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Title: The Sense of Taste
Author: Poffenberger, A. T., Hollingworth, Harry L. (Harry Levi)
Language: English
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                           THE SENSE OF TASTE



------------------------------------------------------------------------



             _Our Senses Series—Editor, G. Van N. Dearborn_

                           THE SENSE OF TASTE

                                   BY

                       H. L. HOLLINGWORTH, PH.D.
        Associate Professor of Psychology in Columbia University

                                  AND

                     A. T. POFFENBERGER, JR., PH.D.
            Instructor in Psychology in Columbia University

                    [Illustration: Publisher’s Logo]

                                NEW YORK
                        MOFFAT, YARD AND COMPANY
                                  1917


------------------------------------------------------------------------



                          Copyright, 1917, by
                        MOFFAT, YARD AND COMPANY



                             --------------

                         Published April, 1917



------------------------------------------------------------------------



                                  _To_
                                L. S. H.
                                  AND
                                F. K. P.



------------------------------------------------------------------------



                         EDITORIAL INTRODUCTION


Few people, comparatively, however intelligent and generally
thoughtful, have as yet stopped to consider the surpassing interest
and the unique importance of Our Senses. Living gateways as the sense
organs are between ourselves and our ever-changing surroundings, both
spiritual and material, they constitute the channels not only of our
_life-satisfaction_, but of all our immediate _knowledge_ as well. If,
then, in discussing them, biological imagination and breadth and depth
go hand in hand with technical knowledge of the highest grade, the
volumes comprised should be both human and scientific. And these
volumes are so, and will be. It is because of such possibilities that
a series like the present, authentic yet interesting and inexpensive,
must appeal to the intelligent man or woman of to-day. As
contributions to psychology and to education their value is certain to
be great, as indeed is indicated by the list of their authors, whom it
would be superfluous to praise or even to portray.

Small in number are the topics in all the wondrous range of the science
of living things that are more alluring for their very mystery and
romance than these same gateways by which we may go out into “our world”
and by which this same great world may come into us and, for the little
span of life, lend us a feeling of home-dwelling.

Within the past decade there has been a general popular awakening from
the former uninterested attitude toward these phenomena of the physical
and mental processes by which we keep in touch with the things outside
ourselves. A fair knowledge of the rudiments of biology, of physiology,
and of psychology now has become part of the curriculum of our schools
and colleges. And of these three sciences it is psychology which has
entered so deeply into our everyday life—business life as well as
personal—that at last no one can escape its influence. And no one wishes
to, for psychology in a sense has become the intellectual handmaiden of
all who think in terms of to-day, with to-day’s amazing development of
insight into the mortal meanings of our very selves, body always as well
as soul. Our scientific realization of our true continuity with all
things else goes on apace, and our personal relations to the boundless,
perhaps Infinite, Cosmos of consciousness, life, and energy seem ever
clearer. Thus, in a way, the sense organs give us personal anchorage in
a Sea which else sometimes, from its very immensity and stress, would
overwhelm us. Our range, although the broadest as yet vouchsafed to
life, is as it were but a mere line out into the complexity of the
Actual. The first step to the appreciation of this complexity and its
implications for the human mind is knowledge of the conditions of its
acquirement,—of the sense organs and of the perplexing brain behind
them.

Editorial duty or privilege fails to know much as yet of the detailed
contents of these several volumes. But the editor does know not a little
about the arrangers and expounders of the volumes’ contents, and he
knows that they are women and men of conspicuous sense—trustworthy in
every sense. The books are the best of their kind and are in a class by
themselves. They are the standard authority for ordinary use. These
volumes when disposed as a red-backed set on one’s library shelf will be
a set of books to be proud of. And the high school boys and girls and
their fathers evenings and on Sundays and their mothers at the club all
alike will think of them as highly valued friends, both wise and
agreeable, as pleasant to meet for an hour as the most welcome visitor
well could be. No higher “authority” exists than that which these
authors represent; and it would be hard to find those who could set
forth “authority” more gracefully. Each knows that literary _enjoyment_
usually goes hand in hand with that _wisdom_ which extended is the
director of Life itself.

