two that vital activity cannot be explained by the laws of physics
and chemistry, differed in not believing that life "was due to some
spiritual entity," but rather to the structure of the body itself.

The Animists taught that the soul performed functions of ordinary life
in man, while the life of lower animals was controlled by ordinary
mechanical principles. Stahl supported this theory ardently, sometimes
violently, at times declaring that there were "no longer any doctors,
only mechanics and chemists." He denied that chemistry had anything to
do with medicine, and, in the main, discarded anatomy as useless to the
medical man. The soul, he thought, was the source of all vital movement;
and the immediate cause of death was not disease but the direct action
of the soul. When through some lesion, or because the machinery of the
body has become unworkable, as in old age, the soul leaves the body
and death is produced. The soul ordinarily selects the channels of the
circulation, and the contractile parts, as the route for influencing
the body. Hence in fever the pulse is quickened, due to the increased
activity of the soul, and convulsions and spasmodic movements in disease
are due, to the, same cause. Stagnation of the blood was supposed to
be a fertile cause of diseases, and such diseases were supposed to
arise mostly from "plethora"--an all-important element in Stahl's
therapeutics. By many this theory is regarded as an attempt on the
part of the pious Stahl to reconcile medicine and theology in a
way satisfactory to both physicians and theologians, but, like many
conciliatory attempts, it was violently opposed by both doctors and

A belief in such a theory would lead naturally to simplicity in
therapeutics, and in this respect at least Stahl was consistent. Since
the soul knew more about the body than any physician could know, Stahl
conceived that it would be a hinderance rather than a help for the
physician to interfere with complicated doses of medicine. As he
advanced in age this view of the administration of drugs grew upon him,
until after rejecting quinine, and finally opium, he at last used only
salt and water in treating his patients. From this last we may judge
that his "system," if not doing much good, was at least doing little

The theory of the Vitalists was closely allied to that of the Animists,
and its most important representative, Paul Joseph Barthez, was a
cultured and eager scientist. After an eventful and varied career as
physician, soldier, editor, lawyer, and philosopher in turn, he finally
returned to the field of medicine, was made consulting physician by
Napoleon in 1802, and died in Paris four years later.

The theory that he championed was based on the assumption that there was
a "vital principle," the nature of which was unknown, but which differed
from the thinking mind, and was the cause of the phenomena of life. This
"vital principle" differed from the soul, and was not exhibited in human
beings alone, but even in animals and plants. This force, or whatever it
might be called, was supposed to be present everywhere in the body, and
all diseases were the results of it.

The theory of the Organicists, like that of the Animists and Vitalists,
agreed with the other two that vital activity could not be explained by
the laws of physics and chemistry, but, unlike them, it held that it
was a part of the structure of the body itself. Naturally the practical
physicians were more attracted by this tangible doctrine than by vague
theories "which converted diseases into unknown derangements of some
equally unknown 'principle.'"

It is perhaps straining a point to include this brief description of
these three schools of medicine in the history of the progress of the
science. But, on the whole, they were negatively at least prominent
factors in directing true progress along its proper channel, showing
what courses were not to be pursued. Some one has said that science
usually stumbles into the right course only after stumbling into all
the wrong ones; and if this be only partially true, the wrong ones still
play a prominent if not a very creditable part. Thus the medical systems
of William Cullen (1710-1790), and John Brown (1735-1788), while doing
little towards the actual advancement of scientific medicine, played
so conspicuous a part in so wide a field that the "Brunonian system" at
least must be given some little attention.

According to Brown's theory, life, diseases, and methods of cure are
explained by the property of "excitability." All exciting powers were
supposed to be stimulating, the apparent debilitating effects of some
being due to a deficiency in the amount of stimulus. Thus "the whole
phenomena of life, health, as well as disease, were supposed to consist
of stimulus and nothing else." This theory created a great stir in the
medical world, and partisans and opponents sprang up everywhere. In
Italy it was enthusiastically supported; in England it was strongly
opposed; while in Scotland riots took place between the opposing
factions. Just why this system should have created any stir, either for
or against it, is not now apparent.

Like so many of the other "theorists" of his century, Brown's practical
conclusions deduced from his theory (or perhaps in spite of it) were
generally beneficial to medicine, and some of them extremely valuable in
the treatment of diseases. He first advocated the modern stimulant, or
"feeding treatment" of fevers, and first recognized the usefulness of
animal soups and beef-tea in certain diseases.


Just at the close of the century there came into prominence the school
of homoeopathy, which was destined to influence the practice of medicine
very materially and to outlive all the other eighteenth-century schools.
It was founded by Christian Samuel Friedrich Hahnemann (1755-1843), a
most remarkable man, who, after propounding a theory in his younger days
which was at least as reasonable as most of the existing theories, had
the misfortune to outlive his usefulness and lay his doctrine open to
ridicule by the unreasonable teachings of his dotage.

Hahnemann rejected all the teachings of morbid anatomy and pathology
as useless in practice, and propounded his famous "similia similibus
curantur"--that all diseases were to be cured by medicine which in
health produced symptoms dynamically similar to the disease under
treatment. If a certain medicine produced a headache when given to a
healthy person, then this medicine was indicated in case of headaches,
etc. At the present time such a theory seems crude enough, but in the
latter part of the eighteenth century almost any theory was as good as
the ones propounded by Animists, Vitalists, and other such schools. It
certainly had the very commendable feature of introducing simplicity
in the use of drugs in place of the complicated prescriptions then in
vogue. Had Hahnemann stopped at this point he could not have been
held up to the indefensible ridicule that was brought upon him, with
considerable justice, by his later theories. But he lived onto propound
his extraordinary theory of "potentiality"--that medicines gained
strength by being diluted--and his even more extraordinary theory
that all chronic diseases are caused either by the itch, syphilis, or
fig-wart disease, or are brought on by medicines.

At the time that his theory of potentialities was promulgated, the
medical world had gone mad in its administration of huge doses of
compound mixtures of drugs, and any reaction against this was surely
an improvement. In short, no medicine at all was much better than the
heaping doses used in common practice; and hence one advantage, at
least, of Hahnemann's methods. Stated briefly, his theory was that if a
tincture be reduced to one-fiftieth in strength, and this again reduced
to one-fiftieth, and this process repeated up to thirty such dilutions,
the potency of such a medicine will be increased by each dilution,
Hahnemann himself preferring the weakest, or, as he would call it, the
strongest dilution. The absurdity of such a theory is apparent when it
is understood that long before any drug has been raised to its thirtieth
dilution it has been so reduced in quantity that it cannot be weighed,
measured, or recognized as being present in the solution at all by
any means known to chemists. It is but just to modern followers of
homoeopathy to say that while most of them advocate small dosage, they
do not necessarily follow the teachings of Hahnemann in this respect,
believing that the theory of the dose "has nothing more to do with the
original law of cure than the psora (itch) theory has; and that it was
one of the later creations of Hahnemann's mind."

Hahnemann's theory that all chronic diseases are derived from either
itch, syphilis, or fig-wart disease is no longer advocated by his
followers, because it is so easily disproved, particularly in the case
of itch. Hahnemann taught that fully three-quarters of all diseases were
caused by "itch struck in," and yet it had been demonstrated long before
his day, and can be demonstrated any time, that itch is simply a local
skin disease caused by a small parasite.


All advances in science have a bearing, near or remote, on the welfare
of our race; but it remains to credit to the closing decade of the
eighteenth century a discovery which, in its power of direct and
immediate benefit to humanity, surpasses any other discovery of this or
any previous epoch. Needless to say, I refer to Jenner's discovery
of the method of preventing smallpox by inoculation with the virus of
cow-pox. It detracts nothing from the merit of this discovery to say
that the preventive power of accidental inoculation had long been
rumored among the peasantry of England. Such vague, unavailing
half-knowledge is often the forerunner of fruitful discovery.

To all intents and purposes Jenner's discovery was original and unique.
Nor, considered as a perfect method, was it in any sense an accident. It
was a triumph of experimental science. The discoverer was no novice in
scientific investigation, but a trained observer, who had served a long
apprenticeship in scientific observation under no less a scientist than
the celebrated John Hunter. At the age of twenty-one Jenner had gone to
London to pursue his medical studies, and soon after he proved himself
so worthy a pupil that for two years he remained a member of Hunter's
household as his favorite pupil. His taste for science and natural
history soon attracted the attention of Sir Joseph Banks, who intrusted
him with the preparation of the zoological specimens brought back by
Captain Cook's expedition in 1771. He performed this task so well that
he was offered the position of naturalist to the second expedition, but
declined it, preferring to take up the practice of his profession in his
native town of Berkeley.

His many accomplishments and genial personality soon made him a favorite
both as a physician and in society. He was a good singer, a fair
violinist and flute-player, and a very successful writer of prose and
verse. But with all his professional and social duties he still kept up
his scientific investigations, among other things making some careful
observations on the hibernation of hedgehogs at the instigation of
Hunter, the results of which were laid before the Royal Society. He also
made quite extensive investigations as to the geological formations and
fossils found in his neighborhood.

Even during his student days with Hunter he had been much interested in
the belief, current in the rural districts of Gloucestershire, of the
antagonism between cow-pox and small-pox, a person having suffered
from cow-pox being immuned to small-pox. At various times Jenner had
mentioned the subject to Hunter, and he was constantly making inquiries
of his fellow-practitioners as to their observations and opinions on the
subject. Hunter was too fully engrossed in other pursuits to give the
matter much serious attention, however, and Jenner's brothers of the
profession gave scant credence to the rumors, although such rumors were
common enough.

At this time the practice of inoculation for preventing small-pox, or
rather averting the severer forms of the disease, was widely practised.
It was customary, when there was a mild case of the disease, to take
some of the virus from the patient and inoculate persons who had never
had the disease, producing a similar attack in them. Unfortunately there
were many objections to this practice. The inoculated patient frequently
developed a virulent form of the disease and died; or if he recovered,
even after a mild attack, he was likely to be "pitted" and disfigured.
But, perhaps worst of all, a patient so inoculated became the source of
infection to others, and it sometimes happened that disastrous epidemics
were thus brought about. The case was a most perplexing one, for the
awful scourge of small-pox hung perpetually over the head of every
person who had not already suffered and recovered from it. The practice
of inoculation was introduced into England by Lady Mary Wortley Montague
(1690-1762), who had seen it practised in the East, and who announced
her intention of "introducing it into England in spite of the doctors."

From the fact that certain persons, usually milkmaids, who had suffered
from cow-pox seemed to be immuned to small-pox, it would seem a very
simple process of deduction to discover that cow-pox inoculation was the
solution of the problem of preventing the disease. But there was another
form of disease which, while closely resembling cow-pox and quite
generally confounded with it, did not produce immunity. The confusion of
these two forms of the disease had constantly misled investigations as
to the possibility of either of them immunizing against smallpox, and
the confusion of these two diseases for a time led Jenner to question
the possibility of doing so. After careful investigations, however, he
reached the conclusion that there was a difference in the effects of the
two diseases, only one of which produced immunity from small-pox.

"There is a disease to which the horse, from his state of domestication,
is frequently subject," wrote Jenner, in his famous paper on
vaccination. "The farriers call it the grease. It is an inflammation and
swelling in the heel, accompanied at its commencement with small cracks
or fissures, from which issues a limpid fluid possessing properties of a
very peculiar kind. This fluid seems capable of generating a disease
in the human body (after it has undergone the modification I shall
presently speak of) which bears so strong a resemblance to small-pox
that I think it highly probable it may be the source of that disease.

"In this dairy country a great number of cows are kept, and the office
of milking is performed indiscriminately by men and maid servants. One
of the former having been appointed to apply dressings to the heels of
a horse affected with the malady I have mentioned, and not paying due
attention to cleanliness, incautiously bears his part in milking the
cows with some particles of the infectious matter adhering to his
fingers. When this is the case it frequently happens that a disease is
communicated to the cows, and from the cows to the dairy-maids, which
spreads through the farm until most of the cattle and domestics feel its
unpleasant consequences. This disease has obtained the name of Cow-Pox.
It appears on the nipples of the cows in the form of irregular pustules.
At their first appearance they are commonly of a palish blue, or rather
of a color somewhat approaching to livid, and are surrounded by an
inflammation. These pustules, unless a timely remedy be applied,
frequently degenerate into phagedenic ulcers, which prove extremely
troublesome. The animals become indisposed, and the secretion of milk is
much lessened. Inflamed spots now begin to appear on different parts
of the hands of the domestics employed in milking, and sometimes on the
wrists, which run on to suppuration, first assuming the appearance of
the small vesications produced by a burn. Most commonly they appear
about the joints of the fingers and at their extremities; but whatever
parts are affected, if the situation will admit the superficial
suppurations put on a circular form with their edges more elevated than
their centre and of a color distinctly approaching to blue. Absorption
takes place, and tumors appear in each axilla. The system becomes
affected, the pulse is quickened; shiverings, succeeded by heat, general
lassitude, and pains about the loins and limbs, with vomiting, come on.
The head is painful, and the patient is now and then even affected
with delirium. These symptoms, varying in their degrees of violence,
generally continue from one day to three or four, leaving ulcerated
sores about the hands which, from the sensibility of the parts, are very
troublesome and commonly heal slowly, frequently becoming phagedenic,
like those from which they sprang. During the progress of the disease
the lips, nostrils, eyelids, and other parts of the body are sometimes
affected with sores; but these evidently arise from their being
heedlessly rubbed or scratched by the patient's infected fingers. No
eruptions on the skin have followed the decline of the feverish symptoms
in any instance that has come under my inspection, one only excepted,
and in this case a very few appeared on the arms: they were very
minute, of a vivid red color, and soon died away without advancing to
maturation, so that I cannot determine whether they had any connection
with the preceding symptoms.

"Thus the disease makes its progress from the horse (as I conceive) to
the nipple of the cow, and from the cow to the human subject.

"Morbid matter of various kinds, when absorbed into the system, may
produce effects in some degree similar; but what renders the cow-pox
virus so extremely singular is that the person that has been thus
affected is forever after secure from the infection of small-pox,
neither exposure to the variolous effluvia nor the insertion of the
matter into the skin producing this distemper."(2)

In 1796 Jenner made his first inoculation with cowpox matter, and two
months later the same subject was inoculated with small-pox matter. But,
as Jenner had predicted, no attack of small-pox followed. Although fully
convinced by this experiment that the case was conclusively proven, he
continued his investigations, waiting two years before publishing his
discovery. Then, fortified by indisputable proofs, he gave it to the
world. The immediate effects of his announcement have probably never
been equalled in the history of scientific discovery, unless, perhaps,
in the single instance of the discovery of anaesthesia. In Geneva and
Holland clergymen advocated the practice of vaccination from their
pulpits; in some of the Latin countries religious processions were
formed for receiving vaccination; Jenner's birthday was celebrated as
a feast in Germany; and the first child vaccinated in Russia was named
"Vaccinov" and educated at public expense. In six years the discovery
had penetrated to the most remote corners of civilization; it had even
reached some savage nations. And in a few years small-pox had fallen
from the position of the most dreaded of all diseases to that of being
practically the only disease for which a sure and easy preventive was

Honors were showered upon Jenner from the Old and the New World, and
even Napoleon, the bitter hater of the English, was among the others who
honored his name. On one occasion Jenner applied to the Emperor for the
release of certain Englishmen detained in France. The petition was about
to be rejected when the name of the petitioner was mentioned. "Ah," said
Napoleon, "we can refuse nothing to that name!"

It is difficult for us of to-day clearly to conceive the greatness of
Jenner's triumph, for we can only vaguely realize what a ruthless and
ever-present scourge smallpox had been to all previous generations of
men since history began. Despite all efforts to check it by medication
and by direct inoculation, it swept now and then over the earth as an
all-devastating pestilence, and year by year it claimed one-tenth of
all the beings in Christendom by death as its average quota of victims.
"From small-pox and love but few remain free," ran the old saw. A pitted
face was almost as much a matter of course a hundred years ago as a
smooth one is to-day.

Little wonder, then, that the world gave eager acceptance to Jenner's
discovery. No urging was needed to induce the majority to give it trial;
passengers on a burning ship do not hold aloof from the life-boats. Rich
and poor, high and low, sought succor in vaccination and blessed the
name of their deliverer. Of all the great names that were before the
world in the closing days of the century, there was perhaps no other one
at once so widely known and so uniformly reverenced as that of the great
English physician Edward Jenner. Surely there was no other one that
should be recalled with greater gratitude by posterity.



Although Napoleon Bonaparte, First Consul, was not lacking in
self-appreciation, he probably did not realize that in selecting a
physician for his own needs he was markedly influencing the progress
of medical science as a whole. Yet so strangely are cause and effect
adjusted in human affairs that this simple act of the First Consul had
that very unexpected effect. For the man chosen was the envoy of a new
method in medical practice, and the fame which came to him through being
physician to the First Consul, and subsequently to the Emperor, enabled
him to promulgate the method in a way otherwise impracticable. Hence the
indirect but telling value to medical science of Napoleon's selection.

The physician in question was Jean Nicolas de Corvisart. His novel
method was nothing more startling than the now-familiar procedure of
tapping the chest of a patient to elicit sounds indicative of diseased
tissues within. Every one has seen this done commonly enough in our day,
but at the beginning of the century Corvisart, and perhaps some of his
pupils, were probably the only physicians in the world who resorted to
this simple and useful procedure. Hence Napoleon's surprise when, on
calling in Corvisart, after becoming somewhat dissatisfied with
his other physicians Pinel and Portal, his physical condition was
interrogated in this strange manner. With characteristic shrewdness
Bonaparte saw the utility of the method, and the physician who thus
attempted to substitute scientific method for guess-work in the
diagnosis of disease at once found favor in his eyes and was installed
as his regular medical adviser.

For fifteen years before this Corvisart had practised percussion, as
the chest-tapping method is called, without succeeding in convincing the
profession of its value. The method itself, it should be added, had not
originated with Corvisart, nor did the French physician for a moment
claim it as his own. The true originator of the practice was the German
physician Avenbrugger, who published a book about it as early as 1761.
This book had even been translated into French, then the language of
international communication everywhere, by Roziere de la Chassagne, of
Montpellier, in 1770; but no one other than Corvisart appears to
have paid any attention to either original or translation. It was far
otherwise, however, when Corvisart translated Avenbrugger's work anew,
with important additions of his own, in 1808.

"I know very well how little reputation is allotted to translator and
commentators," writes Corvisart, "and I might easily have elevated
myself to the rank of an author if I had elaborated anew the doctrine
of Avenbrugger and published an independent work on percussion. In this
way, however, I should have sacrificed the name of Avenbrugger to my own
vanity, a thing which I am unwilling to do. It is he, and the beautiful
invention which of right belongs to him, that I desire to recall to

By this time a reaction had set in against the metaphysical methods in
medicine that had previously been so alluring; the scientific spirit of
the time was making itself felt in medical practice; and this, combined
with Corvisart's fame, brought the method of percussion into immediate
and well-deserved popularity. Thus was laid the foundation for
the method of so-called physical diagnosis, which is one of the
corner-stones of modern medicine.