Although the sense of taste is more strictly a “biological” sense than
any of the other simple senses of man—that is, more particularly
concerned with the underlying bodily life—it plays, nevertheless, a very
important part in our personal psychology. Many of us find in tasting
one of the fairly dependable satisfactions of our everyday living; and
Satisfaction, it seems upon long reflection, comes pretty close to being
the long-sought “highest good.” The wholly needless and harmful bodily
overweight of many of us attests how often this sense is made a
malignant fetish to lure us evilward. Eve tasted—and in that alluring
moment set an example too plain and too significant ever to be ignored.
The sense of taste, none the less, is a wholly respectable and dignified
mode of obtaining satisfaction.

And our respective “research magnificent” would _not_ be quite so
interesting, not so adventuresome, were our sense of taste, instead of a
clear sense experience tingling always with some kind of satisfaction,
were it, I say, only a subconscious instinct, part of the original
organic nature of man, working in the dark of consciousness. And for a
few of us, especially if we be chefs, or cooks, or tea-tasters, or
dyspeptics, or epicures, or gluttons, or taste-perverts, and the like,
taste is, perhaps, one of the most important of all mortal experiences
and of all scientific themes. And to the children how _much_ it is!

Professor Hollingworth and his Columbia colleague, Doctor Poffenberger,
have written a volume which seemingly would satisfy both the scientific
reader and the general readers who from curiosity seek its information.
The business man as well as his wife sitting beyond the living-room
table will both find the something they hoped to find; and the keen
school teacher and the all too infrequent schoolmaster will find part of
that material for the development of intensive sense-training now
obviously indispensable to the further evolution of our school system.
For even taste, least intellectual of our senses, can be intensively and
hence usefully trained and thus education be furthered.

The authors need no introduction to the educated million, but if they
did, this book would furnish one which the most exclusive hardly could
disdain. They are to be congratulated on the success with which they
have put much that is at once interesting and scientific up to the hour
into little space, with “war-time economy.” The authors have covered
their field well.

                  *       *       *       *       *

The editor takes this first opportunity to invite criticism of whatever
trend, and to ask for suggestions, whether from sense-gluttons or from
philosophers, for the better conduct and the furtherance of this series
and of that other series, on “The Life of the Child,” which he is
editing. As is true in a wholly different field of conquest, here, too,
lies safety in numbers, and where there are many men there are many
minds. As all authors at least will hasten to agree, not even an editor
knows all that might be known.

                                                                G.V.N.D.

    CAMBRIDGE, MASSACHUSETTS,
          _January, 1917_.


------------------------------------------------------------------------



                                PREFACE


The sense of taste is in numerous ways the most paradoxical of all the
senses. Although, as a source of sense impression, it can afford the
keenest immediate feelings of pleasure and delight, the books on
æsthetics and art have little or nothing to say about it. Skill in the
compounding of tastes and flavors, or discrimination in their relish,
brings the expert neither artistic recognition nor social eminence.
Taste, it is constantly asserted, is one of the “lower senses,” and
neither in the enjoyment of it nor the ministration to it is there to be
acquired the merit and general esteem that readily distinguish an art
from a service.

Nevertheless we commonly use the word “taste” for the expression of just
those qualities of fine discrimination and delicate perception which are
most conspicuously the marks of æsthetic appreciation. In our choice of
figures of speech we reserve “vision” for the impersonal and remote
intuition of the seer and the philosopher. “Touch” we use to express
such intimate and personal impressions as sympathy and pity. “Sound”
seems best to indicate, through “noise” or “tone,” either the
self-seeking clamor of aggression or the mere passive possession of a
certain richness of quality. “Odor,” in its most common figurative use,
suggests the reprehensible and undesirable motive. “Warmth” and “chill”
bespeak at once the depth of emotion or affection. But the special
fineness of soul which shows itself in the active and judicious choice
of the appropriate and the harmonious, the subtly fitting and the
delicately adapted, seems best expressed by the name of one of the
“lowest” and most “vulgar” of senses,—“taste.” Whether the judgment be
exercised in the choice of color harmony or musical composition, costume
or personal ornament, architecture, monument, design or arrangement,
poetry or passing jest, rug, menu, pastime or associates, it is the
sense of taste which furnishes the apt name for the critical capacity.

Not only is it in the usages of language that taste is a paradoxical
sense; it is at the same time one of the most ancient of the special
senses and also one about which exact knowledge is most difficult to
acquire. It seems to afford a multitude of varying and distinctive
_nuances_ of sensation, yet it can boast but a meager equipment of four
fundamental sense qualities. It is a primitive and well-established
sense in the evolution of man, and individuals might therefore be
expected to resemble each other closely in their experience of it; yet
the most trite of proverbs insists that “there is no accounting for
tastes.” Indeed, in some languages it is even impossible to find
distinctive names for such common taste experiences as bitter or even
salt and sour. A survey of the phenomena and laws of the sense of taste
reveals, in fact, no end of curious and interesting situations.