The method of physical diagnosis as practised in our day was by no means
completed, however, with the work of Corvisart. Percussion alone tells
much less than half the story that may be elicited from the organs of
the chest by proper interrogation. The remainder of the story can
only be learned by applying the ear itself to the chest, directly or
indirectly. Simple as this seems, no one thought of practising it for
some years after Corvisart had shown the value of percussion.

Then, in 1815, another Paris physician, Rene Theophile Hyacinthe
Laennec, discovered, almost by accident, that the sound of the
heart-beat could be heard surprisingly through a cylinder of paper held
to the ear and against the patient's chest. Acting on the hint thus
received, Laennec substituted a hollow cylinder of wood for the paper,
and found himself provided with an instrument through which not merely
heart sounds but murmurs of the lungs in respiration could be heard with
almost startling distinctness.

The possibility of associating the varying chest sounds with diseased
conditions of the organs within appealed to the fertile mind of Laennec
as opening new vistas in therapeutics, which he determined to enter to
the fullest extent practicable. His connection with the hospitals of
Paris gave him full opportunity in this direction, and his labors of
the next few years served not merely to establish the value of the new
method as an aid to diagnosis, but laid the foundation also for the
science of morbid anatomy. In 1819 Laennec published the results of his
labors in a work called Traite d'Auscultation Mediate,(2) a work
which forms one of the landmarks of scientific medicine. By mediate
auscultation is meant, of course, the interrogation of the chest with
the aid of the little instrument already referred to, an instrument
which its originator thought hardly worth naming until various barbarous
appellations were applied to it by others, after which Laennec decided
to call it the stethoscope, a name which it has ever since retained.

In subsequent years the form of the stethoscope, as usually employed,
was modified and its value augmented by a binauricular attachment,
and in very recent years a further improvement has been made through
application of the principle of the telephone; but the essentials of
auscultation with the stethoscope were established in much detail by
Laennec, and the honor must always be his of thus taking one of the
longest single steps by which practical medicine has in our century
acquired the right to be considered a rational science. Laennec's
efforts cost him his life, for he died in 1826 of a lung disease
acquired in the course of his hospital practice; but even before this
his fame was universal, and the value of his method had been recognized
all over the world. Not long after, in 1828, yet another French
physician, Piorry, perfected the method of percussion by introducing
the custom of tapping, not the chest directly, but the finger or a small
metal or hard-rubber plate held against the chest-mediate percussion, in
short. This perfected the methods of physical diagnosis of diseases of
the chest in all essentials; and from that day till this percussion
and auscultation have held an unquestioned place in the regular
armamentarium of the physician.

Coupled with the new method of physical diagnosis in the effort to
substitute knowledge for guess-work came the studies of the experimental
physiologists--in particular, Marshall Hall in England and Francois
Magendie in France; and the joint efforts of these various workers
led presently to the abandonment of those severe and often irrational
depletive methods--blood-letting and the like--that had previously
dominated medical practice. To this end also the "statistical method,"
introduced by Louis and his followers, largely contributed; and by the
close of the first third of our century the idea was gaining ground that
the province of therapeutics is to aid nature in combating disease, and
that this may often be accomplished better by simple means than by
the heroic measures hitherto thought necessary. In a word, scientific
empiricism was beginning to gain a hearing in medicine as against the
metaphysical preconceptions of the earlier generations.


I have just adverted to the fact that Napoleon Bonaparte, as First
Consul and as Emperor, was the victim of a malady which caused him to
seek the advice of the most distinguished physicians of Paris. It is a
little shocking to modern sensibilities to read that these physicians,
except Corvisart, diagnosed the distinguished patient's malady as "gale
repercutee"--that is to say, in idiomatic English, the itch "struck in."
It is hardly necessary to say that no physician of today would make
so inconsiderate a diagnosis in the case of a royal patient. If by
any chance a distinguished patient were afflicted with the itch, the
sagacious physician would carefully hide the fact behind circumlocutions
and proceed to eradicate the disease with all despatch. That the
physicians of Napoleon did otherwise is evidence that at the beginning
of the century the disease in question enjoyed a very different status.
At that time itch, instead of being a most plebeian malady, was, so to
say, a court disease. It enjoyed a circulation, in high circles and in
low, that modern therapeutics has quite denied it; and the physicians
of the time gave it a fictitious added importance by ascribing to its
influence the existence of almost any obscure malady that came under
their observation. Long after Napoleon's time gale continued to hold
this proud distinction. For example, the imaginative Dr. Hahnemann did
not hesitate to affirm, as a positive maxim, that three-fourths of all
the ills that flesh is heir to were in reality nothing but various forms
of "gale repercutee."

All of which goes to show how easy it may be for a masked pretender to
impose on credulous humanity, for nothing is more clearly established in
modern knowledge than the fact that "gale repercutee" was simply a name
to hide a profound ignorance; no such disease exists or ever did exist.
Gale itself is a sufficiently tangible reality, to be sure, but it is a
purely local disease of the skin, due to a perfectly definite cause,
and the dire internal conditions formerly ascribed to it have really no
causal connection with it whatever. This definite cause, as every one
nowadays knows, is nothing more or less than a microscopic insect which
has found lodgment on the skin, and has burrowed and made itself at home
there. Kill that insect and the disease is no more; hence it has come to
be an axiom with the modern physician that the itch is one of the three
or four diseases that he positively is able to cure, and that very
speedily. But it was far otherwise with the physicians of the first
third of our century, because to them the cause of the disease was an
absolute mystery.

It is true that here and there a physician had claimed to find an insect
lodged in the skin of a sufferer from itch, and two or three times the
claim had been made that this was the cause of the malady, but such
views were quite ignored by the general profession, and in 1833 it was
stated in an authoritative medical treatise that the "cause of gale is
absolutely unknown." But even at this time, as it curiously happened,
there were certain ignorant laymen who had attained to a bit of medical
knowledge that was withheld from the inner circles of the profession. As
the peasantry of England before Jenner had known of the curative value
of cow-pox over small-pox, so the peasant women of Poland had learned
that the annoying skin disease from which they suffered was caused by
an almost invisible insect, and, furthermore, had acquired the trick of
dislodging the pestiferous little creature with the point of a needle.
From them a youth of the country, F. Renucci by name, learned the open
secret. He conveyed it to Paris when he went there to study medicine,
and in 1834 demonstrated it to his master Alibert. This physician, at
first sceptical, soon was convinced, and gave out the discovery to the
medical world with an authority that led to early acceptance.

Now the importance of all this, in the present connection, is not at all
that it gave the clew to the method of cure of a single disease. What
makes the discovery epochal is the fact that it dropped a brand-new
idea into the medical ranks--an idea destined, in the long-run, to
prove itself a veritable bomb--the idea, namely, that a minute and quite
unsuspected animal parasite may be the cause of a well-known, widely
prevalent, and important human disease. Of course the full force of this
idea could only be appreciated in the light of later knowledge; but even
at the time of its coming it sufficed to give a great impetus to that
new medical knowledge, based on microscopical studies, which had but
recently been made accessible by the inventions of the lens-makers. The
new knowledge clarified one very turbid medical pool and pointed the way
to the clarification of many others.

Almost at the same time that the Polish medical student was
demonstrating the itch mite in Paris, it chanced, curiously enough,
that another medical student, this time an Englishman, made an analogous
discovery of perhaps even greater importance. Indeed, this English
discovery in its initial stages slightly antedated the other, for it
was in 1833 that the student in question, James Paget, interne in St.
Bartholomew's Hospital, London, while dissecting the muscular tissues of
a human subject, found little specks of extraneous matter, which,
when taken to the professor of comparative anatomy, Richard Owen, were
ascertained, with the aid of the microscope, to be the cocoon of a
minute and hitherto unknown insect. Owen named the insect Trichina
spiralis. After the discovery was published it transpired that similar
specks had been observed by several earlier investigators, but no one
had previously suspected or, at any rate, demonstrated their nature. Nor
was the full story of the trichina made out for a long time after Owen's
discovery. It was not till 1847 that the American anatomist Dr. Joseph
Leidy found the cysts of trichina in the tissues of pork; and another
decade or so elapsed after that before German workers, chief among whom
were Leuckart, Virchow, and Zenker, proved that the parasite gets into
the human system through ingestion of infected pork, and that it causes
a definite set of symptoms of disease which hitherto had been mistaken
for rheumatism, typhoid fever, and other maladies. Then the medical
world was agog for a time over the subject of trichinosis; government
inspection of pork was established in some parts of Germany; American
pork was excluded altogether from France; and the whole subject thus
came prominently to public attention. But important as the trichina
parasite proved on its own account in the end, its greatest importance,
after all, was in the share it played in directing attention at the
time of its discovery in 1833 to the subject of microscopic parasites in

The decade that followed that discovery was a time of great activity in
the study of microscopic organisms and microscopic tissues, and such
men as Ehrenberg and Henle and Bory Saint-Vincent and Kolliker and
Rokitansky and Remak and Dujardin were widening the bounds of knowledge
of this new subject with details that cannot be more than referred to
here. But the crowning achievement of the period in this direction was
the discovery made by the German, J. L. Schoenlein, in 1839, that a very
common and most distressing disease of the scalp, known as favus,
is really due to the presence and growth on the scalp of a vegetable
organism of microscopic size. Thus it was made clear that not merely
animal but also vegetable organisms of obscure, microscopic species have
causal relations to the diseases with which mankind is afflicted. This
knowledge of the parasites was another long step in the direction of
scientific medical knowledge; but the heights to which this knowledge
led were not to be scaled, or even recognized, until another generation
of workers had entered the field.


Meantime, in quite another field of medicine, events were developing
which led presently to a revelation of greater immediate importance to
humanity than any other discovery that had come in the century,
perhaps in any field of science whatever. This was the discovery of
the pain-dispelling power of the vapor of sulphuric ether inhaled by a
patient undergoing a surgical operation. This discovery came solely out
of America, and it stands curiously isolated, since apparently no minds
in any other country were trending towards it even vaguely. Davy, in
England, had indeed originated the method of medication by inhalation,
and earned out some most interesting experiments fifty years earlier,
and it was doubtless his experiments with nitrous oxide gas that gave
the clew to one of the American investigators; but this was the sole
contribution of preceding generations to the subject, and since the
beginning of the century, when Davy turned his attention to other
matters, no one had made the slightest advance along the same line until
an American dentist renewed the investigation.

In view of the sequel, Davy's experiments merit full attention. Here is
his own account of them, as written in 1799:

"Immediately after a journey of one hundred and twenty-six miles,
in which I had no sleep the preceding night, being much exhausted, I
respired seven quarts of nitrous oxide gas for near three minutes. It
produced the usual pleasurable effects and slight muscular motion. I
continued exhilarated for some minutes afterwards, but in half an hour
found myself neither more nor less exhausted than before the experiment.
I had a great propensity to sleep.

"To ascertain with certainty whether the more extensive action of
nitrous oxide compatible with life was capable of producing debility, I
resolved to breathe the gas for such a time, and in such quantities,
as to produce excitement equal in duration and superior in intensity to
that occasioned by high intoxication from opium or alcohol.

"To habituate myself to the excitement, and to carry it on gradually,
on December 26th I was enclosed in an air-tight breathing-box, of the
capacity of about nine and one-half cubic feet, in the presence of Dr.
Kinglake. After I had taken a situation in which I could by means of a
curved thermometer inserted under the arm, and a stop-watch, ascertain
the alterations in my pulse and animal heat, twenty quarts of nitrous
oxide were thrown into the box.

"For three minutes I experienced no alteration in my sensations, though
immediately after the introduction of the nitrous oxide the smell and
taste of it were very evident. In four minutes I began to feel a slight
glow in the cheeks and a generally diffused warmth over the chest,
though the temperature of the box was not quite 50 degrees.... In
twenty-five minutes the animal heat was 100 degrees, pulse 124. In
thirty minutes twenty quarts more of gas were introduced.

"My sensations were now pleasant; I had a generally diffused warmth
without the slightest moisture of the skin, a sense of exhilaration
similar to that produced by a small dose of wine, and a disposition to
muscular motion and to merriment.

"In three-quarters of an hour the pulse was 104 and the animal heat not
99.5 degrees, the temperature of the chamber 64 degrees. The pleasurable
feelings continued to increase, the pulse became fuller and slower, till
in about an hour it was 88, when the animal heat was 99 degrees. Twenty
quarts more of air were admitted. I had now a great disposition to
laugh, luminous points seemed frequently to pass before my eyes, my
hearing was certainly more acute, and I felt a pleasant lightness and
power of exertion in my muscles. In a short time the symptoms became
stationary; breathing was rather oppressed, and on account of the great
desire for action rest was painful.

"I now came out of the box, having been in precisely an hour and a
quarter. The moment after I began to respire twenty quarts of unmingled
nitrous oxide. A thrilling extending from the chest to the extremities
was almost immediately produced. I felt a sense of tangible extension
highly pleasurable in every limb; my visible impressions were dazzling
and apparently magnified, I heard distinctly every sound in the room,
and was perfectly aware of my situation. By degrees, as the pleasurable
sensations increased, I lost all connection with external things;
trains of vivid visible images rapidly passed through my mind and
were connected with words in such a manner as to produce perceptions
perfectly novel.

"I existed in a world of newly connected and newly modified ideas. I
theorized; I imagined that I made discoveries. When I was awakened from
this semi-delirious trance by Dr. Kinglake, who took the bag from my
mouth, indignation and pride were the first feelings produced by the
sight of persons about me. My emotions were enthusiastic and sublime;
and for a minute I walked about the room perfectly regardless of what
was said to me. As I recovered my former state of mind, I felt an
inclination to communicate the discoveries I had made during the
experiment. I endeavored to recall the ideas--they were feeble and
indistinct; one collection of terms, however, presented itself, and,
with most intense belief and prophetic manner, I exclaimed to Dr.
Kinglake, 'Nothing exists but thoughts!--the universe is composed of
impressions, ideas, pleasures, and pains.' "(3)

From this account we see that Davy has anaesthetized himself to a point
where consciousness of surroundings was lost, but not past the stage
of exhilaration. Had Dr. Kinglake allowed the inhaling-bag to remain in
Davy's mouth for a few moments longer complete insensibility would have
followed. As it was, Davy appears to have realized that sensibility was
dulled, for he adds this illuminative suggestion: "As nitrous oxide in
its extensive operation appears capable of destroying physical pain, it
may probably be used with advantage during surgical operations in which
no great effusion of blood takes place."(4)

Unfortunately no one took advantage of this suggestion at the time,
and Davy himself became interested in other fields of science and never
returned to his physiological studies, thus barely missing one of the
greatest discoveries in the entire field of science. In the generation
that followed no one seems to have thought of putting Davy's suggestion
to the test, and the surgeons of Europe had acknowledged with one accord
that all hope of finding a means to render operations painless must be
utterly abandoned--that the surgeon's knife must ever remain a synonym
for slow and indescribable torture. By an odd coincidence it chanced
that Sir Benjamin Brodie, the acknowledged leader of English surgeons,
had publicly expressed this as his deliberate though regretted opinion
at a time when the quest which he considered futile had already led to
the most brilliant success in America, and while the announcement of
the discovery, which then had no transatlantic cable to convey it, was
actually on its way to the Old World.

The American dentist just referred to, who was, with one exception to
be noted presently, the first man in the world to conceive that the
administration of a definite drug might render a surgical operation
painless and to give the belief application was Dr. Horace Wells, of
Hartford, Connecticut. The drug with which he experimented was nitrous
oxide--the same that Davy had used; the operation that he rendered
painless was no more important than the extraction of a tooth--yet it
sufficed to mark a principle; the year of the experiment was 1844.

The experiments of Dr. Wells, however, though important, were not
sufficiently demonstrative to bring the matter prominently to the
attention of the medical world. The drug with which he experimented
proved not always reliable, and he himself seems ultimately to have
given the matter up, or at least to have relaxed his efforts.
But meantime a friend, to whom he had communicated his belief and
expectations, took the matter up, and with unremitting zeal carried
forward experiments that were destined to lead to more tangible results.
This friend was another dentist, Dr. W. T. G. Morton, of Boston, then a
young man full of youthful energy and enthusiasm. He seems to have
felt that the drug with which Wells had experimented was not the
most practicable one for the purpose, and so for several months
he experimented with other allied drugs, until finally he hit upon
sulphuric ether, and with this was able to make experiments upon
animals, and then upon patients in the dental chair, that seemed to him
absolutely demonstrative.

Full of eager enthusiasm, and absolutely confident of his results, he at
once went to Dr. J. C. Warren, one of the foremost surgeons of Boston,
and asked permission to test his discovery decisively on one of the
patients at the Boston Hospital during a severe operation. The request
was granted; the test was made on October 16, 1846, in the presence of
several of the foremost surgeons of the city and of a body of medical
students. The patient slept quietly while the surgeon's knife was plied,
and awoke to astonished comprehension that the ordeal was over. The
impossible, the miraculous, had been accomplished.(5)

Swiftly as steam could carry it--slowly enough we should think it
to-day--the news was heralded to all the world. It was received in
Europe with incredulity, which vanished before repeated experiments.
Surgeons were loath to believe that ether, a drug that had long held
a place in the subordinate armamentarium of the physician, could
accomplish such a miracle. But scepticism vanished before the tests
which any surgeon might make, and which surgeons all over the world did
make within the next few weeks. Then there came a lingering outcry from
a few surgeons, notably some of the Parisians, that the shock of pain
was beneficial to the patient, hence that anaesthesia--as Dr. Oliver
Wendell Holmes had christened the new method--was a procedure not to
be advised. Then, too, there came a hue-and-cry from many a pulpit that
pain was God-given, and hence, on moral grounds, to be clung to rather
than renounced. But the outcry of the antediluvians of both hospital
and pulpit quickly received its quietus; for soon it was clear that the
patient who did not suffer the shock of pain during an operation rallied
better than the one who did so suffer, while all humanity outside the
pulpit cried shame to the spirit that would doom mankind to suffer
needless agony. And so within a few months after that initial operation
at the Boston Hospital in 1846, ether had made good its conquest of
pain throughout the civilized world. Only by the most active use of the
imagination can we of this present day realize the full meaning of that

It remains to be added that in the subsequent bickerings over the
discovery--such bickerings as follow every great advance--two other
names came into prominent notice as sharers in the glory of the new
method. Both these were Americans--the one, Dr. Charles T. Jackson, of
Boston; the other, Dr. Crawford W. Long, of Alabama. As to Dr. Jackson,
it is sufficient to say that he seems to have had some vague inkling
of the peculiar properties of ether before Morton's discovery. He even
suggested the use of this drug to Morton, not knowing that Morton had
already tried it; but this is the full measure of his association with
the discovery. Hence it is clear that Jackson's claim to equal share
with Morton in the discovery was unwarranted, not to say absurd.