Of particular interest are the recent demonstrations of the great
importance of taste for the general well-being of the organism. With the
development of civilized modes of living men cease to rely implicitly or
entirely on the sense of taste in their discrimination between wholesome
and deleterious foods. They substitute for taste the evidence of the
commercial trade-mark, the label, and the pure-food guarantee. It might
have been supposed that under such circumstances the sense of taste
would deteriorate through loss of function. But recent studies show that
sensations of taste do far more than serve as clues to the acceptance or
rejection of food. Such sensations appear, in fact, to be the initial
stimulus to the whole series of digestive and assimilative processes on
which the well-being of the organism depends. In much the same way the
dulling or perversion of the taste sensations is often seen to
constitute an early warning of grave disorder in the system as a whole,
and their restoration to presage the return to normal health.

Developing as one of the earliest forms of sensitiveness, intimately
associated with the vital processes of life and growth, affording
manifold richness of pleasure and aversion, full of paradoxical
surprises and puzzling problems, and figuratively expressing one of the
rarest of human qualities, “the sense of taste” constitutes one of man’s
most interesting contacts with the outer world.

In the chapters which follow an attempt is made to portray this contact
in a manner which is both clear and concrete, yet scientifically
accurate and technically complete. There are first considered the actual
experiences which the sense of taste affords, their character, their
analysis into the elementary qualities, and the classification,
relations, and manner of combination of these qualities. A consideration
of the delicacy of the taste sense, the precision of taste
discrimination, and their methods of measurement, is followed by a
discussion of the time relations of taste sensations, and a description
of various special characteristics and phenomena of normal and abnormal
tastes.

At this point there is presented a detailed description and illustration
of the mechanism and function of the organ of taste, its gross structure
and anatomy, its accessory apparatus, its more minute nervous basis and
composition, and its evolution in the individual and in the lower animal
forms. Chapters are given to the nature of the external stimulus which
provokes taste sensations, to disorders of the taste sense, to the
differences between individuals, and to the function of sensations of
taste in the higher mental processes of imagination, association,
memory, and emotion. Finally, an account of the function of taste in the
life of the organism is followed by a consideration of the place of the
sense of taste in æsthetics and art, and in the complex interplay of
human thought and social communication.


------------------------------------------------------------------------



                                CONTENTS


        CHAPTER                                            PAGE

                EDITORIAL INTRODUCTION                      vii

                PREFACE                                    xiii

              I THE QUALITIES OF TASTE                        1
                  The Taste Manifold—The Classification
                  of Tastes—Taste Blends and Fusions—The
                  Poverty of Taste—Psychological
                  Analysis of the Taste
                  Qualities—Distribution of the Taste
                  Qualities—The Vocabulary of Taste.

             II THE ORGANIZATION OF THE TASTES               27
                  System and Organization in Other
                  Senses—Taste Mixtures and
                  Compounds—Compensation, Antagonism,
                  and Neutralization—Contrast
                  Phenomena—After Images of Taste—The
                  Schema of Taste Relations.

            III THE SENSITIVENESS OF TASTE                   43
                  Various Measures of Sensitiveness—The
                  Threshold of Taste Sensation—Relative
                  Sensitivity of Taste and Smell—The
                  Discrimination of Tastes—Adaptation
                  and Fatigue—Acquired Tastes—The Early
                  Development of Taste.

             IV TIME RELATIONS OF TASTE QUALITIES            55
                  The Inertia of the Taste
                  Organs—Reaction Time to Taste
                  Stimuli—Determinants of Reaction Time
                  to Taste.

              V THE SENSE ORGAN OF TASTE                     60
                  Comparison with other Sense Organs—The
                  Salivary Glands and Their Activity—The
                  Tongue: Its Muscles and Covering
                  Membranes—Classification of
                  Papillæ—The Determination of the Taste
                  Areas.

             VI SENSORY ELEMENTS OF THE TASTE MECHANISM      78
                  Taste Buds and Their General
                  Characteristics—Supporting Cells,
                  Gustatory Cells, and Nerve
                  Filaments—Relations Among the
                  Structures within the Taste Bud—The
                  Sensory Nerves of Taste—The Cerebral
                  Taste Centers.