Dr. Long's association with the matter was far different and altogether
honorable. By one of those coincidences so common in the history
of discovery, he was experimenting with ether as a pain-destroyer
simultaneously with Morton, though neither so much as knew of the
existence of the other. While a medical student he had once inhaled
ether for the intoxicant effects, as other medical students were wont to
do, and when partially under influence of the drug he had noticed that a
chance blow to his shins was painless. This gave him the idea that ether
might be used in surgical operations; and in subsequent years, in the
course of his practice in a small Georgia town, he put the idea into
successful execution. There appears to be no doubt whatever that he
performed successful minor operations under ether some two or three
years before Morton's final demonstration; hence that the merit of first
using the drug, or indeed any drug, in this way belongs to him. But,
unfortunately, Dr. Long did not quite trust the evidence of his own
experiments. Just at that time the medical journals were full of
accounts of experiments in which painless operations were said to be
performed through practice of hypnotism, and Dr. Long feared that his
own success might be due to an incidental hypnotic influence rather than
to the drug. Hence he delayed announcing his apparent discovery until
he should have opportunity for further tests--and opportunities did not
come every day to the country practitioner. And while he waited, Morton
anticipated him, and the discovery was made known to the world without
his aid. It was a true scientific caution that actuated Dr. Long to this
delay, but the caution cost him the credit, which might otherwise have
been his, of giving to the world one of the greatest blessings--dare we
not, perhaps, say the very greatest?--that science has ever conferred
upon humanity.

A few months after the use of ether became general, the Scotch surgeon
Sir J. Y. Simpson(6) discovered that another drug, chloroform, could be
administered with similar effects; that it would, indeed, in many cases
produce anaesthesia more advantageously even than ether. From that day
till this surgeons have been more or less divided in opinion as to
the relative merits of the two drugs; but this fact, of course, has no
bearing whatever upon the merit of the first discovery of the method of
anaesthesia. Even had some other drug subsequently quite banished ether,
the honor of the discovery of the beneficent method of anaesthesia would
have been in no wise invalidated. And despite all cavillings, it is
unequivocally established that the man who gave that method to the world
was William T. G. Morton.


The discovery of the anaesthetic power of drugs was destined presently,
in addition to its direct beneficences, to aid greatly in the progress
of scientific medicine, by facilitating those experimental studies
of animals from which, before the day of anaesthesia, many humane
physicians were withheld, and which in recent years have led to
discoveries of such inestimable value to humanity. But for the moment
this possibility was quite overshadowed by the direct benefits of
anaesthesia, and the long strides that were taken in scientific medicine
during the first fifteen years after Morton's discovery were mainly
independent of such aid. These steps were taken, indeed, in a field
that at first glance might seem to have a very slight connection with
medicine. Moreover, the chief worker in the field was not himself a
physician. He was a chemist, and the work in which he was now engaged
was the study of alcoholic fermentation in vinous liquors. Yet these
studies paved the way for the most important advances that medicine has
made in any century towards the plane of true science; and to this man
more than to any other single individual--it might almost be said more
than to all other individuals--was due this wonderful advance. It is
almost superfluous to add that the name of this marvellous chemist was
Louis Pasteur.

The studies of fermentation which Pasteur entered upon in 1854 were
aimed at the solution of a controversy that had been waging in the
scientific world with varying degrees of activity for a quarter of a
century. Back in the thirties, in the day of the early enthusiasm over
the perfected microscope, there had arisen a new interest in the minute
forms of life which Leeuwenhoek and some of the other early workers with
the lens had first described, and which now were shown to be of almost
universal prevalence. These minute organisms had been studied more or
less by a host of observers, but in particular by the Frenchman Cagniard
Latour and the German of cell-theory fame, Theodor Schwann. These men,
working independently, had reached the conclusion, about 1837, that
the micro-organisms play a vastly more important role in the economy
of nature than any one previously had supposed. They held, for example,
that the minute specks which largely make up the substance of yeast are
living vegetable organisms, and that the growth of these organisms is
the cause of the important and familiar process of fermentation. They
even came to hold, at least tentatively, the opinion that the somewhat
similar micro-organisms to be found in all putrefying matter, animal or
vegetable, had a causal relation to the process of putrefaction.

This view, particularly as to the nature of putrefaction, was expressed
even more outspokenly a little later by the French botanist Turpin.
Views so supported naturally gained a following; it was equally natural
that so radical an innovation should be antagonized. In this case it
chanced that one of the most dominating scientific minds of the time,
that of Liebig, took a firm and aggressive stand against the new
doctrine. In 1839 he promulgated his famous doctrine of fermentation,
in which he stood out firmly against any "vitalistic" explanation of the
phenomena, alleging that the presence of micro-organisms in fermenting
and putrefying substances was merely incidental, and in no sense causal.
This opinion of the great German chemist was in a measure substantiated
by experiments of his compatriot Helmholtz, whose earlier experiments
confirmed, but later ones contradicted, the observations of Schwann, and
this combined authority gave the vitalistic conception a blow from which
it had not rallied at the time when Pasteur entered the field. Indeed,
it was currently regarded as settled that the early students of the
subject had vastly over-estimated the importance of micro-organisms.

And so it came as a new revelation to the generality of scientists
of the time, when, in 1857 and the succeeding half-decade, Pasteur
published the results of his researches, in which the question had been
put to a series of altogether new tests, and brought to unequivocal

He proved that the micro-organisms do all that his most imaginative
predecessors had suspected, and more. Without them, he proved, there
would be no fermentation, no putrefaction--no decay of any tissues,
except by the slow process of oxidation. It is the microscopic
yeast-plant which, by seizing on certain atoms of the molecule,
liberates the remaining atoms in the form of carbonic-acid and alcohol,
thus effecting fermentation; it is another microscopic plant--a
bacterium, as Devaine had christened it--which in a similar way effects
the destruction of organic molecules, producing the condition which we
call putrefaction. Pasteur showed, to the amazement of biologists, that
there are certain forms of these bacteria which secure the oxygen which
all organic life requires, not from the air, but by breaking up unstable
molecules in which oxygen is combined; that putrefaction, in short, has
its foundation in the activities of these so-called anaerobic bacteria.

In a word, Pasteur showed that all the many familiar processes of the
decay of organic tissues are, in effect, forms of fermentation, and
would not take place at all except for the presence of the living
micro-organisms. A piece of meat, for example, suspended in an
atmosphere free from germs, will dry up gradually, without the slightest
sign of putrefaction, regardless of the temperature or other conditions
to which it may have been subjected. Let us witness one or two series of
these experiments as presented by Pasteur himself in one of his numerous
papers before the Academy of Sciences.


"In the course of the discussion which took place before the Academy
upon the subject of the generation of ferments properly so-called, there
was a good deal said about that of wine, the oldest fermentation known.
On this account I decided to disprove the theory of M. Fremy by a
decisive experiment bearing solely upon the juice of grapes.

"I prepared forty flasks of a capacity of from two hundred and fifty to
three hundred cubic centimetres and filled them half full with filtered
grape-must, perfectly clear, and which, as is the case of all acidulated
liquids that have been boiled for a few seconds, remains uncontaminated
although the curved neck of the flask containing them remain constantly
open during several months or years.

"In a small quantity of water I washed a part of a bunch of grapes, the
grapes and the stalks together, and the stalks separately. This
washing was easily done by means of a small badger's-hair brush. The
washing-water collected the dust upon the surface of the grapes and the
stalks, and it was easily shown under the microscope that this water
held in suspension a multitude of minute organisms closely resembling
either fungoid spores, or those of alcoholic Yeast, or those of
Mycoderma vini, etc. This being done, ten of the forty flasks were
preserved for reference; in ten of the remainder, through the straight
tube attached to each, some drops of the washing-water were introduced;
in a third series of ten flasks a few drops of the same liquid were
placed after it had been boiled; and, finally, in the ten remaining
flasks were placed some drops of grape-juice taken from the inside of a
perfect fruit. In order to carry out this experiment, the straight tube
of each flask was drawn out into a fine and firm point in the lamp, and
then curved. This fine and closed point was filed round near the end and
inserted into the grape while resting upon some hard substance. When
the point was felt to touch the support of the grape it was by a slight
pressure broken off at the point file mark. Then, if care had been taken
to create a slight vacuum in the flask, a drop of the juice of the grape
got into it, the filed point was withdrawn, and the aperture immediately
closed in the alcohol lamp. This decreased pressure of the atmosphere in
the flask was obtained by the following means: After warming the sides
of the flask either in the hands or in the lamp-flame, thus causing a
small quantity of air to be driven out of the end of the curved neck,
this end was closed in the lamp. After the flask was cooled, there was
a tendency to suck in the drop of grape-juice in the manner just

"The drop of grape-juice which enters into the flask by this suction
ordinarily remains in the curved part of the tube, so that to mix it
with the must it was necessary to incline the flask so as to bring
the must into contact with the juice and then replace the flask in its
normal position. The four series of comparative experiments produced the
following results:

"The first ten flasks containing the grape-must boiled in pure air did
not show the production of any organism. The grape-must could possibly
remain in them for an indefinite number of years. Those in the second
series, containing the water in which the grapes had been washed
separately and together, showed without exception an alcoholic
fermentation which in several cases began to appear at the end of
forty-eight hours when the experiment took place at ordinary summer
temperature. At the same time that the yeast appeared, in the form of
white traces, which little by little united themselves in the form of a
deposit on the sides of all the flasks, there were seen to form little
flakes of Mycellium, often as a single fungoid growth or in combination,
these fungoid growths being quite independent of the must or of any
alcoholic yeast. Often, also, the Mycoderma vini appeared after some
days upon the surface of the liquid. The Vibria and the lactic ferments
properly so called did not appear on account of the nature of the

"The third series of flasks, the washing-water in which had been
previously boiled, remained unchanged, as in the first series. Those of
the fourth series, in which was the juice of the interior of the grapes,
remained equally free from change, although I was not always able, on
account of the delicacy of the experiment, to eliminate every chance of
error. These experiments cannot leave the least doubt in the mind as to
the following facts:

"Grape-must, after heating, never ferments on contact with the air, when
the air has been deprived of the germs which it ordinarily holds in a
state of suspension.

"The boiled grape-must ferments when there is introduced into it a very
small quantity of water in which the surface of the grapes or their
stalks have been washed.

"The grape-must does not ferment when this washing-water has been boiled
and afterwards cooled.

"The grape-must does not ferment when there is added to it a small
quantity of the juice of the inside of the grape.

"The yeast, therefore, which causes the fermentation of the grapes in
the vintage-tub comes from the outside and not from the inside of the
grapes. Thus is destroyed the hypothesis of MM. Trecol and Fremy, who
surmised that the albuminous matter transformed itself into yeast
on account of the vital germs which were natural to it. With greater
reason, therefore, there is no longer any question of the theory of
Liebig of the transformation of albuminoid matter into ferments on
account of the oxidation."


"The method which I have just followed," Pasteur continues, "in order
to show that there exists a correlation between the diseases of beer and
certain microscopic organisms leaves no room for doubt, it seems to me,
in regard to the principles I am expounding.

"Every time that the microscope reveals in the leaven, and especially in
the active yeast, the production of organisms foreign to the alcoholic
yeast properly so called, the flavor of the beer leaves something to be
desired, much or little, according to the abundance and the character of
these little germs. Moreover, when a finished beer of good quality loses
after a time its agreeable flavor and becomes sour, it can be easily
shown that the alcoholic yeast deposited in the bottles or the casks,
although originally pure, at least in appearance, is found to be
contaminated gradually with these filiform or other ferments. All
this can be deduced from the facts already given, but some critics may
perhaps declare that these foreign ferments are the consequences of the
diseased condition, itself produced by unknown causes.

"Although this gratuitous hypothesis may be difficult to uphold, I will
endeavor to corroborate the preceding observations by a clearer method
of investigation. This consists in showing that the beer never has any
unpleasant taste in all cases when the alcoholic ferment properly so
called is not mixed with foreign ferments; that it is the same in
the case of wort, and that wort, liable to changes as it is, can be
preserved unaltered if it is kept from those microscopic parasites which
find in it a suitable nourishment and a field for growth.

"The employment of this second method has, moreover, the advantage of
proving with certainty the proposition that I advanced at first--namely,
that the germs of these organisms are derived from the dust of the
atmosphere, carried about and deposited upon all objects, or scattered
over the utensils and the materials used in a brewery-materials
naturally charged with microscopic germs, and which the various
operations in the store-rooms and the malt-house may multiply

"Let us take a glass flask with a long neck of from two hundred and
fifty to three hundred cubic centimetres capacity, and place in it some
wort, with or without hops, and then in the flame of a lamp draw out the
neck of the flask to a fine point, afterwards heating the liquid until
the steam comes out of the end of the neck. It can then be allowed to
cool without any other precautions; but for additional safety there
can be introduced into the little point a small wad of asbestos at the
moment that the flame is withdrawn from beneath the flask. Before thus
placing the asbestos it also can be passed through the flame, as well as
after it has been put into the end of the tube. The air which then first
re-enters the flask will thus come into contact with the heated glass
and the heated liquid, so as to destroy the vitality of any dust germs
that may exist in the air. The air itself will re-enter very gradually,
and slowly enough to enable any dust to be taken up by the drop of water
which the air forces up the curvature of the tube. Ultimately the tube
will be dry, but the re-entering of the air will be so slow that the
particles of dust will fall upon the sides of the tube. The experiments
show that with this kind of vessel, allowing free communication with the
air, and the dust not being allowed to enter, the dust will not enter
at all events for a period of ten or twelve years, which has been the
longest period devoted to these trials; and the liquid, if it were
naturally limpid, will not be in the least polluted neither on its
surface nor in its mass, although the outside of the flask may become
thickly coated with dust. This is a most irrefutable proof of the
impossibility of dust getting inside the flask.

"The wort thus prepared remains uncontaminated indefinitely, in spite
of its susceptibility to change when exposed to the air under conditions
which allow it to gather the dusty particles which float in the
atmosphere. It is the same in the case of urine, beef-tea, and
grape-must, and generally with all those putrefactable and fermentable
liquids which have the property when heated to boiling-point of
destroying the vitality of dust germs."(7)

There was nothing in these studies bearing directly upon the question
of animal diseases, yet before they were finished they had stimulated
progress in more than one field of pathology. At the very outset
they sufficed to start afresh the inquiry as to the role played by
micro-organisms in disease. In particular they led the French physician
Devaine to return to some interrupted studies which he had made ten
years before in reference to the animal disease called anthrax, or
splenic fever, a disease that cost the farmers of Europe millions of
francs annually through loss of sheep and cattle. In 1850 Devaine had
seen multitudes of bacteria in the blood of animals who had died of
anthrax, but he did not at that time think of them as having a causal
relation to the disease. Now, however, in 1863, stimulated by Pasteur's
new revelations regarding the power of bacteria, he returned to the
subject, and soon became convinced, through experiments by means of
inoculation, that the microscopic organisms he had discovered were the
veritable and the sole cause of the infectious disease anthrax.

The publication of this belief in 1863 aroused a furor of controversy.
That a microscopic vegetable could cause a virulent systemic disease
was an idea altogether too startling to be accepted in a day, and the
generality of biologists and physicians demanded more convincing proofs
than Devaine as yet was able to offer.

Naturally a host of other investigators all over the world entered the
field. Foremost among these was the German Dr. Robert Koch, who soon
corroborated all that Devaine had observed, and carried the experiments
further in the direction of the cultivation of successive generations of
the bacteria in artificial media, inoculations being made from such
pure cultures of the eighth generation, with the astonishing result that
animals thus inoculated succumbed to the disease.

Such experiments seem demonstrative, yet the world was unconvinced,
and in 1876, while the controversy was still at its height, Pasteur
was prevailed upon to take the matter in hand. The great chemist was
becoming more and more exclusively a biologist as the years passed, and
in recent years his famous studies of the silk-worm diseases, which he
proved due to bacterial infection, and of the question of spontaneous
generation, had given him unequalled resources in microscopical
technique. And so when, with the aid of his laboratory associates
Duclaux and Chamberland and Roux, he took up the mooted anthrax question
the scientific world awaited the issue with bated breath. And when, in
1877, Pasteur was ready to report on his studies of anthrax, he came
forward with such a wealth of demonstrative experiments--experiments
the rigid accuracy of which no one would for a moment think of
questioning--going to prove the bacterial origin of anthrax, that
scepticism was at last quieted for all time to come.

Henceforth no one could doubt that the contagious disease anthrax is due
exclusively to the introduction into an animal's system of a specific
germ--a microscopic plant--which develops there. And no logical mind
could have a reasonable doubt that what is proved true of one infectious
disease would some day be proved true also of other, perhaps of all,
forms of infectious maladies.

Hitherto the cause of contagion, by which certain maladies spread from
individual to individual, had been a total mystery, quite unillumined
by the vague terms "miasm," "humor," "virus," and the like cloaks of
ignorance. Here and there a prophet of science, as Schwann and Henle,
had guessed the secret; but guessing, in science, is far enough from
knowing. Now, for the first time, the world KNEW, and medicine had taken
another gigantic stride towards the heights of exact science.


Meantime, in a different though allied field of medicine there had
been a complementary growth that led to immediate results of even more
practical importance. I mean the theory and practice of antisepsis in
surgery. This advance, like the other, came as a direct outgrowth of
Pasteur's fermentation studies of alcoholic beverages, though not at
the hands of Pasteur himself. Struck by the boundless implications of
Pasteur's revelations regarding the bacteria, Dr. Joseph Lister (the
present Lord Lister), then of Glasgow, set about as early as 1860 to
make a wonderful application of these ideas. If putrefaction is always
due to bacterial development, he argued, this must apply as well to
living as to dead tissues; hence the putrefactive changes which occur
in wounds and after operations on the human subject, from which
blood-poisoning so often follows, might be absolutely prevented if the
injured surfaces could be kept free from access of the germs of decay.

In the hope of accomplishing this result, Lister began experimenting
with drugs that might kill the bacteria without injury to the patient,
and with means to prevent further access of germs once a wound was freed
from them. How well he succeeded all the world knows; how bitterly
he was antagonized for about a score of years, most of the world has
already forgotten. As early as 1867 Lister was able to publish results
pointing towards success in his great project; yet so incredulous were
surgeons in general that even some years later the leading surgeons
on the Continent had not so much as heard of his efforts. In 1870 the
soldiers of Paris died, as of old, of hospital gangrene; and when,
in 1871, the French surgeon Alphonse Guerin, stimulated by Pasteur's
studies, conceived the idea of dressing wounds with cotton in the hope
of keeping germs from entering them, he was quite unaware that a
British contemporary had preceded him by a full decade in this effort at
prevention and had made long strides towards complete success. Lister's
priority, however, and the superiority of his method, were freely
admitted by the French Academy of Sciences, which in 1881 officially
crowned his achievement, as the Royal Society of London had done the
year before.

By this time, to be sure, as everybody knows, Lister's new methods had
made their way everywhere, revolutionizing the practice of surgery and
practically banishing from the earth maladies that hitherto had been the
terror of the surgeon and the opprobrium of his art. And these bedside
studies, conducted in the end by thousands of men who had no knowledge
of microscopy, had a large share in establishing the general belief in
the causal relation that micro-organisms bear to disease, which by about
the year 1880 had taken possession of the medical world. But they did
more; they brought into equal prominence the idea that, the cause of
a diseased condition being known, it maybe possible as never before to
grapple with and eradicate that condition.


The controversy over spontaneous generation, which, thanks to Pasteur
and Tyndall, had just been brought to a termination, made it clear that
no bacterium need be feared where an antecedent bacterium had not
found lodgment; Listerism in surgery had now shown how much might be
accomplished towards preventing the access of germs to abraded surfaces
of the body and destroying those that already had found lodgment there.
As yet, however, there was no inkling of a way in which a corresponding
onslaught might be made upon those other germs which find their way into
the animal organism by way of the mouth and the nostrils, and which, as
was now clear, are the cause of those contagious diseases which, first
and last, claim so large a proportion of mankind for their victims.
How such means might be found now became the anxious thought of every
imaginative physician, of every working microbiologist.

As it happened, the world was not kept long in suspense. Almost before
the proposition had taken shape in the minds of the other leaders,
Pasteur had found a solution. Guided by the empirical success of Jenner,
he, like many others, had long practised inoculation experiments, and on
February 9, 1880, he announced to the French Academy of Sciences that he
had found a method of so reducing the virulence of a disease germ that
when introduced into the system of a susceptible animal it produced only
a mild form of the disease, which, however, sufficed to protect against
the usual virulent form exactly as vaccinia protects against small-pox.
The particular disease experimented with was that infectious malady of
poultry known familiarly as "chicken cholera." In October of the same
year Pasteur announced the method by which this "attenuation of the
virus," as he termed it, had been brought about--by cultivation of the
disease germs in artificial media, exposed to the air, and he did not
hesitate to assert his belief that the method would prove "susceptible
of generalization"--that is to say, of application to other diseases
than the particular one in question.

Within a few months he made good this prophecy, for in February,
1881, he announced to the Academy that with the aid, as before, of his
associates MM. Chamberland and Roux, he had produced an attenuated virus
of the anthrax microbe by the use of which, as he affirmed with great
confidence, he could protect sheep, and presumably cattle, against that
fatal malady. "In some recent publications," said Pasteur, "I announced
the first case of the attenuation of a virus by experimental methods
only. Formed of a special microbe of an extreme minuteness, this virus
may be multiplied by artificial culture outside the animal body. These
cultures, left alone without any possible external contamination,
undergo, in the course of time, modifications of their virulency to a
greater or less extent. The oxygen of the atmosphere is said to be
the chief cause of these attenuations--that is, this lessening of the
facilities of multiplication of the microbe; for it is evident that the
difference of virulence is in some way associated with differences of
development in the parasitic economy.

"There is no need to insist upon the interesting character of these
results and the deductions to be made therefrom. To seek to lessen the
virulence by rational means would be to establish, upon an experimental
basis, the hope of preparing from an active virus, easily cultivated
either in the human or animal body, a vaccine-virus of restrained
development capable of preventing the fatal effects of the former.
Therefore, we have applied all our energies to investigate the possible
generalizing action of atmospheric oxygen in the attenuation of virus.

"The anthrax virus, being one that has been most carefully studied,
seemed to be the first that should attract our attention. Every time,
however, we encountered a difficulty. Between the microbe of chicken
cholera and the microbe of anthrax there exists an essential difference
which does not allow the new experiment to be verified by the old.
The microbes of chicken cholera do not, in effect, seem to resolve
themselves, in their culture, into veritable germs. The latter are
merely cells, or articulations always ready to multiply by division,
except when the particular conditions in which they become true germs
are known.

"The yeast of beer is a striking example of these cellular productions,
being able to multiply themselves indefinitely without the apparition
of their original spores. There exist many mucedines (Mucedinae?) of
tubular mushrooms, which in certain conditions of culture produce
a chain of more or less spherical cells called Conidae. The latter,
detached from their branches, are able to reproduce themselves in the
form of cells, without the appearance, at least with a change in the
conditions of culture, of the spores of their respective mucedines.
These vegetable organisms can be compared to plants which are cultivated
by slipping, and to produce which it is not necessary to have the fruits
or the seeds of the mother plant.

"The anthrax bacterium, in its artificial cultivation, behaves very
differently. Its mycelian filaments, if one may so describe them, have
been produced scarcely for twenty-four or forty-eight hours when they
are seen to transform themselves, those especially which are in free
contact with the air, into very refringent corpuscles, capable of
gradually isolating themselves into true germs of slight organization.
Moreover, observation shows that these germs, formed so quickly in the
culture, do not undergo, after exposure for a time to atmospheric air,
any change either in their vitality or their virulence. I was able to
present to the Academy a tube containing some spores of anthrax bacteria
produced four years ago, on March 21, 1887. Each year the germination
of these little corpuscles has been tried, and each year the germination
has been accomplished with the same facility and the same rapidity as at
first. Each year also the virulence of the new cultures has been tested,
and they have not shown any visible falling off. Therefore, how can we
experiment with the action of the air upon the anthrax virus with any
expectation of making it less virulent?

"The crucial difficulty lies perhaps entirely in this rapid reproduction
of the bacteria germs which we have just related. In its form of a
filament, and in its multiplication by division, is not this organism at
all points comparable with the microbe of the chicken cholera?

"That a germ, properly so called, that a seed, does not suffer any
modification on account of the air is easily conceived; but it is
conceivable not less easily that if there should be any change it would
occur by preference in the case of a mycelian fragment. It is thus that
a slip which may have been abandoned in the soil in contact with the air
does not take long to lose all vitality, while under similar conditions
a seed is preserved in readiness to reproduce the plant. If these views
have any foundation, we are led to think that in order to prove the
action of the air upon the anthrax bacteria it will be indispensable to
submit to this action the mycelian development of the minute organism
under conditions where there cannot be the least admixture of
corpuscular germs. Hence the problem of submitting the bacteria to the
action of oxygen comes back to the question of presenting entirely
the formation of spores. The question being put in this way, we are
beginning to recognize that it is capable of being solved.

"We can, in fact, prevent the appearance of spores in the artificial
cultures of the anthrax parasite by various artifices. At the lowest
temperature at which this parasite can be cultivated--that is to say,
about +16 degrees Centigrade--the bacterium does not produce germs--at
any rate, for a very long time. The shapes of the minute microbe at this
lowest limit of its development are irregular, in the form of balls and
pears--in a word, they are monstrosities--but they are without spores.
In the last regard also it is the same at the highest temperatures at
which the parasite can be cultivated, temperatures which vary slightly
according to the means employed. In neutral chicken bouillon the
bacteria cannot be cultivated above 45 degrees. Culture, however, is
easy and abundant at 42 to 43 degrees, but equally without any formation
of spores. Consequently a culture of mycelian bacteria can be kept
entirely free from germs while in contact with the open air at a
temperature of from 42 to 43 degrees Centigrade. Now appear the three
remarkable results. After about one month of waiting the culture
dies--that is to say, if put into a fresh bouillon it becomes absolutely

"So much for the life and nutrition of this organism. In respect to its
virulence, it is an extraordinary fact that it disappears entirely after
eight days' culture at 42 to 43 degrees Centigrade, or, at any rate, the
cultures are innocuous for the guinea-pig, the rabbit, and the sheep,
the three kinds of animals most apt to contract anthrax. We are thus
able to obtain, not only the attenuation of the virulence, but also its
complete suppression by a simple method of cultivation. Moreover, we see
also the possibility of preserving and cultivating the terrible microbe
in an inoffensive state. What is it that happens in these eight days at
43 degrees that suffices to take away the virulence of the bacteria? Let
us remember that the microbe of chicken cholera dies in contact with the
air, in a period somewhat protracted, it is true, but after successive
attenuations. Are we justified in thinking that it ought to be the same
in regard to the microbe of anthrax? This hypothesis is confirmed
by experiment. Before the disappearance of its virulence the anthrax
microbe passes through various degrees of attenuation, and, moreover,
as is also the case with the microbe of chicken cholera, each of these
attenuated states of virulence can be obtained by cultivation. Moreover,
since, according to one of our recent Communications, anthrax is
not recurrent, each of our attenuated anthrax microbes is, for the
better-developed microbe, a vaccine--that is to say, a virus producing a
less-malignant malady. What, therefore, is easier than to find in these
a virus that will infect with anthrax sheep, cows, and horses, without
killing them, and ultimately capable of warding off the mortal malady?
We have practised this experiment with great success upon sheep, and
when the season comes for the assembling of the flocks at Beauce we
shall try the experiment on a larger scale.

"Already M. Toussaint has announced that sheep can be saved by
preventive inoculations; but when this able observer shall have
published his results; on the subject of which we have made such
exhaustive studies, as yet unpublished, we shall be able to see the
whole difference which exists between the two methods--the uncertainty
of the one and the certainty of the other. That which we announce has,
moreover, the very great advantage of resting upon the existence of
a poison vaccine cultivable at will, and which can be increased
indefinitely in the space of a few hours without having recourse to
infected blood."(8)

This announcement was immediately challenged in a way that brought it
to the attention of the entire world. The president of an agricultural
society, realizing the enormous importance of the subject, proposed to
Pasteur that his alleged discovery should be submitted to a decisive
public test. He proposed to furnish a drove of fifty sheep half of which
were to be inoculated with the attenuated virus of Pasteur. Subsequently
all the sheep were to be inoculated with virulent virus, all being kept
together in one pen under precisely the same conditions. The "protected"
sheep were to remain healthy; the unprotected ones to die of anthrax;
so read the terms of the proposition. Pasteur accepted the challenge;
he even permitted a change in the programme by which two goats were
substituted for two of the sheep, and ten cattle added, stipulating,
however, that since his experiments had not yet been extended to cattle
these should not be regarded as falling rigidly within the terms of the

It was a test to try the soul of any man, for all the world looked on
askance, prepared to deride the maker of so preposterous a claim as soon
as his claim should be proved baseless. Not even the fame of Pasteur
could make the public at large, lay or scientific, believe in the
possibility of what he proposed to accomplish. There was time for all
the world to be informed of the procedure, for the first "preventive"
inoculation--or vaccination, as Pasteur termed it--was made on May 5th,
the second on May 17th, and another interval of two weeks must elapse
before the final inoculations with the unattenuated virus. Twenty-four
sheep, one goat, and five cattle were submitted to the preliminary
vaccinations. Then, on May 31 st, all sixty of the animals were
inoculated, a protected and unprotected one alternately, with an
extremely virulent culture of anthrax microbes that had been in
Pasteur's laboratory since 1877. This accomplished, the animals were
left together in one enclosure to await the issue.

Two days later, June 2d, at the appointed hour of rendezvous, a vast
crowd, composed of veterinary surgeons, newspaper correspondents, and
farmers from far and near, gathered to witness the closing scenes of
this scientific tourney. What they saw was one of the most dramatic
scenes in the history of peaceful science--a scene which, as Pasteur
declared afterwards, "amazed the assembly." Scattered about the
enclosure, dead, dying, or manifestly sick unto death, lay the
unprotected animals, one and all, while each and every "protected"
animal stalked unconcernedly about with every appearance of perfect
health. Twenty of the sheep and the one goat were already dead; two
other sheep expired under the eyes of the spectators; the remaining
victims lingered but a few hours longer. Thus in a manner theatrical
enough, not to say tragic, was proclaimed the unequivocal victory of
science. Naturally enough, the unbelievers struck their colors and
surrendered without terms; the principle of protective vaccination,
with a virus experimentally prepared in the laboratory, was established
beyond the reach of controversy.

That memorable scientific battle marked the beginning of a new era
in medicine. It was a foregone conclusion that the principle thus
established would be still further generalized; that it would be
applied to human maladies; that in all probability it would grapple
successfully, sooner or later, with many infectious diseases. That
expectation has advanced rapidly towards realization. Pasteur himself
made the application to the human subject in the disease hydrophobia in
1885, since which time that hitherto most fatal of maladies has largely
lost its terrors. Thousands of persons bitten by mad dogs have been
snatched from the fatal consequences of that mishap by this method at
the Pasteur Institute in Paris, and at the similar institutes, built on
the model of this parent one, that have been established all over the
world in regions as widely separated as New York and Nha-Trang.


In the production of the rabies vaccine Pasteur and his associates
developed a method of attenuation of a virus quite different from that
which had been employed in the case of the vaccines of chicken cholera
and of anthrax. The rabies virus was inoculated into the system of
guinea-pigs or rabbits and, in effect, cultivated in the systems of
these animals. The spinal cord of these infected animals was found to
be rich in the virus, which rapidly became attenuated when the cord was
dried in the air. The preventive virus, of varying strengths, was made
by maceration of these cords at varying stages of desiccation. This
cultivation of a virus within the animal organism suggested, no doubt,
by the familiar Jennerian method of securing small-pox vaccine, was at
the same time a step in the direction of a new therapeutic procedure
which was destined presently to become of all-absorbing importance--the
method, namely, of so-called serum-therapy, or the treatment of a
disease with the blood serum of an animal that has been subjected to
protective inoculation against that disease.

The possibility of such a method was suggested by the familiar
observation, made by Pasteur and numerous other workers, that animals
of different species differ widely in their susceptibility to various
maladies, and that the virus of a given disease may become more and more
virulent when passed through the systems of successive individuals
of one species, and, contrariwise, less and less virulent when passed
through the systems of successive individuals of another species. These
facts suggested the theory that the blood of resistant animals might
contain something directly antagonistic to the virus, and the hope that
this something might be transferred with curative effect to the blood
of an infected susceptible animal. Numerous experimenters all over the
world made investigations along the line of this alluring possibility,
the leaders perhaps being Drs. Behring and Kitasato, closely followed by
Dr. Roux and his associates of the Pasteur Institute of Paris. Definite
results were announced by Behring in 1892 regarding two important
diseases--tetanus and diphtheria--but the method did not come into
general notice until 1894, when Dr. Roux read an epoch-making paper on
the subject at the Congress of Hygiene at Buda-Pesth.

In this paper Dr. Roux, after adverting to the labors of Behring,
Ehrlich, Boer, Kossel, and Wasserman, described in detail the methods
that had been developed at the Pasteur Institute for the development of
the curative serum, to which Behring had given the since-familiar name
antitoxine. The method consists, first, of the cultivation, for some
months, of the diphtheria bacillus (called the Klebs-Loeffler bacillus,
in honor of its discoverers) in an artificial bouillon, for the
development of a powerful toxine capable of giving the disease in a
virulent form.

This toxine, after certain details of mechanical treatment, is injected
in small but increasing doses into the system of an animal, care being
taken to graduate the amount so that the animal does not succumb to the
disease. After a certain course of this treatment it is found that a
portion of blood serum of the animal so treated will act in a curative
way if injected into the blood of another animal, or a human patient,
suffering with diphtheria. In other words, according to theory, an
antitoxine has been developed in the system of the animal subjected to
the progressive inoculations of the diphtheria toxine. In Dr. Roux's
experience the animal best suited for the purpose is the horse, though
almost any of the domesticated animals will serve the purpose.

But Dr. Roux's paper did not stop with the description of laboratory
methods. It told also of the practical application of the serum to
the treatment of numerous cases of diphtheria in the hospitals of
Paris--applications that had met with a gratifying measure of success.
He made it clear that a means had been found of coping successfully with
what had been one of the most virulent and intractable of the diseases
of childhood. Hence it was not strange that his paper made a sensation
in all circles, medical and lay alike.

Physicians from all over the world flocked to Paris to learn the details
of the open secret, and within a few months the new serum-therapy had
an acknowledged standing with the medical profession everywhere. What it
had accomplished was regarded as but an earnest of what the new
method might accomplish presently when applied to the other infectious

Efforts at such applications were immediately begun in numberless
directions--had, indeed, been under way in many a laboratory for some
years before. It is too early yet to speak of the results in detail. But
enough has been done to show that this method also is susceptible of the
widest generalization. It is not easy at the present stage to sift that
which is tentative from that which will be permanent; but so great an
authority as Behring does not hesitate to affirm that today we possess,
in addition to the diphtheria antitoxine, equally specific antitoxines
of tetanus, cholera, typhus fever, pneumonia, and tuberculosis--a set
of diseases which in the aggregate account for a startling proportion
of the general death-rate. Then it is known that Dr. Yersin, with the
collaboration of his former colleagues of the Pasteur Institute, has
developed, and has used with success, an antitoxine from the microbe of
the plague which recently ravaged China.

Dr. Calmette, another graduate of the Pasteur Institute, has extended
the range of the serum-therapy to include the prevention and treatment
of poisoning by venoms, and has developed an antitoxine that has already
given immunity from the lethal effects of snake bites to thousands of
persons in India and Australia.

Just how much of present promise is tentative, just what are the limits
of the methods--these are questions for the future to decide. But, in
any event, there seems little question that the serum treatment will
stand as the culminating achievement in therapeutics of our century.
It is the logical outgrowth of those experimental studies with the
microscope begun by our predecessors of the thirties, and it represents
the present culmination of the rigidly experimental method which has
brought medicine from a level of fanciful empiricism to the plane of a
rational experimental science.



A little over a hundred years ago a reform movement was afoot in the
world in the interests of the insane. As was fitting, the movement
showed itself first in America, where these unfortunates were humanely
cared for at a time when their treatment elsewhere was worse than
brutal; but England and France quickly fell into line. The leader on
this side of the water was the famous Philadelphian, Dr. Benjamin Rush,
"the Sydenham of America"; in England, Dr. William Tuke inaugurated the
movement; and in France, Dr. Philippe Pinel, single-handed, led the way.
Moved by a common spirit, though acting quite independently, these
men raised a revolt against the traditional custom which, spurning the
insane as demon-haunted outcasts, had condemned these unfortunates to
dungeons, chains, and the lash. Hitherto few people had thought it other
than the natural course of events that the "maniac" should be thrust
into a dungeon, and perhaps chained to the wall with the aid of an iron
band riveted permanently about his neck or waist. Many an unfortunate,
thus manacled, was held to the narrow limits of his chain for
years together in a cell to which full daylight never penetrated;
sometimes--iron being expensive--the chain was so short that the
wretched victim could not rise to the upright posture or even shift his
position upon his squalid pallet of straw.