            VII TASTE-PRODUCING SUBSTANCES                   92
                  Adequate and Inadequate
                  Stimuli—Adequate Taste
                  Stimuli—Inadequate Taste Stimuli.

           VIII THE FUNCTION OF THE TASTE MECHANISM         103
                  The Function of Tongue and Salivary
                  Glands—The Function of the Taste Buds.

             IX THE DEVELOPMENT OF TASTE IN  THE            116
                  INDIVIDUAL
                  Development Before Birth—Development
                  of Taste in Infancy and
                  Childhood—Taste in the
                  Adult—Structural and Functional
                  Differences Among
                  Individuals—Individual Differences Due
                  to Pathological Changes—Racial
                  Differences in the Structure and
                  Function of the Taste Organs.

              X EVOLUTION OF TASTE                          128
                  Sensitivity of the Unicellular
                  Organisms—“The Chemical
                  Sense”—Chemical Sense in
                  Fishes—Land-Dwelling Animals.

             XI GUSTATORY IMAGINATION AND MEMORY            144
                  The Nature and Frequency of Mental
                  Images—Mental Images of Taste—Taste in
                  Dreams and in Hallucinations.

            XII UNUSUAL AND ABNORMAL TASTE EXPERIENCES      151
                  Gustatory Hallucinations and
                  Auræ—Partial and Complete
                  Ageusia—Taste Hallucinations of the
                  Insane—Synæsthesias of
                  Taste—Perversions of Taste.

           XIII FOOD AND FLAVOR                             158
                  The Biological Rôle of Taste—Taste and
                  Digestion—Experimental Evidences—The
                  Function of Taste in the Organic
                  Economy.

            XIV THE ÆSTHETIC VALUE OF TASTE                 168
                  The Higher and Lower Senses—Bounty of
                  Nature and Ecclesiastical
                  Censorship—The Psychophysical
                  Attributes—The Tendency to
                  Adaptation—Spatial Attributes of Taste
                  Qualities—Immediate Affective Value of
                  Taste—Development in the Individual
                  and the Race—The Imaginative Value of
                  Taste—The Non-Social Character of the
                  Lower Senses—The Unsystematic
                  Relations of Taste Qualities—The
                  Motive of Æsthetic Products.

                INDEX                                       197


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                             ILLUSTRATIONS


             Diagram showing relations between the      40
               taste qualities

             Sketch of the tongue                       69

             Diagram showing some of the various        88
               courses which have been advocated for
               the taste fibers in man


------------------------------------------------------------------------



                           THE SENSE OF TASTE



                               CHAPTER I

                         THE QUALITIES OF TASTE

                          _The Taste Manifold_


THE casual observer would probably feel that any attempt to enumerate
and arrange in a logical scheme the infinitude of tastes and flavors
would be an impossible task. To him it might seem that nearly everything
in the world possessed its own peculiar taste. Such an observer would
also be likely to think it impossible and thankless to attempt to reduce
to their necessary limits the various kinds of substance of which this
infinitude of things is made up. But the chemist would readily be able
to show him that the infinitude of substances consisted, as a matter of
fact, only of various forms and combinations of less than one hundred
“elements,” and that from these elements one could produce, by
appropriate selection and apportionment, any one of the infinitude of
substances.

Is it then possible, in the field of our sensations, to reduce to
elemental categories or units the manifold[1] of concrete sense
experience? In the case of visual sensations almost everybody knows that
there are certain so-called “primary” colors, from which can be produced
the whole range of color experiences known to man. Blue and yellow, red
and green, these are the primary colors, and if to these, in their
varying intensities, be added gray, with its range of brightnesses, we
have the elementary components of all our visual experience. Such a
distinctive color as that of fire clay, for example, may thus be said to
contain, in specified degree and proportion, red, yellow, and gray,
while the familiar color of a wild flower may contain, in specified
relations, red, blue, and gray.

Footnote 1:

  By a “manifold” is meant a great variety of objects or experiences
  organized into one system or constituting one field.

In a strict psychological sense, it remains true that each color
experience is relatively unique and distinct. But it can readily be
shown that these psychological fusions and compounds are elaborations of
more unitary experiences which have as their basis distinct mechanisms
in the nervous system and sense organs. For example, the sensation of
“heat” is a readily recognizable and identifiable experience, yet the
physiologist tells us that there is no separate sensory apparatus for
this impression. Cold and warmth, we are told, depend on the stimulation
of specific nerve endings. When these two types of endings, in the same
general region of the skin, are simultaneously stimulated, as the result
of the application of a stimulus with very high temperature, there
arises that new experience of “hot,” which is in this sense a
combination of warmth and cold.