In America, indeed, there being no Middle Age precedents to crystallize
into established customs, the treatment accorded the insane had seldom
or never sunk to this level. Partly for this reason, perhaps, the work
of Dr. Rush at the Philadelphia Hospital, in 1784, by means of which the
insane came to be humanely treated, even to the extent of banishing the
lash, has been but little noted, while the work of the European leaders,
though belonging to later decades, has been made famous. And perhaps
this is not as unjust as it seems, for the step which Rush took, from
relatively bad to good, was a far easier one to take than the leap from
atrocities to good treatment which the European reformers were obliged
to compass. In Paris, for example, Pinel was obliged to ask permission
of the authorities even to make the attempt at liberating the insane
from their chains, and, notwithstanding his recognized position as a
leader of science, he gained but grudging assent, and was regarded as
being himself little better than a lunatic for making so manifestly
unwise and hopeless an attempt. Once the attempt had been made, however,
and carried to a successful issue, the amelioration wrought in the
condition of the insane was so patent that the fame of Pinel's work at
the Bicetre and the Salpetriere went abroad apace. It required, indeed,
many years to complete it in Paris, and a lifetime of effort on the
part of Pinel's pupil Esquirol and others to extend the reform to the
provinces; but the epochal turning-point had been reached with Pinel's
labors of the closing years of the eighteenth century.

The significance of this wise and humane reform, in the present
connection, is the fact that these studies of the insane gave emphasis
to the novel idea, which by-and-by became accepted as beyond question,
that "demoniacal possession" is in reality no more than the outward
expression of a diseased condition of the brain. This realization made
it clear, as never before, how intimately the mind and the body are
linked one to the other. And so it chanced that, in striking the
shackles from the insane, Pinel and his confreres struck a blow also,
unwittingly, at time-honored philosophical traditions. The liberation
of the insane from their dungeons was an augury of the liberation of
psychology from the musty recesses of metaphysics. Hitherto psychology,
in so far as it existed at all, was but the subjective study of
individual minds; in future it must become objective as well, taking
into account also the relations which the mind bears to the body, and in
particular to the brain and nervous system.

The necessity for this collocation was advocated quite as earnestly, and
even more directly, by another worker of this period, whose studies were
allied to those of alienists, and who, even more actively than they,
focalized his attention upon the brain and its functions. This earliest
of specialists in brain studies was a German by birth but Parisian
by adoption, Dr. Franz Joseph Gall, originator of the since-notorious
system of phrenology. The merited disrepute into which this system has
fallen through the exposition of peripatetic charlatans should not
make us forget that Dr. Gall himself was apparently a highly educated
physician, a careful student of the brain and mind according to the best
light of his time, and, withal, an earnest and honest believer in the
validity of the system he had originated. The system itself, taken as a
whole, was hopelessly faulty, yet it was not without its latent germ
of truth, as later studies were to show. How firmly its author himself
believed in it is evidenced by the paper which he contributed to the
French Academy of Sciences in 1808. The paper itself was referred to a
committee of which Pinel and Cuvier were members. The verdict of this
committee was adverse, and justly so; yet the system condemned had at
least one merit which its detractors failed to realize. It popularized
the conception that the brain is the organ of mind. Moreover, by its
insistence it rallied about it a band of scientific supporters, chief of
whom was Dr. Kaspar Spurzlieim, a man of no mean abilities, who became
the propagandist of phrenology in England and in America. Of course such
advocacy and popularity stimulated opposition as well, and out of the
disputations thus arising there grew presently a general interest in the
brain as the organ of mind, quite aside from any preconceptions whatever
as to the doctrines of Gall and Spurzheim.

Prominent among the unprejudiced class of workers who now appeared was
the brilliant young Frenchman Louis Antoine Desmoulins, who studied
first under the tutorage of the famous Magendie, and published jointly
with him a classical work on the nervous system of vertebrates in
1825. Desmoulins made at least one discovery of epochal importance. He
observed that the brains of persons dying in old age were lighter than
the average and gave visible evidence of atrophy, and he reasoned that
such decay is a normal accompaniment of senility. No one nowadays would
question the accuracy of this observation, but the scientific world
was not quite ready for it in 1825; for when Desmoulins announced his
discovery to the French Academy, that august and somewhat patriarchal
body was moved to quite unscientific wrath, and forbade the young
iconoclast the privilege of further hearings. From which it is evident
that the partially liberated spirit of the new psychology had by no
means freed itself altogether, at the close of the first quarter of
the nineteenth century, from the metaphysical cobwebs of its long


While studies of the brain were thus being inaugurated, the nervous
system, which is the channel of communication between the brain and the
outside world, was being interrogated with even more tangible results.
The inaugural discovery was made in 1811 by Dr. (afterwards Sir Charles)
Bell,(1) the famous English surgeon and experimental physiologist.
It consisted of the observation that the anterior roots of the spinal
nerves are given over to the function of conveying motor impulses from
the brain outward, whereas the posterior roots convey solely sensory
impulses to the brain from without. Hitherto it had been supposed that
all nerves have a similar function, and the peculiar distribution of the
spinal nerves had been an unsolved puzzle.

Bell's discovery was epochal; but its full significance was not
appreciated for a decade, nor, indeed, was its validity at first
admitted. In Paris, in particular, then the court of final appeal in
all matters scientific, the alleged discovery was looked at askance, or
quite ignored. But in 1823 the subject was taken up by the recognized
leader of French physiology--Francois Magendie--in the course of his
comprehensive experimental studies of the nervous system, and Bell's
conclusions were subjected to the most rigid experimental tests
and found altogether valid. Bell himself, meanwhile, had turned his
attention to the cranial nerves, and had proved that these also are
divisible into two sets--sensory and motor. Sometimes, indeed, the two
sets of filaments are combined into one nerve cord, but if traced to
their origin these are found to arise from different brain centres. Thus
it was clear that a hitherto unrecognized duality of function pertains
to the entire extra-cranial nervous system. Any impulse sent from the
periphery to the brain must be conveyed along a perfectly definite
channel; the response from the brain, sent out to the peripheral
muscles, must traverse an equally definite and altogether different
course. If either channel is interrupted--as by the section of its
particular nerve tract--the corresponding message is denied transmission
as effectually as an electric current is stopped by the section of the
transmitting wire.

Experimenters everywhere soon confirmed the observations of Bell and
Magendie, and, as always happens after a great discovery, a fresh
impulse was given to investigations in allied fields. Nevertheless, a
full decade elapsed before another discovery of comparable importance
was made. Then Marshall Hall, the most famous of English physicians
of his day, made his classical observations on the phenomena
that henceforth were to be known as reflex action. In 1832, while
experimenting one day with a decapitated newt, he observed that the
headless creature's limbs would contract in direct response to certain
stimuli. Such a response could no longer be secured if the spinal
nerves supplying a part were severed. Hence it was clear that responsive
centres exist in the spinal cord capable of receiving a sensory message
and of transmitting a motor impulse in reply--a function hitherto
supposed to be reserved for the brain. Further studies went to show that
such phenomena of reflex action on the part of centres lying outside the
range of consciousness, both in the spinal cord and in the brain itself,
are extremely common; that, in short, they enter constantly into the
activities of every living organism and have a most important share in
the sum total of vital movements. Hence, Hall's discovery must always
stand as one of the great mile-stones of the advance of neurological

Hall gave an admirably clear and interesting account of his experiments
and conclusions in a paper before the Royal Society, "On the Reflex
Functions of the Medulla Oblongata and the Medulla Spinalis," from
which, as published in the Transactions of the society for 1833, we may
quote at some length:

"In the entire animal, sensation and voluntary motion, functions of
the cerebrum, combine with the functions of the medulla oblongata and
medulla spinalis, and may therefore render it difficult or impossible to
determine those which are peculiar to each; if, in an animal deprived
of the brain, the spinal marrow or the nerves supplying the muscles be
stimulated, those muscles, whether voluntary or respiratory, are equally
thrown into contraction, and, it may be added, equally in the complete
and in the mutilated animal; and, in the case of the nerves, equally in
limbs connected with and detached from the spinal marrow.

"The operation of all these various causes may be designated centric, as
taking place AT, or at least in a direction FROM, central parts of the
nervous system. But there is another function the phenomena of which
are of a totally different order and obey totally different laws, being
excited by causes in a situation which is EXCENTRIC in the nervous
system--that is, distant from the nervous centres. This mode of action
has not, I think, been hitherto distinctly understood by physiologists.

"Many of the phenomena of this principle of action, as they occur in
the limbs, have certainly been observed. But, in the first place, this
function is by no means confined to the limbs; for, while it imparts
to each muscle its appropriate tone, and to each system of muscles its
appropriate equilibrium or balance, it performs the still more important
office of presiding over the orifices and terminations of each of the
internal canals in the animal economy, giving them their due form
and action; and, in the second place, in the instances in which the
phenomena of this function have been noticed, they have been confounded,
as I have stated, with those of sensation and volition; or, if they
have been distinguished from these, they have been too indefinitely
denominated instinctive, or automatic. I have been compelled, therefore,
to adopt some new designation for them, and I shall now give the reasons
for my choice of that which is given in the title of this paper--'Reflex

"This property is characterized by being EXCITED in its action and
REFLEX in its course: in every instance in which it is exerted an
impression made upon the extremities of certain nerves is conveyed to
the medulla oblongata or the medulla spinalis, and is reflected along
the nerves to parts adjacent to, or remote from, that which has received
the impression.

"It is by this reflex character that the function to which I have
alluded is to be distinguished from every other. There are, in the
animal economy, four modes of muscular action, of muscular contraction.
The first is that designated VOLUNTARY: volition, originated in the
cerebrum and spontaneous in its acts, extends its influence along the
spinal marrow and the motor nerves in a DIRECT LINE to the voluntary
muscles. The SECOND is that of RESPIRATION: like volition, the motive
influence in respiration passes in a DIRECT LINE from one point of the
nervous system to certain muscles; but as voluntary motion seems to
originate in the cerebrum, so the respiratory motions originate in
the medulla oblongata: like the voluntary motions, the motions of
respirations are spontaneous; they continue, at least, after the eighth
pair of nerves have been divided. The THIRD kind of muscular action
in the animal economy is that termed involuntary: it depends upon the
principle of irritability and requires the IMMEDIATE application of
a stimulus to the nervo-muscular fibre itself. These three kinds of
muscular motion are well known to physiologists; and I believe they are
all which have been hitherto pointed out. There is, however, a FOURTH,
which subsists, in part, after the voluntary and respiratory motions
have ceased, by the removal of the cerebrum and medulla oblongata, and
which is attached to the medulla spinalis, ceasing itself when this
is removed, and leaving the irritability undiminished. In this kind of
muscular motion the motive influence does not originate in any central
part of the nervous system, but from a distance from that centre; it is
neither spontaneous in its action nor direct in its course; it is, on
the contrary, EXCITED by the application of appropriate stimuli, which
are not, however, applied immediately to the muscular or nervo-muscular
fibre, but to certain membraneous parts, whence the impression is
carried through the medulla, REFLECTED and reconducted to the part
impressed, or conducted to a part remote from it in which muscular
contraction is effected.

"The first three modes of muscular action are known only by actual
movements of muscular contractions. But the reflex function exists as
a continuous muscular action, as a power presiding over organs not
actually in a state of motion, preserving in some, as the glottis, an
open, in others, as the sphincters, a closed form, and in the limbs a
due degree of equilibrium or balanced muscular action--a function not, I
think, hitherto recognized by physiologists.

"The three kinds of muscular motion hitherto known may be distinguished
in another way. The muscles of voluntary motion and of respiration may
be excited by stimulating the nerves which supply them, in any part of
their course, whether at their source as a part of the medulla oblongata
or the medulla spinalis or exterior to the spinal canal: the muscles of
involuntary motion are chiefly excited by the actual contact of stimuli.
In the case of the reflex function alone the muscles are excited by a
stimulus acting mediately and indirectly in a curved and reflex course,
along superficial subcutaneous or submucous nerves proceeding from the
medulla. The first three of these causes of muscular motion may act on
detached limbs or muscles. The last requires the connection with the
medulla to be preserved entire.

"All the kinds of muscular motion may be unduly excited, but the reflex
function is peculiar in being excitable in two modes of action, not
previously subsisting in the animal economy, as in the case of sneezing,
coughing, vomiting, etc. The reflex function also admits of being
permanently diminished or augmented and of taking on some other morbid
forms, of which I shall treat hereafter.

"Before I proceed to the details of the experiments upon which this
disposition rests, it may be well to point out several instances in
illustration of the various sources of and the modes of muscular action
which have been enumerated. None can be more familiar than the act of
swallowing. Yet how complicated is the act! The apprehension of the food
by the teeth and tongue, etc., is voluntary, and cannot, therefore, take
place in an animal from which the cerebrum is removed. The transition of
food over the glottis and along the middle and lower part of the pharynx
depends upon the reflex action: it can take place in animals from which
the cerebrum has been removed or the ninth pair of nerves divided; but
it requires the connection with the medulla oblongata to be preserved
entirely; and the actual contact of some substance which may act as a
stimulus: it is attended by the accurate closure of the glottis and by
the contraction of the pharynx. The completion of the act of deglutition
is dependent upon the stimulus immediately impressed upon the muscular
fibre of the oesophagus, and is the result of excited irritability.

"However plain these observations may have made the fact that there is
a function of the nervous muscular system distinct from sensation, from
the voluntary and respiratory motions, and from irritability, it is
right, in every such inquiry as the present, that the statements and
reasonings should be made with the experiment, as it were, actually
before us. It has already been remarked that the voluntary and
respiratory motions are spontaneous, not necessarily requiring the
agency of a stimulus. If, then, an animal can be placed in such
circumstances that such motions will certainly not take place, the power
of moving remaining, it may be concluded that volition and the motive
influence of respiration are annihilated. Now this is effected by
removing the cerebrum and the medulla oblongata. These facts are fully
proved by the experiments of Legallois and M. Flourens, and by several
which I proceed to detail, for the sake of the opportunity afforded by
doing so of stating the arguments most clearly.

"I divided the spinal marrow of a very lively snake between the second
and third vertebrae. The movements of the animal were immediately before
extremely vigorous and unintermitted. From the moment of the division
of the spinal marrow it lay perfectly tranquil and motionless, with the
exception of occasional gaspings and slight movements of the head.
It became quite evident that this state of quiescence would continue
indefinitely were the animal secured from all external impressions.

"Being now stimulated, the body began to move with great activity, and
continued to do so for a considerable time, each change of position or
situation bringing some fresh part of the surface of the animal into
contact with the table or other objects and renewing the application of

"At length the animal became again quiescent; and being carefully
protected from all external impressions it moved no more, but died in
the precise position and form which it had last assumed.

"It requires a little manoeuvre to perform this experiment successfully:
the motions of the animal must be watched and slowly and cautiously
arrested by opposing some soft substance, as a glove or cotton wool;
they are by this means gradually lulled into quiescence. The slightest
touch with a hard substance, the slightest stimulus, will, on the other
hand, renew the movements on the animal in an active form. But that this
phenomenon does not depend upon sensation is further fully proved by the
facts that the position last assumed, and the stimuli, may be such as
would be attended by extreme or continued pain, if the sensibility were
undestroyed: in one case the animal remained partially suspended over
the acute edge of the table; in others the infliction of punctures and
the application of a lighted taper did not prevent the animal, still
possessed of active powers of motion, from passing into a state of
complete and permanent quiescence."

In summing up this long paper Hall concludes with this sentence: "The
reflex function appears in a word to be the COMPLEMENT of the functions
of the nervous system hitherto known."(2)

All these considerations as to nerve currents and nerve tracts becoming
stock knowledge of science, it was natural that interest should
become stimulated as to the exact character of these nerve tracts in
themselves, and all the more natural in that the perfected microscope
was just now claiming all fields for its own. A troop of observers soon
entered upon the study of the nerves, and the leader here, as in so
many other lines of microscopical research, was no other than Theodor
Schwann. Through his efforts, and with the invaluable aid of such other
workers as Remak, Purkinje, Henle, Muller, and the rest, all the mystery
as to the general characteristics of nerve tracts was cleared away. It
came to be known that in its essentials a nerve tract is a tenuous fibre
or thread of protoplasm stretching between two terminal points in the
organism, one of such termini being usually a cell of the brain
or spinal cord, the other a distribution-point at or near the
periphery--for example, in a muscle or in the skin. Such a fibril may
have about it a protective covering, which is known as the sheath of
Schwann; but the fibril itself is the essential nerve tract; and in
many cases, as Remak presently discovered, the sheath is dispensed with,
particularly in case of the nerves of the so-called sympathetic system.

This sympathetic system of ganglia and nerves, by-the-bye, had long been
a puzzle to the physiologists. Its ganglia, the seeming centre of
the system, usually minute in size and never very large, are found
everywhere through the organism, but in particular are gathered into a
long double chain which lies within the body cavity, outside the spinal
column, and represents the sole nervous system of the non-vertebrated
organisms. Fibrils from these ganglia were seen to join the cranial and
spinal nerve fibrils and to accompany them everywhere, but what special
function they subserved was long a mere matter of conjecture and led to
many absurd speculations. Fact was not substituted for conjecture
until about the year 1851, when the great Frenchman Claude Bernard
conclusively proved that at least one chief function of the sympathetic
fibrils is to cause contraction of the walls of the arterioles of the
system, thus regulating the blood-supply of any given part. Ten years
earlier Henle had demonstrated the existence of annular bands of muscle
fibres in the arterioles, hitherto a much-mooted question, and several
tentative explanations of the action of these fibres had been made,
particularly by the brothers Weber, by Stilling, who, as early as 1840,
had ventured to speak of "vaso-motor" nerves, and by Schiff, who was
hard upon the same track at the time of Bernard's discovery. But a clear
light was not thrown on the subject until Bernard's experiments were
made in 1851. The experiments were soon after confirmed and extended
by Brown-Sequard, Waller, Budge, and numerous others, and henceforth
physiologists felt that they understood how the blood-supply of any
given part is regulated by the nervous system.

In reality, however, they had learned only half the story, as Bernard
himself proved only a few years later by opening up a new and quite
unsuspected chapter. While experimenting in 1858 he discovered that
there are certain nerves supplying the heart which, if stimulated,
cause that organ to relax and cease beating. As the heart is essentially
nothing more than an aggregation of muscles, this phenomenon was utterly
puzzling and without precedent in the experience of physiologists. An
impulse travelling along a motor nerve had been supposed to be able to
cause a muscular contraction and to do nothing else; yet here such an
impulse had exactly the opposite effect. The only tenable explanation
seemed to be that this particular impulse must arrest or inhibit the
action of the impulses that ordinarily cause the heart muscles to
contract. But the idea of such inhibition of one impulse by another was
utterly novel and at first difficult to comprehend. Gradually, however,
the idea took its place in the current knowledge of nerve physiology,
and in time it came to be understood that what happens in the case of
the heart nerve-supply is only a particular case under a very general,
indeed universal, form of nervous action. Growing out of Bernard's
initial discovery came the final understanding that the entire nervous
system is a mechanism of centres subordinate and centres superior, the
action of the one of which may be counteracted and annulled in effect
by the action of the other. This applies not merely to such physical
processes as heart-beats and arterial contraction and relaxing, but
to the most intricate functionings which have their counterpart in
psychical processes as well. Thus the observation of the inhibition of
the heart's action by a nervous impulse furnished the point of departure
for studies that led to a better understanding of the modus operandi of
the mind's activities than had ever previously been attained by the most
subtle of psychologists.


The work of the nerve physiologists had thus an important bearing on
questions of the mind. But there was another company of workers of
this period who made an even more direct assault upon the "citadel of
thought." A remarkable school of workers had been developed in Germany,
the leaders being men who, having more or less of innate metaphysical
bias as a national birthright, had also the instincts of the empirical
scientist, and whose educational equipment included a profound knowledge
not alone of physiology and psychology, but of physics and mathematics
as well. These men undertook the novel task of interrogating the
relations of body and mind from the standpoint of physics. They sought
to apply the vernier and the balance, as far as might be, to the
intangible processes of mind.

The movement had its precursory stages in the early part of the century,
notably in the mathematical psychology of Herbart, but its first
definite output to attract general attention came from the master-hand
of Hermann Helmholtz in 1851. It consisted of the accurate measurement
of the speed of transit of a nervous impulse along a nerve tract. To
make such measurement had been regarded as impossible, it being supposed
that the flight of the nervous impulse was practically instantaneous.
But Helmholtz readily demonstrated the contrary, showing that the
nerve cord is a relatively sluggish message-bearer. According to his
experiments, first performed upon the frog, the nervous "current"
travels less than one hundred feet per second. Other experiments
performed soon afterwards by Helmholtz himself, and by various
followers, chief among whom was Du Bois-Reymond, modified somewhat the
exact figures at first obtained, but did not change the general bearings
of the early results. Thus the nervous impulse was shown to be something
far different, as regards speed of transit, at any rate, from the
electric current to which it had been so often likened. An electric
current would flash halfway round the globe while a nervous impulse
could travel the length of the human body--from a man's foot to his

The tendency to bridge the gulf that hitherto had separated the physical
from the psychical world was further evidenced in the following decade
by Helmholtz's remarkable but highly technical study of the sensations
of sound and of color in connection with their physical causes, in the
course of which he revived the doctrine of color vision which that other
great physiologist and physicist, Thomas Young, had advanced half
a century before. The same tendency was further evidenced by the
appearance, in 1852, of Dr. Hermann Lotze's famous Medizinische
Psychologie, oder Physiologie der Seele, with its challenge of the old
myth of a "vital force." But the most definite expression of the new
movement was signalized in 1860, when Gustav Fechner published his
classical work called Psychophysik. That title introduced a new word
into the vocabulary of science. Fechner explained it by saying, "I mean
by psychophysics an exact theory of the relation between spirit and
body, and, in a general way, between the physical and the psychic
worlds." The title became famous and the brunt of many a controversy.
So also did another phrase which Fechner introduced in the course of
his book--the phrase "physiological psychology." In making that happy
collocation of words Fechner virtually christened a new science.


The chief purport of this classical book of the German
psycho-physiologist was the elaboration and explication of experiments
based on a method introduced more than twenty years earlier by his
countryman E. H. Weber, but which hitherto had failed to attract the
attention it deserved. The method consisted of the measurement and
analysis of the definite relation existing between external stimuli
of varying degrees of intensity (various sounds, for example) and the
mental states they induce. Weber's experiments grew out of the familiar
observation that the nicety of our discriminations of various sounds,
weights, or visual images depends upon the magnitude of each particular
cause of a sensation in its relation with other similar causes. Thus,
for example, we cannot see the stars in the daytime, though they shine
as brightly then as at night. Again, we seldom notice the ticking of a
clock in the daytime, though it may become almost painfully audible in
the silence of the night. Yet again, the difference between an ounce
weight and a two-ounce weight is clearly enough appreciable when we
lift the two, but one cannot discriminate in the same way between a
five-pound weight and a weight of one ounce over five pounds.

This last example, and similar ones for the other senses, gave Weber
the clew to his novel experiments. Reflection upon every-day experiences
made it clear to him that whenever we consider two visual sensations, or
two auditory sensations, or two sensations of weight, in comparison
one with another, there is always a limit to the keenness of our
discrimination, and that this degree of keenness varies, as in the case
of the weights just cited, with the magnitude of the exciting cause.

Weber determined to see whether these common experiences could be
brought within the pale of a general law. His method consisted of making
long series of experiments aimed at the determination, in each case, of
what came to be spoken of as the least observable difference between the
stimuli. Thus if one holds an ounce weight in each hand, and has tiny
weights added to one of them, grain by grain, one does not at first
perceive a difference; but presently, on the addition of a certain
grain, he does become aware of the difference. Noting now how many
grains have been added to produce this effect, we have the weight which
represents the least appreciable difference when the standard is one

Now repeat the experiment, but let the weights be each of five pounds.
Clearly in this case we shall be obliged to add not grains, but drachms,
before a difference between the two heavy weights is perceived. But
whatever the exact amount added, that amount represents the stimulus
producing a just-perceivable sensation of difference when the standard
is five pounds. And so on for indefinite series of weights of varying
magnitudes. Now came Weber's curious discovery. Not only did he find
that in repeated experiments with the same pair of weights the measure
of "just-{p}erceivable difference" remained approximately fixed, but
he found, further, that a remarkable fixed relation exists between
the stimuli of different magnitude. If, for example, he had found it
necessary, in the case of the ounce weights, to add one-fiftieth of an
ounce to the one before a difference was detected, he found also, in the
case of the five-pound weights, that one-fiftieth of five pounds must be
added before producing the same result. And so of all other weights; the
amount added to produce the stimulus of "least-appreciable difference"
always bore the same mathematical relation to the magnitude of the
weight used, be that magnitude great or small.

Weber found that the same thing holds good for the stimuli of the
sensations of sight and of hearing, the differential stimulus bearing
always a fixed ratio to the total magnitude of the stimuli. Here, then,
was the law he had sought.

Weber's results were definite enough and striking enough, yet they
failed to attract any considerable measure of attention until they were
revived and extended by Fechner and brought before the world in the
famous work on psycho-physics. Then they precipitated a veritable
melee. Fechner had not alone verified the earlier results (with certain
limitations not essential to the present consideration), but had
invented new methods of making similar tests, and had reduced the whole
question to mathematical treatment. He pronounced Weber's discovery
the fundamental law of psycho-physics. In honor of the discoverer,
he christened it Weber's Law. He clothed the law in words and in
mathematical formulae, and, so to say, launched it full tilt at the
heads of the psychological world. It made a fine commotion, be assured,
for it was the first widely heralded bulletin of the new psychology
in its march upon the strongholds of the time-honored metaphysics. The
accomplishments of the microscopists and the nerve physiologists had
been but preliminary--mere border skirmishes of uncertain import. But
here was proof that the iconoclastic movement meant to invade the very
heart of the sacred territory of mind--a territory from which tangible
objective fact had been supposed to be forever barred.


Hardly had the alarm been sounded, however, before a new movement was
made. While Fechner's book was fresh from the press, steps were being
taken to extend the methods of the physicist in yet another way to
the intimate processes of the mind. As Helmholtz had shown the rate of
nervous impulsion along the nerve tract to be measurable, it was
now sought to measure also the time required for the central nervous
mechanism to perform its work of receiving a message and sending out
a response. This was coming down to the very threshold of mind. The
attempt was first made by Professor Donders in 1861, but definitive
results were only obtained after many years of experiment on the part
of a host of observers. The chief of these, and the man who has stood
in the forefront of the new movement and has been its recognized leader
throughout the remainder of the century, is Dr. Wilhelm Wundt, of

The task was not easy, but, in the long run, it was accomplished. Not
alone was it shown that the nerve centre requires a measurable time for
its operations, but much was learned as to conditions that modify this
time. Thus it was found that different persons vary in the rate of their
central nervous activity--which explained the "personal equation" that
the astronomer Bessel had noted a half-century before. It was found,
too, that the rate of activity varies also for the same person under
different conditions, becoming retarded, for example, under influence of
fatigue, or in case of certain diseases of the brain. All details aside,
the essential fact emerges, as an experimental demonstration, that the
intellectual processes--sensation, apperception, volition--are linked
irrevocably with the activities of the central nervous tissues, and
that these activities, like all other physical processes, have a time
element. To that old school of psychologists, who scarcely cared more
for the human head than for the heels--being interested only in the
mind--such a linking of mind and body as was thus demonstrated was
naturally disquieting. But whatever the inferences, there was no
escaping the facts.

Of course this new movement has not been confined to Germany. Indeed,
it had long had exponents elsewhere. Thus in England, a full century
earlier, Dr. Hartley had championed the theory of the close and
indissoluble dependence of the mind upon the brain, and formulated
a famous vibration theory of association that still merits careful
consideration. Then, too, in France, at the beginning of the century,
there was Dr. Cabanis with his tangible, if crudely phrased, doctrine
that the brain digests impressions and secretes thought as the stomach
digests food and the liver secretes bile. Moreover, Herbert Spencer's
Principles of Psychology, with its avowed co-ordination of mind and body
and its vitalizing theory of evolution, appeared in 1855, half a
decade before the work of Fechner. But these influences, though of vast
educational value, were theoretical rather than demonstrative, and the
fact remains that the experimental work which first attempted to gauge
mental operations by physical principles was mainly done in Germany.
Wundt's Physiological Psychology, with its full preliminary descriptions
of the anatomy of the nervous system, gave tangible expression to the
growth of the new movement in 1874; and four years later, with the
opening of his laboratory of physiological psychology at the University
of Leipzig, the new psychology may be said to have gained a permanent
foothold and to have forced itself into official recognition. From then
on its conquest of the world was but a matter of time.

It should be noted, however, that there is one other method of strictly
experimental examination of the mental field, latterly much in vogue,
which had a different origin. This is the scientific investigation of
the phenomena of hypnotism. This subject was rescued from the hands of
charlatans, rechristened, and subjected to accurate investigation by
Dr. James Braid, of Manchester, as early as 1841. But his results, after
attracting momentary attention, fell from view, and, despite desultory
efforts, the subject was not again accorded a general hearing from
the scientific world until 1878, when Dr. Charcot took it up at
the Salpetriere, in Paris, followed soon afterwards by Dr. Rudolf
Heidenhain, of Breslau, and a host of other experimenters. The value
of the method in the study of mental states was soon apparent. Most
of Braid's experiments were repeated, and in the main his results were
confirmed. His explanation of hypnotism, or artificial somnambulism,
as a self-induced state, independent of any occult or supersensible
influence, soon gained general credence. His belief that the initial
stages are due to fatigue of nervous centres, usually from excessive
stimulation, has not been supplanted, though supplemented by notions
growing out of the new knowledge as to subconscious mentality in
general, and the inhibitory influence of one centre over another in the
central nervous mechanism.


These studies of the psychologists and pathologists bring the relations
of mind and body into sharp relief. But even more definite in this
regard was the work of the brain physiologists. Chief of these, during
the middle period of the century, was the man who is sometimes spoken of
as the "father of brain physiology," Marie Jean Pierre Flourens, of the
Jardin des Plantes of Paris, the pupil and worthy successor of Magendie.
His experiments in nerve physiology were begun in the first quarter of
the century, but his local experiments upon the brain itself were
not culminated until about 1842. At this time the old dispute over
phrenology had broken out afresh, and the studies of Flourens were
aimed, in part at least, at the strictly scientific investigation of
this troublesome topic.

In the course of these studies Flourens discovered that in the medulla
oblongata, the part of the brain which connects that organ with the
spinal cord, there is a centre of minute size which cannot be injured in
the least without causing the instant death of the animal operated upon.
It may be added that it is this spot which is reached by the needle of
the garroter in Spanish executions, and that the same centre also is
destroyed when a criminal is "successfully" hanged, this time by the
forced intrusion of a process of the second cervical vertebra. Flourens
named this spot the "vital knot." Its extreme importance, as is now
understood, is due to the fact that it is the centre of nerves that
supply the heart; but this simple explanation, annulling the conception
of a specific "life centre," was not at once apparent.

Other experiments of Flourens seemed to show that the cerebellum is the
seat of the centres that co-ordinate muscular activities, and that the
higher intellectual faculties are relegated to the cerebrum. But beyond
this, as regards localization, experiment faltered. Negative results, as
regards specific faculties, were obtained from all localized irritations
of the cerebrum, and Flourens was forced to conclude that the cerebral
lobe, while being undoubtedly the seat of higher intellection, performs
its functions with its entire structure. This conclusion, which
incidentally gave a quietus to phrenology, was accepted generally, and
became the stock doctrine of cerebral physiology for a generation.

It will be seen, however, that these studies of Flourens had a double
bearing. They denied localization of cerebral functions, but they
demonstrated the localization of certain nervous processes in other
portions of the brain. On the whole, then, they spoke positively for the
principle of localization of function in the brain, for which a certain
number of students contended; while their evidence against cerebral
localization was only negative. There was here and there an observer who
felt that this negative testimony was not conclusive. In particular,
the German anatomist Meynert, who had studied the disposition of nerve
tracts in the cerebrum, was led to believe that the anterior portions of
the cerebrum must have motor functions in preponderance; the posterior
positions, sensory functions. Somewhat similar conclusions were reached
also by Dr. Hughlings-Jackson, in England, from his studies of epilepsy.
But no positive evidence was forthcoming until 1861, when Dr. Paul Broca
brought before the Academy of Medicine in Paris a case of brain lesion
which he regarded as having most important bearings on the question of
cerebral localization.

The case was that of a patient at the Bicetre, who for twenty years had
been deprived of the power of speech, seemingly through loss of memory
of words. In 1861 this patient died, and an autopsy revealed that a
certain convolution of the left frontal lobe of his cerebrum had been
totally destroyed by disease, the remainder of his brain being intact.
Broca felt that this observation pointed strongly to a localization
of the memory of words in a definite area of the brain. Moreover, it
transpired that the case was not without precedent. As long ago as
1825 Dr. Boillard had been led, through pathological studies, to locate
definitely a centre for the articulation of words in the frontal lobe,
and here and there other observers had made tentatives in the same
direction. Boillard had even followed the matter up with pertinacity,
but the world was not ready to listen to him. Now, however, in the
half-decade that followed Broca's announcements, interest rose to
fever-beat, and through the efforts of Broca, Boillard, and numerous
others it was proved that a veritable centre having a strange
domination over the memory of articulate words has its seat in the third
convolution of the frontal lobe of the cerebrum, usually in the
left hemisphere. That part of the brain has since been known to the
English-speaking world as the convolution of Broca, a name which,
strangely enough, the discoverer's compatriots have been slow to accept.

This discovery very naturally reopened the entire subject of brain
localization. It was but a short step to the inference that there must
be other definite centres worth the seeking, and various observers set
about searching for them. In 1867 a clew was gained by Eckhard, who,
repeating a forgotten experiment by Haller and Zinn of the previous
century, removed portions of the brain cortex of animals, with the
result of producing convulsions. But the really vital departure was
made in 1870 by the German investigators Fritsch and Hitzig, who, by
stimulating definite areas of the cortex of animals with a galvanic
current, produced contraction of definite sets of muscles of the
opposite side of the body. These most important experiments, received at
first with incredulity, were repeated and extended in 1873 by Dr. David
Ferrier, of London, and soon afterwards by a small army of independent
workers everywhere, prominent among whom were Franck and Pitres in
France, Munck and Goltz in Germany, and Horsley and Schafer in England.
The detailed results, naturally enough, were not at first all in
harmony. Some observers, as Goltz, even denied the validity of the
conclusions in toto. But a consensus of opinion, based on multitudes of
experiments, soon placed the broad general facts for which Fritsch and
Hitzig contended beyond controversy. It was found, indeed, that the
cerebral centres of motor activities have not quite the finality at
first ascribed to them by some observers, since it may often happen
that after the destruction of a centre, with attending loss of function,
there may be a gradual restoration of the lost function, proving that
other centres have acquired the capacity to take the place of the one
destroyed. There are limits to this capacity for substitution, however,
and with this qualification the definiteness of the localization of
motor functions in the cerebral cortex has become an accepted part of
brain physiology.

Nor is such localization confined to motor centres. Later experiments,
particularly of Ferrier and of Munck, proved that the centres of vision
are equally restricted in their location, this time in the posterior
lobes of the brain, and that hearing has likewise its local habitation.
Indeed, there is every reason to believe that each form of primary
sensation is based on impressions which mainly come to a definitely
localized goal in the brain. But all this, be it understood, has no
reference to the higher forms of intellection. All experiment has proved
futile to localize these functions, except indeed to the extent of
corroborating the familiar fact of their dependence upon the brain, and,
somewhat problematically, upon the anterior lobes of the cerebrum in
particular. But this is precisely what should be expected, for the
clearer insight into the nature of mental processes makes it plain that
in the main these alleged "faculties" are not in themselves localized.
Thus, for example, the "faculty" of language is associated irrevocably
with centres of vision, of hearing, and of muscular activity, to go
no further, and only becomes possible through the association of these
widely separated centres. The destruction of Broca's centre, as was
early discovered, does not altogether deprive a patient of his knowledge
of language. He may be totally unable to speak (though as to this there
are all degrees of variation), and yet may comprehend what is said
to him, and be able to read, think, and even write correctly. Thus it
appears that Broca's centre is peculiarly bound up with the capacity for
articulate speech, but is far enough from being the seat of the faculty
of language in its entirety.

In a similar way, most of the supposed isolated "faculties" of higher
intellection appear, upon clearer analysis, as complex aggregations of
primary sensations, and hence necessarily dependent upon numerous and
scattered centres. Some "faculties," as memory and volition, may be
said in a sense to be primordial endowments of every nerve cell--even
of every body cell. Indeed, an ultimate analysis relegates all
intellection, in its primordial adumbrations, to every particle of
living matter. But such refinements of analysis, after all, cannot hide
the fact that certain forms of higher intellection involve a pretty
definite collocation and elaboration of special sensations. Such
specialization, indeed, seems a necessary accompaniment of mental
evolution. That every such specialized function has its localized
centres of co-ordination, of some such significance as the demonstrated
centres of articulate speech, can hardly be in doubt--though this, be it
understood, is an induction, not as yet a demonstration. In other
words, there is every reason to believe that numerous "centres," in
this restricted sense, exist in the brain that have as yet eluded the
investigator. Indeed, the current conception regards the entire cerebral
cortex as chiefly composed of centres of ultimate co-ordination of
impressions, which in their cruder form are received by more primitive
nervous tissues--the basal ganglia, the cerebellum and medulla, and the
spinal cord.

This, of course, is equivalent to postulating the cerebral cortex as
the exclusive seat of higher intellection. This proposition, however,
to which a safe induction seems to lead, is far afield from the
substantiation of the old conception of brain localization, which
was based on faulty psychology and equally faulty inductions from few
premises. The details of Gall's system, as propounded by generations of
his mostly unworthy followers, lie quite beyond the pale of scientific
discussion. Yet, as I have said, a germ of truth was there--the idea
of specialization of cerebral functions--and modern investigators have
rescued that central conception from the phrenological rubbish heap in
which its discoverer unfortunately left it buried.