Is it similarly possible to reduce to elementary units the rich manifold
of taste and flavor? If this can be done, in what way must such an
analysis proceed? What principles of classification are revealed, and
what and how numerous are the elementary taste qualities? The various
attempts that have been made to analyze the taste manifold are as
interesting as their results are instructive.


                     _The Classification of Tastes_

One method of classifying sense qualities that has often been advocated
uses as its basis the varieties of objects, agencies, or stimuli[2] by
the application of which the sense qualities are produced or aroused.
Thus the whole field of sense experience might be divided into thermal,
electrical, mechanical, photic (produced by light), etc. But such
sensations as are aroused by electrical stimuli, for example, may be
auditory, visual, cutaneous, gustatory (having to do with taste), etc.,
while these same varieties of sensory experiences may be aroused in some
cases by mechanical stimulation. Hence the classification of stimuli
does not yield an adequate analysis of modes of sensation. In the field
of taste this method, although it has been seriously attempted, is
equally futile. Thus various writers have attempted to group taste
sensations according to the species of plants and animals whose tissues
possessed sapid (taste-producing) qualities. It is obvious that this
method is unsatisfactory, since it is by no means true that all
specimens of a given vegetable taste alike. Even different parts of the
same plant have widely different tastes, and indeed the taste of a given
part varies widely with time and circumstances.

Footnote 2:

  By a “stimulus,” in this connection, is meant any object, force, or
  agent that acts upon a sense organ.

Even Chevreul, a famous early student of the sense of taste, adopted a
chemical classification, on the basis of the composition of the
substance tasted. Here again it is true that substances chemically very
dissimilar may possess tastes which are strikingly alike. Thus acetate
of lead, chloroform, and cane sugar, which, chemically considered, are
very dissimilar, may easily be mistaken for each other if their taste
alone is relied on; while starch, which is chemically closely related to
sugar, has no taste. It is also true that such different tastes as sweet
and bitter may characterize substances which are chemically very closely
related.

It is, however, true that certain broad lines of chemical classification
may be drawn. Thus those substances belonging to the colloid[3] group
are tasteless, the crystalloids all being sapid. When substances are
arranged according to the “periodic law” of chemistry, the elements
present in sweet-tasting substances are in general neither extremely
positive nor extremely negative. While it is the general rule that
soluble alkaloids are bitter, acids sour, sugars sweet, and salts salty,
there are many curious exceptions in every case. “It is true that we get
the taste of salt only from chemical salt; but there are chemical salts
that taste sweet, others that taste bitter, others again that have no
taste at all.” Similarly, while it is true that sour tastes belong to
acids, it is by no means true that all acids taste sour. Moreover, sugar
of lead, which is a salt, tastes sweet; while sulphate of magnesia and
other salts taste bitter.

Footnote 3:

  Resembling jelly or glue, uncrystalline in character.

Indeed, it is true that there are substances which have more than one
taste, the taste varying with the region of the tongue at which the
substance is applied. Thus saccharine, sulphate of magnesia, and acetate
of potassium are said to have sweet or acid taste if applied to the side
or tip of the tongue; whereas they are bitter if applied to the
posterior part. There are various other substances which show similar
changes in taste according to the point of their application. However
such facts may be explained, it is clear that the classification of
taste along chemical lines is not only beset with difficulties, but that
even in attempting such classification we resort to the use of a more
immediate classification, indicated by such words as sweet, sour, etc.

This resort to an immediately descriptive classification suggests that
the various taste experiences, regardless of the stimulus provoking
them, have certain similarities as direct experiences. This further
suggests that a strict psychological classification, based on the
attributes of tastes themselves, should be found through analysis. In
the case of sensations in general, such a type of classification is the
one that seems most satisfactory. Certain sense experiences, such as
red, yellow, orange, seem, as a matter of immediate experience, to
belong together and to be essentially different from such experiences as
warmth, tickle, noise, dizziness, etc. Furthermore, it is found possible
to pass by gradual steps of transition from red to yellow, through an
intervening orange, while there exists no such intermediate region
between red and tickle. As a matter of immediate experience, then, and
regardless of the nature of the stimulus, or, so far as we may be aware,
of the part of the body stimulated, certain sense experiences seem to
belong together, to constitute a certain _mode_ of sensation, such as
pressure, sound, etc.