The common ground of all these various lines of investigations of
pathologist, anatomist, physiologist, physicist, and psychologist is,
clearly, the central nervous system--the spinal cord and the brain.
The importance of these structures as the foci of nervous and mental
activities has been recognized more and more with each new accretion
of knowledge, and the efforts to fathom the secrets of their intimate
structure has been unceasing. For the earlier students, only the
crude methods of gross dissections and microscopical inspection were
available. These could reveal something, but of course the inner secrets
were for the keener insight of the microscopist alone. And even for him
the task of investigation was far from facile, for the central nervous
tissues are the most delicate and fragile, and on many accounts the most
difficult of manipulation of any in the body.

Special methods, therefore, were needed for this essay, and brain
histology has progressed by fitful impulses, each forward jet marking
the introduction of some ingenious improvement of mechanical technique,
which placed a new weapon in the hands of the investigators.

The very beginning was made in 1824 by Rolando, who first thought of
cutting chemically hardened pieces of brain tissues into thin sections
for microscopical examination--the basal structure upon which almost all
the later advances have been conducted. Muller presently discovered that
bichromate of potassium in solution makes the best of fluids for the
preliminary preservation and hardening of the tissues. Stilling, in
1842, perfected the method by introducing the custom of cutting a series
of consecutive sections of the same tissue, in order to trace nerve
tracts and establish spacial relations. Then from time to time
mechanical ingenuity added fresh details of improvement. It was found
that pieces of hardened tissue of extreme delicacy can be made
better subject to manipulation by being impregnated with collodion or
celloidine and embedded in paraffine. Latterly it has become usual
to cut sections also from fresh tissues, unchanged by chemicals, by
freezing them suddenly with vaporized ether or, better, carbonic acid.
By these methods, and with the aid of perfected microtomes, the worker
of recent periods avails himself of sections of brain tissues of a
tenuousness which the early investigators could not approach.

But more important even than the cutting of thin sections is the
process of making the different parts of the section visible, one tissue
differentiated from another. The thin section, as the early workers
examined it, was practically colorless, and even the crudest details of
its structure were made out with extreme difficulty. Remak did, indeed,
manage to discover that the brain tissue is cellular, as early as 1833,
and Ehrenberg in the same year saw that it is also fibrillar, but beyond
this no great advance was made until 1858, when a sudden impulse was
received from a new process introduced by Gerlach. The process itself
was most simple, consisting essentially of nothing more than the
treatment of a microscopical section with a solution of carmine. But the
result was wonderful, for when such a section was placed under the lens
it no longer appeared homogeneous. Sprinkled through its substance were
seen irregular bodies that had taken on a beautiful color, while the
matrix in which they were embedded remained unstained. In a word, the
central nerve cell had sprung suddenly into clear view.

A most interesting body it proved, this nerve cell, or ganglion cell,
as it came to be called. It was seen to be exceedingly minute in size,
requiring high powers of the microscope to make it visible. It exists in
almost infinite numbers, not, however, scattered at random through the
brain and spinal cord. On the contrary, it is confined to those portions
of the central nervous masses which to the naked eye appear gray in
color, being altogether wanting in the white substance which makes up
the chief mass of the brain. Even in the gray matter, though sometimes
thickly distributed, the ganglion cells are never in actual contact one
with another; they always lie embedded in intercellular tissues, which
came to be known, following Virchow, as the neuroglia.

Each ganglion cell was seen to be irregular in contour, and to have
jutting out from it two sets of minute fibres, one set relatively short,
indefinitely numerous, and branching in every direction; the other set
limited in number, sometimes even single, and starting out directly from
the cell as if bent on a longer journey. The numerous filaments came to
be known as protoplasmic processes; the other fibre was named, after its
discoverer, the axis cylinder of Deiters. It was a natural inference,
though not clearly demonstrable in the sections, that these filamentous
processes are the connecting links between the different nerve cells and
also the channels of communication between nerve cells and the periphery
of the body. The white substance of brain and cord, apparently, is made
up of such connecting fibres, thus bringing the different ganglion cells
everywhere into communication one with another.

In the attempt to trace the connecting nerve tracts through this
white substance by either macroscopical or microscopical methods, most
important aid is given by a method originated by Waller in 1852. Earlier
than that, in 1839, Nasse had discovered that a severed nerve cord
degenerates in its peripheral portions. Waller discovered that every
nerve fibre, sensory or motor, has a nerve cell to or from which it
leads, which dominates its nutrition, so that it can only retain its
vitality while its connection with that cell is intact. Such cells he
named trophic centres. Certain cells of the anterior part of the spinal
cord, for example, are the trophic centres of the spinal motor nerves.
Other trophic centres, governing nerve tracts in the spinal cord itself,
are in the various regions of the brain. It occurred to Waller that
by destroying such centres, or by severing the connection at various
regions between a nervous tract and its trophic centre, sharply
defined tracts could be made to degenerate, and their location could
subsequently be accurately defined, as the degenerated tissues take on
a changed aspect, both to macroscopical and microscopical observation.
Recognition of this principle thus gave the experimenter a new weapon
of great efficiency in tracing nervous connections. Moreover, the same
principle has wide application in case of the human subject in disease,
such as the lesion of nerve tracts or the destruction of centres by
localized tumors, by embolisms, or by traumatisms.

All these various methods of anatomical examination combine to make the
conclusion almost unavoidable that the central ganglion cells are the
veritable "centres" of nervous activity to which so many other lines of
research have pointed. The conclusion was strengthened by experiments
of the students of motor localization, which showed that the veritable
centres of their discovery lie, demonstrably, in the gray cortex of the
brain, not in the white matter. But the full proof came from pathology.
At the hands of a multitude of observers it was shown that in certain
well-known diseases of the spinal cord, with resulting paralysis, it is
the ganglion cells themselves that are found to be destroyed. Similarly,
in the case of sufferers from chronic insanities, with marked dementia,
the ganglion cells of the cortex of the brain are found to have
undergone degeneration. The brains of paretics in particular show such
degeneration, in striking correspondence with their mental decadence.
The position of the ganglion cell as the ultimate centre of nervous
activities was thus placed beyond dispute.

Meantime, general acceptance being given the histological scheme of
Gerlach, according to which the mass of the white substance of the
brain is a mesh-work of intercellular fibrils, a proximal idea seemed
attainable of the way in which the ganglionic activities are correlated,
and, through association, built up, so to speak, into the higher mental
processes. Such a conception accorded beautifully with the ideas of
the associationists, who had now become dominant in psychology. But
one standing puzzle attended this otherwise satisfactory correlation
of anatomical observations and psychic analyses. It was this: Since,
according to the histologist, the intercellular fibres, along which
impulses are conveyed, connect each brain cell, directly or indirectly,
with every other brain cell in an endless mesh-work, how is it possible
that various sets of cells may at times be shut off from one another?
Such isolation must take place, for all normal ideation depends for
its integrity quite as much upon the shutting-out of the great mass of
associations as upon the inclusion of certain other associations. For
example, a student in solving a mathematical problem must for the moment
become quite oblivious to the special associations that have to do with
geography, natural history, and the like. But does histology give any
clew to the way in which such isolation may be effected?

Attempts were made to find an answer through consideration of the very
peculiar character of the blood-supply in the brain. Here, as nowhere
else, the terminal twigs of the arteries are arranged in closed systems,
not anastomosing freely with neighboring systems. Clearly, then, a
restricted area of the brain may, through the controlling influence of
the vasomotor nerves, be flushed with arterial blood while neighboring
parts remain relatively anaemic. And since vital activities
unquestionably depend in part upon the supply of arterial blood, this
peculiar arrangement of the vascular mechanism may very properly be
supposed to aid in the localized activities of the central nervous
ganglia. But this explanation left much to be desired--in particular
when it is recalled that all higher intellection must in all probability
involve multitudes of widely scattered centres.

No better explanation was forthcoming, however, until the year 1889,
when of a sudden the mystery was cleared away by a fresh discovery.
Not long before this the Italian histologist Dr. Camille Golgi had
discovered a method of impregnating hardened brain tissues with a
solution of nitrate of silver, with the result of staining the nerve
cells and their processes almost infinitely better than was possible by
the methods of Gerlach, or by any of the multiform methods that other
workers had introduced. Now for the first time it became possible to
trace the cellular prolongations definitely to their termini, for the
finer fibrils had not been rendered visible by any previous method
of treatment. Golgi himself proved that the set of fibrils known as
protoplasmic prolongations terminate by free extremities, and have no
direct connection with any cell save the one from which they spring.
He showed also that the axis cylinders give off multitudes of lateral
branches not hitherto suspected. But here he paused, missing the real
import of the discovery of which he was hard on the track. It remained
for the Spanish histologist Dr. S. Ramon y Cajal to follow up the
investigation by means of an improved application of Golgi's method of
staining, and to demonstrate that the axis cylinders, together with
all their collateral branches, though sometimes extending to a great
distance, yet finally terminate, like the other cell prolongations, in
arborescent fibrils having free extremities. In a word, it was shown
that each central nerve cell, with its fibrillar offshoots, is an
isolated entity. Instead of being in physical connection with a
multitude of other nerve cells, it has no direct physical connection
with any other nerve cell whatever.

When Dr. Cajal announced his discovery, in 1889, his revolutionary
claims not unnaturally amazed the mass of histologists. There were some
few of them, however, who were not quite unprepared for the revelation;
in particular His, who had half suspected the independence of the cells,
because they seemed to develop from dissociated centres; and Forel,
who based a similar suspicion on the fact that he had never been able
actually to trace a fibre from one cell to another. These observers
then came readily to repeat Cajal's experiments. So also did the veteran
histologist Kolliker, and soon afterwards all the leaders everywhere.
The result was a practically unanimous confirmation of the Spanish
histologist's claims, and within a few months after his announcements
the old theory of union of nerve cells into an endless mesh-work was
completely discarded, and the theory of isolated nerve elements--the
theory of neurons, as it came to be called--was fully established in its

As to how these isolated nerve cells functionate, Dr. Cajal gave the
clew from the very first, and his explanation has met with universal

In the modified view, the nerve cell retains its old position as the
storehouse of nervous energy. Each of the filaments jutting out from the
cell is held, as before, to be indeed a transmitter of impulses, but a
transmitter that operates intermittently, like a telephone wire that is
not always "connected," and, like that wire, the nerve fibril operates
by contact and not by continuity. Under proper stimulation the ends of
the fibrils reach out, come in contact with other end fibrils of other
cells, and conduct their destined impulse. Again they retract, and
communication ceases for the time between those particular cells.
Meantime, by a different arrangement of the various conductors,
different sets of cells are placed in communication, different
associations of nervous impulses induced, different trains of thought
engendered. Each fibril when retracted becomes a non-conductor, but when
extended and in contact with another fibril, or with the body of another
cell, it conducts its message as readily as a continuous filament could
do--precisely as in the case of an electric wire.

This conception, founded on a most tangible anatomical basis, enables
us to answer the question as to how ideas are isolated, and also, as Dr.
Cajal points out, throws new light on many other mental processes.
One can imagine, for example, by keeping in mind the flexible nerve
prolongations, how new trains of thought may be engendered through novel
associations of cells; how facility of thought or of action in certain
directions is acquired through the habitual making of certain nerve-cell
connections; how certain bits of knowledge may escape our memory and
refuse to be found for a time because of a temporary incapacity of the
nerve cells to make the proper connections, and so on indefinitely.

If one likens each nerve cell to a central telephone office, each of
its filamentous prolongations to a telephone wire, one can imagine a
striking analogy between the modus operandi of nervous processes and
of the telephone system. The utility of new connections at the central
office, the uselessness of the mechanism when the connections cannot
be made, the "wires in use" that retard your message, perhaps even the
crossing of wires, bringing you a jangle of sounds far different from
what you desire--all these and a multiplicity of other things that will
suggest themselves to every user of the telephone may be imagined as
being almost ludicrously paralleled in the operations of the nervous
mechanism. And that parallel, startling as it may seem, is not a mere
futile imagining. It is sustained and rendered plausible by a sound
substratum of knowledge of the anatomical conditions under which the
central nervous mechanism exists, and in default of which, as pathology
demonstrates with no less certitude, its functionings are futile to
produce the normal manifestations of higher intellection.



Conspicuously placed in the great hall of Egyptian antiquities in the
British Museum is a wonderful piece of sculpture known as the Rosetta
Stone. I doubt if any other piece in the entire exhibit attracts so much
attention from the casual visitor as this slab of black basalt on its
telescope-like pedestal. The hall itself, despite its profusion of
strangely sculptured treasures, is never crowded, but before this stone
you may almost always find some one standing, gazing with more or less
of discernment at the strange characters that are graven neatly across
its upturned, glass-protected face. A glance at this graven surface
suffices to show that three sets of inscriptions are recorded there.
The upper one, occupying about one-fourth of the surface, is a pictured
scroll, made up of chains of those strange outlines of serpents, hawks,
lions, and so on, which are recognized, even by the least initiated,
as hieroglyphics. The middle inscription, made up of lines, angles,
and half-pictures, one might surmise to be a sort of abbreviated
or short-hand hieroglyphic. The third or lower inscription is
Greek--obviously a thing of words. If the screeds above be also made of
words, only the elect have any way of proving the fact.

Fortunately, however, even the least scholarly observer is left in
no doubt as to the real import of the thing he sees, for an obliging
English label tells us that these three inscriptions are renderings of
the same message, and that this message is a "decree of the priests
of Memphis conferring divine honors on Ptolemy V. (Epiphenes), King of
Egypt, B.C. 195." The label goes on to state that the upper inscription
(of which, unfortunately, only part of the last dozen lines or so
remains, the slab being broken) is in "the Egyptian language, in
hieroglyphics, or writing of the priests"; the second inscription "in
the same language is in Demotic, or the writing of the people"; and
the third "the Greek language and character." Following this is a brief
biography of the Rosetta Stone itself, as follows: "The stone was found
by the French in 1798 among the ruins of Fort Saint Julien, near the
Rosetta mouth of the Nile. It passed into the hands of the British by
the treaty of Alexandria, and was deposited in the British Museum in
the year 1801." There is a whole volume of history in that brief
inscription--and a bitter sting thrown in, if the reader chance to be
a Frenchman. Yet the facts involved could scarcely be suggested more
modestly. They are recorded much more bluntly in a graven inscription
on the side of the stone, which reads: "Captured in Egypt by the British
Army, 1801." No Frenchman could read those words without a veritable
sinking of the heart.

The value of the Rosetta Stone depended on the fact that it gave
promise, even when casually inspected, of furnishing a key to the
centuries-old mystery of the hieroglyphics. For two thousand years the
secret of these strange markings had been forgotten. Nowhere in the
world--quite as little in Egypt as elsewhere--had any man the slightest
clew to their meaning; there were those who even doubted whether these
droll picturings really had any specific meaning, questioning whether
they were not rather vague symbols of esoteric religious import and
nothing more. And it was the Rosetta Stone that gave the answer to
these doubters and restored to the world a lost language and a forgotten

The trustees of the museum recognized at once that the problem of the
Rosetta Stone was one on which the scientists of the world might well
exhaust their ingenuity, and promptly published to the world a carefully
lithographed copy of the entire inscription, so that foreign scholarship
had equal opportunity with the British to try at the riddle. It was an
Englishman, however, who first gained a clew to the solution. This was
none other than the extraordinary Dr. Thomas Young, the demonstrator of
the vibratory nature of light.

Young's specific discoveries were these: (1) That many of the pictures
of the hieroglyphics stand for the names of the objects actually
delineated; (2) that other pictures are sometimes only symbolic; (3)
that plural numbers are represented by repetition; (4) that numerals are
represented by dashes; (5) that hieroglyphics may read either from
the right or from the left, but always from the direction in which the
animal and human figures face; (6) that proper names are surrounded by
a graven oval ring, making what he called a cartouche; (7) that the
cartouches of the preserved portion of the Rosetta Stone stand for the
name of Ptolemy alone; (8) that the presence of a female figure after
such cartouches in other inscriptions always denotes the female sex; (9)
that within the cartouches the hieroglyphic symbols have a positively
phonetic value, either alphabetic or syllabic; and (10) that several
different characters may have the same phonetic value.

Just what these phonetic values are Young pointed out in the case of
fourteen characters representing nine sounds, six of which are accepted
to-day as correctly representing the letters to which he ascribed them,
and the three others as being correct regarding their essential or
consonant element. It is clear, therefore, that he was on the right
track thus far, and on the very verge of complete discovery. But,
unfortunately, he failed to take the next step, which would have been to
realize that the same phonetic values which were given to the alphabetic
characters within the cartouches were often ascribed to them also when
used in the general text of an inscription; in other words, that the
use of an alphabet was not confined to proper names. This was the great
secret which Young missed and which his French successor, Jean Francois
Champollion, working on the foundation that Young had laid, was enabled
to ferret out.

Young's initial studies of the Rosetta Stone were made in 1814; his
later publication bore date of 1819. Champollion's first announcement of
results came in 1822; his second and more important one in 1824. By this
time, through study of the cartouches of other inscriptions, Champollion
had made out almost the complete alphabet, and the "riddle of the
Sphinx" was practically solved. He proved that the Egyptians had
developed a relatively complete alphabet (mostly neglecting the vowels,
as early Semitic alphabets did also) centuries before the Phoenicians
were heard of in history. What relation this alphabet bore to the
Phoenician we shall have occasion to ask in another connection; for the
moment it suffices to know that those strange pictures of the Egyptian
scroll are really letters.

Even this statement, however, must be in a measure modified. These
pictures are letters and something more. Some of them are purely
alphabetical in character and some are symbolic in another way.
Some characters represent syllables. Others stand sometimes as mere
representatives of sounds, and again, in a more extended sense, as
representations of things, such as all hieroglyphics doubtless were
in the beginning. In a word, this is an alphabet, but not a perfected
alphabet, such as modern nations are accustomed to; hence the enormous
complications and difficulties it presented to the early investigators.

Champollion did not live to clear up all these mysteries. His work was
taken up and extended by his pupil Rossellini, and in particular by Dr.
Richard Lepsius in Germany, followed by M. Bernouf, and by Samuel
Birch of the British Museum, and more recently by such well-known
Egyptologists as MM. Maspero and Mariette and Chabas, in France, Dr.
Brugsch, in Germany, and Dr. E. Wallis Budge, the present head of the
Department of Oriental Antiquities at the British Museum. But the
task of later investigators has been largely one of exhumation and
translation of records rather than of finding methods.


The most casual wanderer in the British Museum can hardly fail to notice
two pairs of massive sculptures, in the one case winged bulls, in the
other winged lions, both human-headed, which guard the entrance to the
Egyptian hall, close to the Rosetta Stone. Each pair of these weird
creatures once guarded an entrance to the palace of a king in the famous
city of Nineveh. As one stands before them his mind is carried back over
some twenty-seven intervening centuries, to the days when the "Cedar of
Lebanon" was "fair in his greatness" and the scourge of Israel.