Is it now possible to apply a similar test to the various _qualities_
which comprise the _mode_ or _sense_ of taste, and thus arrive at an
adequate classification and analysis of these qualities? The earliest
attempts to analyze the tastes by this psychological method were often
amusingly miscalculated. Thus Chatin, in 1880, presented a scheme in
which the total manifold of taste was first divided into agreeable
tastes and disagreeable tastes. The agreeable tastes were typified by
those we call sweet, and the disagreeable by those we call bitter. It
was, of course, at once necessary to indicate certain intermediate
conditions in this scheme for a variety of tastes which were neither
clearly agreeable nor markedly unpleasant. Moreover, it is a matter of
common experience that a taste which is agreeable to one person (such as
tobacco, olives, mustard) may be decidedly obnoxious to another person,
or, indeed, even to the same person on a different occasion; so that
such a classification cannot be said to represent in any fundamental way
an analysis of tastes.

There have been a great variety of classifications proposed on this
direct descriptive basis, and a comparison of the various schemes at
once suggests that the task is by no means as simple as it might seem.
The number of elementary tastes ranges widely, some investigators
enumerating five or six times as many fundamental taste qualities as
others have recognized.

Haller enumerated twelve different qualities—stale, sweet, bitter, sour,
sharp, tart, spicy, salt, urinous, putrid, spirituous, nauseating. It is
evident that this classification represents only a transition step
toward a psychological analysis and that it is by no means free from the
suggestion of provoking substances (spirituous, putrid) and the
suggestion of effects produced (nauseating).

Linnæus recognized somewhat fewer categories,—giving the following ten
as fundamental,—sweet, spicy, oily, mucous, salt, styptic,[4] bitter,
sour, aqueous, and dry.

Footnote 4:

  Styptic,—causing contraction of tissues.

Other authors have been content with indicating eight elementary tastes.
Both Bain and Wundt have proposed a sixfold classification, as
follows,—sweet, bitter, saline, alkaline, acid, and astringent or
metallic. Most modern authorities reduce the number of elementary tastes
to four,—sweet, salt, sour, bitter,—while at least three investigators
have advocated a simple twofold classification, into sweet and bitter.


                       _Taste Blends and Fusions_

These divergent accounts of the elementary taste qualities are in large
measure to be explained by the exceeding complexity of those experiences
which we in everyday life refer to as “tastes.” It was long ago shown
that a classification of the various senses on the basis of the gross
“sense organs” or parts of the body involved is as inadequate as one
based on the nature of the stimulating agent. The eye as a gross sense
organ yields experiences of pressure, pain, temperature, and strain, as
well as experiences of color and brightness. But these varied sensations
we recognize as belonging, as experiences, to quite distinct modes. Even
more complex are the varied sense experiences which we may receive
through stimulation of the tongue and the surrounding tissues. For the
tongue as an organ yields not only sensations of pure taste quality,
whatever these may be, but it also gives rise to experiences of pressure
with the varying characteristics of smooth, rough, moist, dry, contact,
tickle, etc.; to experiences of pain, with the ranging characteristics
and intensities, such as sting, smart, prick, burn; to experiences of
temperature, such as cold, warmth, heat; and to a vast complex of
kinæsthetic or muscular experiences of contraction, torsion, strain,
expansion.

In common experience these qualities of pressure, pain, temperature, and
kinæsthesis are scarcely discriminated from the purely gustatory or
taste qualities themselves. Thus we speak of “oily,” “fatty,” and
“greasy” tastes, in which the “smoothness” is certainly identical with
that felt by the fingers and other parts of the skin. Similarly the
pungent, astringent, puckering, biting “tastes” may come from substances
which have no taste at all in a strict sense, but which produce definite
smarting or stinging sensations when applied to the surface of the skin
or to exposed nerve endings (pepper, camphor). The puckering quality can
be shown by the characteristic muscular reaction to be largely
kinæsthetic and tactual in its origin. The difference in “taste” between
cold ice cream and the same substance when melted indicates how much of
the flavor is due to touch sensations and sensations of temperature. One
observer, indeed, reports the experience of four different qualities of
sensation from the stimulation of a single papilla,—a touch, a
temperature, a taste, and a pain sensation.

Further, many substances, in addition to these locally aroused
experiences of touch, temperature, pain, and movement, set up strong
organic reactions in more or less remote regions as well as strong
affective reactions: such as choking, nausea, and vomiting, on the one
hand, and extreme unpleasantness, disgust, distress, strain, and shock,
on the other. In many cases these immediate reactions seem to be reflex
or instinctive in their origin, and in other cases they seem to be
conditioned reactions, based on past experiences and associations. Thus
in one case the “taste” of ice cream, which was once agreeable enough,
has come to be immediately nauseating in character.

In spite of all these facts many of the classifications of taste
qualities have included the “oily,” the “nauseous,” the “astringent,”
etc., as primary taste experiences. Even if the complications we have
thus far alluded to were the only ones concerned, it would be clear
enough that the “tastes” and “flavors” of everyday conversation
represent very complex fusions and compounds, and that an analysis of
the true taste qualities, if such there be, must take these factors into
account in some very careful experimental way.

But we have left until this point a single complicating factor which in
itself is sufficiently serious to call for very careful technical
procedure in the examination of the sense of taste. This is the fact
that a very great number of our so-called tastes are not tastes at all,
but really odors. The sense organ of smell is so situated that it may be
stimulated not only in the ordinary way, through particles borne into
the nostrils by currents of air from the outside, but also by particles
and vapors which pass up, from the mouth cavity, behind the soft palate,
by way of passages called the “posterior nares.”

In this way it happens that tasteless substances, with definite odor,
are mistakenly supposed to have taste. In 1824 Chevreul reported a very
simple experiment with which his name has since been universally
associated. He pointed out that it is impossible to separate the action
of a substance on the touch corpuscles of the tongue from its action on
the taste buds themselves. He observed, however, that by a very simple
expedient it is possible to eliminate to some degree the factor of odor.
His classical experiment consisted in excluding the sense of smell in
large part by pressing the nostrils with the fingers while the substance
to be examined was presented to the tongue. In this manner he observed
that a piece of camphor gum which had seemed to have a very distinctive
taste had in reality no taste at all. When the nostrils were closed all
that could be observed as the result of placing camphor on the tongue
was a peculiar pricking sensation of touch, similar to that produced by
various other substances. The sensation produced by the camphor was thus
not a taste at all, but a fusion of odor and touch.

If, under the simple conditions of Chevreul’s experiment, the various
substances be reduced to a state of like consistency, so that they
cannot be recognized by the tactile sense, observers are usually much
amazed to discover that through taste alone it is impossible to
distinguish between quinine and coffee or between apple and onion. Many
familiar experiences of daily life testify to the large contribution
which the sense of smell makes to the supposed taste. How “tasteless”
are our fruits, wines, cigars, and vegetables when one has a cold in the
head, and the free passage of odorous particles to the organ of smell is
obstructed! How often has the nasty taste of medicine been softened by
Chevreul’s simple technic of “holding the nose”! There are some cases in
which the reverse of this situation occurs and volatile substances,
entering the mouth through the nostrils, stimulate the taste buds in the
upper and back part of the mouth. In such relatively rare cases the real
taste is mistakenly interpreted as an odor. In this way chloroform seems
to have the characteristic odor which is in all probability a sweet
taste due to stimulation of the taste buds by the chloroform vapor.

Why should it be the rule that, since the taste and smell qualities are
to be confused, smell should so commonly sacrifice its claim, so that
odors are called tastes rather than vice versa? No doubt this is true
largely because of the customary presence of sensations of pressure,
temperature, movement, and resistance which are localized in the mouth
and in the organ of taste. These accompanying sensations suggest that
the taste organs are active in determining the result, even when no true
taste qualities are present. It is common for sensations to be displaced
in some such way as this, just as the blind man, who is really getting
sensations from stimuli in the palm of his hand, seems to be getting
them at the end of his walking stick; or just as a faint sound may seem
to come from any source to which we direct our attention. Similarly, the
whole complex of touch, taste, and odor experienced as the result of
“sniffing” at a particular substance are quite likely to be credited
entirely to the sense of smell.