The very Sculptures before us, for example, were perhaps seen by Jonah
when he made that famous voyage to Nineveh some seven or eight hundred
years B.C. A little later the Babylonian and the Mede revolted against
Assyrian tyranny and descended upon the fair city of Nineveh, and almost
literally levelled it to the ground. But these great sculptures, among
other things, escaped destruction, and at once hidden and preserved by
the accumulating debris of the centuries, they stood there age after
age, their very existence quite forgotten. When Xenophon marched past
their site with the ill-starred expedition of the ten thousand, in the
year 400 B.C., he saw only a mound which seemed to mark the site of some
ancient ruin; but the Greek did not suspect that he looked upon the site
of that city which only two centuries before had been the mistress of
the world.

So ephemeral is fame! And yet the moral scarcely holds in the sequel;
for we of to-day, in this new, undreamed-of Western world, behold these
mementos of Assyrian greatness fresh from their twenty-five hundred
years of entombment, and with them records which restore to us the
history of that long-forgotten people in such detail as it was not known
to any previous generation since the fall of Nineveh. For two thousand
five hundred years no one saw these treasures or knew that they existed.
One hundred generations of men came and went without once pronouncing
the name of kings Shalmaneser or Asumazirpal or Asurbanipal. And to-day,
after these centuries of oblivion, these names are restored to
history, and, thanks to the character of their monuments, are assured a
permanency of fame that can almost defy time itself. It would be nothing
strange, but rather in keeping with their previous mutations of fortune,
if the names of Asurnazirpal and Asurbanipal should be familiar as
household words to future generations that have forgotten the existence
of an Alexander, a Caesar, and a Napoleon. For when Macaulay's
prospective New Zealander explores the ruins of the British Museum
the records of the ancient Assyrians will presumably still be there
unscathed, to tell their story as they have told it to our generation,
though every manuscript and printed book may have gone the way of
fragile textures.

But the past of the Assyrian sculptures is quite necromantic enough
without conjuring for them a necromantic future. The story of their
restoration is like a brilliant romance of history. Prior to the middle
of this century the inquiring student could learn in an hour or so all
that was known in fact and in fable of the renowned city of Nineveh. He
had but to read a few chapters of the Bible and a few pages of Diodorus
to exhaust the important literature on the subject. If he turned also to
the pages of Herodotus and Xenophon, of Justin and Aelian, these served
chiefly to confirm the suspicion that the Greeks themselves knew almost
nothing more of the history of their famed Oriental forerunners. The
current fables told of a first King Ninus and his wonderful queen
Semiramis; of Sennacherib the conqueror; of the effeminate Sardanapalus,
who neglected the warlike ways of his ancestors but perished gloriously
at the last, with Nineveh itself, in a self-imposed holocaust. And that
was all. How much of this was history, how much myth, no man could say;
and for all any one suspected to the contrary, no man could ever know.
And to-day the contemporary records of the city are before us in such
profusion as no other nation of antiquity, save Egypt alone, can at all
rival. Whole libraries of Assyrian books are at hand that were written
in the seventh century before our era. These, be it understood, are the
original books themselves, not copies. The author of that remote time
appeals to us directly, hand to eye, without intermediary transcriber.
And there is not a line of any Hebrew or Greek manuscript of a like age
that has been preserved to us; there is little enough that can match
these ancient books by a thousand years. When one reads Moses or
Isaiah, Homer, Hesiod, or Herodotus, he is but following the
transcription--often unquestionably faulty and probably never in all
parts perfect--of successive copyists of later generations. The oldest
known copy of the Bible, for example, dates probably from the fourth
century A.D., a thousand years or more after the last Assyrian records
were made and read and buried and forgotten.

There was at least one king of Assyria--namely, Asurbanipal, whose
palace boasted a library of some ten thousand volumes--a library, if you
please, in which the books were numbered and shelved systematically, and
classified and cared for by an official librarian. If you would see some
of the documents of this marvellous library you have but to step past
the winged lions of Asurnazirpal and enter the Assyrian hall just around
the corner from the Rosetta Stone. Indeed, the great slabs of stone from
which the lions themselves are carved are in a sense books, inasmuch as
there are written records inscribed on their surface. A glance reveals
the strange characters in which these records are written, graven neatly
in straight lines across the stone, and looking to casual inspection
like nothing so much as random flights of arrow-heads. The resemblance
is so striking that this is sometimes called the arrow-head character,
though it is more generally known as the wedge or cuneiform character.
The inscriptions on the flanks of the lions are, however, only makeshift
books. But the veritable books are no farther away than the next room
beyond the hall of Asurnazirpal. They occupy part of a series of cases
placed down the centre of this room. Perhaps it is not too much to speak
of this collection as the most extraordinary set of documents of all the
rare treasures of the British Museum, for it includes not books alone,
but public and private letters, business announcements, marriage
contracts--in a word, all the species of written records that enter into
the every-day life of an intelligent and cultured community.

But by what miracle have such documents been preserved through all these
centuries? A glance makes the secret evident. It is simply a case of
time-defying materials. Each one of these Assyrian documents appears to
be, and in reality is, nothing more or less than an inscribed fragment
of brick, having much the color and texture of a weathered terra-cotta
tile of modern manufacture. These slabs are usually oval or oblong in
shape, and from two or three to six or eight inches in length and
an inch or so in thickness. Each of them was originally a portion of
brick-clay, on which the scribe indented the flights of arrowheads
with some sharp-cornered instrument, after which the document was made
permanent by baking. They are somewhat fragile, of course, as all bricks
are, and many of them have been more or less crumbled in the destruction
of the palace at Nineveh; but to the ravages of mere time they are as
nearly invulnerable as almost anything in nature. Hence it is that these
records of a remote civilization have been preserved to us, while the
similar records of such later civilizations as the Grecian have utterly
perished, much as the flint implements of the cave-dweller come to
us unchanged, while the iron implements of a far more recent age have
crumbled away.


After all, then, granted the choice of materials, there is nothing so
very extraordinary in the mere fact of preservation of these ancient
records. To be sure, it is vastly to the credit of nineteenth-century
enterprise to have searched them out and brought them back to light.
But the real marvel in connection with them is the fact that
nineteenth-century scholarship should have given us, not the material
documents themselves, but a knowledge of their actual contents. The
flight of arrow-heads on wall or slab or tiny brick have surely a
meaning; but how shall we guess that meaning? These must be words; but
what words? The hieroglyphics of the Egyptians were mysterious enough
in all conscience; yet, after all, their symbols have a certain
suggestiveness, whereas there is nothing that seems to promise a mental
leverage in the unbroken succession of these cuneiform dashes. Yet the
Assyrian scholar of to-day can interpret these strange records almost
as readily and as surely as the classical scholar interprets a
Greek manuscript. And this evidences one of the greatest triumphs of
nineteenth-century scholarship, for within almost two thousand years no
man has lived, prior to our century, to whom these strange inscriptions
would not have been as meaningless as they are to the most casual
stroller who looks on them with vague wonderment here in the museum
to-day. For the Assyrian language, like the Egyptian, was veritably a
dead language; not, like Greek and Latin, merely passed from practical
every-day use to the closet of the scholar, but utterly and absolutely
forgotten by all the world. Such being the case, it is nothing less than
marvellous that it should have been restored.

It is but fair to add that this restoration probably never would have
been effected, with Assyrian or with Egyptian, had the language in dying
left no cognate successor; for the powers of modern linguistry, though
great, are not actually miraculous. But, fortunately, a language once
developed is not blotted out in toto; it merely outlives its usefulness
and is gradually supplanted, its successor retaining many traces of its
origin. So, just as Latin, for example, has its living representatives
in Italian and the other Romance tongues, the language of Assyria is
represented by cognate Semitic languages. As it chances, however, these
have been of aid rather in the later stages of Assyrian study than at
the very outset; and the first clew to the message of the cuneiform
writing came through a slightly different channel.

Curiously enough, it was a trilingual inscription that gave the clew, as
in the case of the Rosetta Stone, though with very striking difference
withal. The trilingual inscription now in question, instead of being
a small, portable monument, covers the surface of a massive bluff at
Behistun in western Persia. Moreover, all three of its inscriptions
are in cuneiform characters, and all three are in languages that at
the beginning of our century were absolutely unknown. This inscription
itself, as a striking monument of unknown import, had been seen by
successive generations. Tradition ascribed it, as we learn from Ctesias,
through Diodorus, to the fabled Assyrian queen Semiramis. Tradition
was quite at fault in this; but it is only recently that knowledge has
availed to set it right. The inscription, as is now known, was really
written about the year 515 B.C., at the instance of Darius I., King of
Persia, some of whose deeds it recounts in the three chief languages of
his widely scattered subjects.

The man who at actual risk of life and limb copied this wonderful
inscription, and through interpreting it became the veritable "father of
Assyriology," was the English general Sir Henry Rawlinson. His feat was
another British triumph over the same rivals who had competed for
the Rosetta Stone; for some French explorers had been sent by their
government, some years earlier, expressly to copy this strange record,
and had reported that it was impossible to reach the inscription. But
British courage did not find it so, and in 1835 Rawlinson scaled the
dangerous height and made a paper cast of about half the inscription.
Diplomatic duties called him away from the task for some years, but
in 1848 he returned to it and completed the copy of all parts of the
inscription that have escaped the ravages of time. And now the material
was in hand for a new science, which General Rawlinson himself soon,
assisted by a host of others, proceeded to elaborate.

The key to the value of this unique inscription lies in the fact that
its third language is ancient Persian. It appears that the ancient
Persians had adopted the cuneiform character from their western
neighbors, the Assyrians, but in so doing had made one of those
essential modifications and improvements which are scarcely possible to
accomplish except in the transition from one race to another. Instead
of building with the arrow-head a multitude of syllabic characters,
including many homophones, as had been and continued to be the custom
with the Assyrians, the Persians selected a few of these characters and
ascribed to them phonetic values that were almost purely alphabetic. In
a word, while retaining the wedge as the basal stroke of their script,
they developed an alphabet, making the last wonderful analysis of
phonetic sounds which even to this day has escaped the Chinese, which
the Egyptians had only partially effected, and which the Phoenicians
were accredited by the Greeks with having introduced to the Western
world. In addition to this all-essential step, the Persians had
introduced the minor but highly convenient custom of separating the
words of a sentence from one another by a particular mark, differing
in this regard not only from the Assyrians and Egyptians, but from the
early Greek scribes as well.

Thanks to these simplifications, the old Persian language had been
practically restored about the beginning of the nineteenth century,
through the efforts of the German Grotefend, and further advances in
it were made just at this time by Renouf, in France, and by Lassen, in
Germany, as well as by Rawlinson himself, who largely solved the problem
of the Persian alphabet independently. So the Persian portion of the
Behistun inscription could be at least partially deciphered. This
in itself, however, would have been no very great aid towards the
restoration of the languages of the other portions had it not chanced,
fortunately, that the inscription is sprinkled with proper names. Now
proper names, generally speaking, are not translated from one language
to another, but transliterated as nearly as the genius of the language
will permit. It was the fact that the Greek word Ptolemaics was
transliterated on the Rosetta Stone that gave the first clew to the
sounds of the Egyptian characters. Had the upper part of the Rosetta
Stone been preserved, on which, originally, there were several other
names, Young would not have halted where he did in his decipherment.

But fortune, which had been at once so kind and so tantalizing in the
case of the Rosetta Stone, had dealt more gently with the Behistun
inscriptions; for no fewer than ninety proper names were preserved
in the Persian portion and duplicated, in another character, in the
Assyrian inscription. A study of these gave a clew to the sounds of the
Assyrian characters. The decipherment of this character, however, even
with this aid, proved enormously difficult, for it was soon evident that
here it was no longer a question of a nearly perfect alphabet of a few
characters, but of a syllabary of several hundred characters, including
many homophones, or different forms for representing the same sound.
But with the Persian translation for a guide on the one hand, and the
Semitic languages, to which family the Assyrian belonged, on the other,
the appalling task was gradually accomplished, the leading investigators
being General Rawlinson, Professor Hincks, and Mr. Fox-Talbot, in
England, Professor Jules Oppert, in Paris, and Professor Julian
Schrader, in Germany, though a host of other scholars soon entered the

This great linguistic feat was accomplished about the middle of the
nineteenth century. But so great a feat was it that many scholars of the
highest standing, including Joseph Erneste Renan, in France, and Sir G.
Cornewall Lewis, in England, declined at first to accept the results,
contending that the Assyriologists had merely deceived themselves by
creating an arbitrary language. The matter was put to a test in 1855
at the suggestion of Mr. Fox-Talbot, when four scholars, one being Mr.
Talbot himself and the others General Rawlinson, Professor Hincks,
and Professor Oppert, laid before the Royal Asiatic Society their
independent interpretations of a hitherto untranslated Assyrian text. A
committee of the society, including England's greatest historian of the
century, George Grote, broke the seals of the four translations, and
reported that they found them unequivocally in accord as regards their
main purport, and even surprisingly uniform as regards the phraseology
of certain passages--in short, as closely similar as translations from
the obscure texts of any difficult language ever are. This decision gave
the work of the Assyriologists official status, and the reliability of
their method has never since been in question. Henceforth Assyriology
was an established science.




  (1) Robert Boyle, Philosophical Works (3 vols.). London, 1738.


  (1) For a complete account of the controversy called the "Water
  Controversy," see The Life of the Hon. Henry Cavendish, by George
  Wilson, M.D., F.R.S.E. London, 1850.

  (2) Henry Cavendish, in Phil. Trans. for 1784, P. 119.

  (3) Lives of the Philosophers of the Time of George III., by Henry, Lord
  Brougham, F.R.S., p. 106. London, 1855.

  (4) Experiments and Observations on Different Kinds of Air, by Joseph
  Priestley (3 vols.). Birmingham, 790, vol. II, pp. 103-107.

  (5) Lectures on Experimental Philosophy, by Joseph Priestley, lecture
  IV., pp. 18, ig. J. Johnson, London, 1794.

  (6) Translated from Scheele's Om Brunsten, eller Magnesia, och dess
  Egenakaper. Stockholm, 1774, and published as Alembic Club Reprints, No.
  13, 1897, p. 6.

  (7) According to some writers this was discovered by Berzelius.

  (8) Histoire de la Chimie, par Ferdinand Hoefer. Paris, 1869, Vol. CL,
  p. 289.

  (9) Elements of Chemistry, by Anton Laurent Lavoisier, translated by
  Robert Kerr, p. 8. London and Edinburgh, 1790.

  (10) Ibid., pp. 414-416.


  (1) Sir Humphry Davy, in Phil. Trans., Vol. VIII.


  (1) Baas, History of Medicine, p. 692.

  (2) Based on Thomas H. Huxley's Presidential Address to the British
  Association for the Advancement of Science, 1870.

  (3) Essays on Digestion, by James Carson. London, 1834, p. 6.

  (4) Ibid., p. 7.

  (5) John Hunter, On the Digestion of the Stomach after Death, first
  edition, pp. 183-188.

  (6) Erasmus Darwin, The Botanic Garden, pp. 448-453. London, 1799.


  (1) Baron de Cuvier's Theory of the Earth. New York, 1818, p. 123.

  (2) On the Organs and Mode of Fecundation of Orchidex and Asclepiadea,
  by Robert Brown, Esq., in Miscellaneous Botanical Works. London, 1866,
  Vol. I., pp. 511-514.

  (3) Justin Liebig, Animal Chemistry. London, 1843, p. 17f.


  (1) "Essay on the Metamorphoses of Plants," by Goethe, translated
  for the present work from Grundriss einer Geschichte der
  Naturwissenschaften, by Friederich Dannemann (2 vols.). Leipzig, 1896,
  Vol. I., p. 194.

  (2) The Temple of Nature, or The Origin of Society, by Erasmus Darwin,
  edition published in 1807, p. 35.

  (3) Baron de Cuvier, Theory of the Earth. New York, 1818, p.74. (This
  was the introduction to Cuvier's great work.)

  (4) Robert Chambers, Explanations: a sequel to Vestiges of Creation.
  London, Churchill, 1845, pp. 148-153.


  (1) Condensed from Dr. Boerhaave's Academical Lectures on the Theory of
  Physic. London, 1751, pp. 77, 78. Boerhaave's lectures were published as
  Aphorismi de cognoscendis et curandis Morbis, Leyden, 1709. On this
  book Van Swieten wrote commentaries filling five volumes. Another very
  celebrated work of Boerhaave is his Institutiones et Experimenta
  Chemic, Paris, 1724, the germs of this being given as a lecture on his
  appointment to the chair of chemistry in the University of Leyden in

  (2) An Inquiry into the Causes and Effects of the Variola Vaccine, etc.,
  by Edward Jenner, M.D., F.R.S., etc. London, 1799, pp. 2-7. He wrote
  several other papers, most of which were communications to the Royal
  Society. His last publication was, On the Influence of Artificial
  Eruptions in Certain Diseases (London, 1822), a subject to which he had
  given much time and study.


  (1) In the introduction to Corvisart's translation of Avenbrugger's
  work. Paris, 1808.

  (2) Laennec, Traite d'Auscultation Mediate. Paris, 1819. This was
  Laennec's chief work, and was soon translated into several different
  languages. Before publishing this he had written also, Propositions sur
  la doctrine midicale d'Hippocrate, Paris, 1804, and Memoires sur les
  vers visiculaires, in the same year.

  (3) Researches, Chemical and Philosophical, chiefly concerning Nitrous
  Oxide or Dephlogisticated Nitrous Air and its Respiration, by Humphry
  Davy. London, 1800, pp. 479-556.

  (4) Ibid.

  (5) For accounts of the discovery of anaesthesia, see Report of the
  Board of Trustees of the Massachusetts General Hospital, Boston, 1888.
  Also, The Ether Controversy: Vindication of the Hospital Reports of
  1848, by N. L Bowditch, Boston, 1848. An excellent account is given in
  Littell's Living Age, for March, 1848, written by R. H. Dana, Jr. There
  are also two Congressional Reports on the question of the discovery of
  etherization, one for 1848, the other for 11852.

  (6) Simpson made public this discovery of the anaesthetic properties
  of chloroform in a paper read before the Medico-Chirurgical Society of
  Edinburgh, in March, 1847, about three months after he had first seen
  a surgical operation performed upon a patient to whom ether had been

  (7) Louis Pasteur, Studies on Fermentation. London, 1870.

  (8) Louis Pasteur, in Comptes Rendus des Sciences de L'Academie des
  Sciences, vol. XCII., 1881, pp. 429-435.


  (1) Bell's communications were made to the Royal Society, but his
  studies and his discoveries in the field of anatomy of the nervous
  system were collected and published, in 1824, as An Exposition of the
  Natural System of Nerves of the Human Body: being a Republication of the
  Papers delivered to the Royal Society on the Subject of the Nerves.

  (2) Marshall Hall, M.D., F.R.S.L., On the Reflex Functions of the
  Medulla Oblongata and the Medulla Spinalis, in Phil. Trans. of Royal
  Soc., vol. XXXIII., 1833.

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