                         _The Poverty of Taste_

Here, then, is a most interesting situation, which has been described by
the use of two apt phrases: “the poverty of taste” and “the
self-sacrificing character of smell.” Our analysis has tended constantly
to rob the sense of taste of the richness which we ordinarily credit to
it. In fact, modern authorities agree that there are only four qualities
which can be truthfully classed as tastes, namely, sweet, salt, sour,
and bitter. What we took to be the taste manifold is really a meager
equipment of four qualities, with such variations of intensity and
combination as these may possess. Both the richness and the manifoldness
come from qualities of other senses, parading under the guise of taste.
Smell especially is prone to sacrifice its claim in favor of its
neighbor, and it is common indeed for us even to use taste names in
describing odors; we speak of “sweet odors” and “sour smells,” although
sweet and sour are primarily taste qualities. Smell, then, not only
entirely yields many of its qualities to the various “taste blends,” but
allows some of its own sensations to pass under taste names.

Patrick has reported extended observations in which he studied the taste
experiences of an anosmic,—a person who had lost the sense of smell. In
some of his experiments this woman, with two other women as control
subjects, after having been blindfolded, attempted to identify various
substances taken into the mouth. The general principles on which the
experiments were based are stated as follows: “In theory those
substances not recognized by any of the observers depend for their
recognition upon sensations of sight; those recognized by the normal
observers but not by the anosmic depend upon sensations of smell for
their recognition; while those recognized by all observers depend upon
either taste, touch, or muscle sensations.” It was further suggested
that those substances recognized by the anosmic but not by the normal
subjects would seem to depend in the main upon touch or muscle
sensations.

These experiments disclosed many curious and unexpected facts. Breads
and meats, butter, cream, olive oil, and various fruits and vegetables
could not be easily identified when only sight was excluded. One of the
women, a housekeeper of long experience, could not recognize raw turnip,
raw potato, boiled pumpkin, cranberry sauce, or fresh pear when she was
blindfolded.

Chicken, turkey, and quail were found to differ surprisingly little in
actual taste, especially if their characteristic texture, smoothness,
and other tactual qualities were eliminated or disguised. The various
values placed upon different meats, breads, etc., in the general esteem
would seem to depend in great measure on associated ideas and emotions,
rather than on their actual qualities for taste.

Especially interesting is the list of substances which were recognized
and correctly named by both of the normal women in these experiments,
but which the anosmic was unable to identify. Patrick enumerates
twenty-seven such common substances. Among them, by way of example, were
vanilla extract, pineapple syrup, banana, grape, quince, strawberry,
tea, chocolate, sour milk, kerosene, claret, rhubarb, onion, eggs, and
boiled turnips. The results suggest that these substances, although they
seem to have very characteristic tastes, are actually differentiated and
recognized on the basis of their olfactory rather than their gustatory
or tactual qualities.

One justification of this olfactory sacrifice is suggested by the fact
that biologically one of the most important functions performed by smell
is that of aiding in the discrimination of food. Through smell the
animals perceive at a distance a substance which may offer itself as
possible food. Biologically, the immediate guide to the acceptance or
refusal of food is the sense of taste. In so far as smell is in part a
subordinate servant in this matter, and hence becomes easily associated
with such reactions as “eating” or “not eating,” no injury is produced
through the occasional confusion of the two modes.

We have thus reduced the rich manifold of taste to the qualities of
sweet, salt, sour, and bitter,—four meager qualities as compared with
the numerous unanalyzable qualities of various of the other sensory
modes. We have now to show by what logic, through what technic, and on
the basis of what evidence, we are compelled to grant to taste four
qualities rather than two or twelve, and why the final grant consists of
these particular four rather than others.


            _Psychological Analysis of the Taste Qualities_

As Chatin long ago observed, “The three senses,—taste, touch, and
smell,—are so intimately combined that they seem to refuse to yield
themselves to minute analysis.” These associations seem to be even
stronger than those between the various taste qualities, of which Ladd
and Woodworth have remarked, “On the whole it appears as if the four
tastes were rather isolated from each other, each representing almost an
independent sense. There is much blending, to be sure, but the amount is
apparently no greater between one taste and another than between tastes
and odors.”

We may now fairly ask how these four qualities may be made to reveal
their elementary and independent character, once we have eliminated the
complicating factors introduced by the intrusion of qualities from other
senses.

The first appeal is to common observation and experience, according to
which the four taste qualities,—sweet, sour, salt, and bitter,—stand out
as conspicuous classes within which may be placed a great variety of
“taste blends.” Thus many substances, while having more or less
distinctive flavors, resemble each other in that unanalyzable quality
which we call sweetness. The only question here is whether or not we
should also include qualities other than these four as ultimate and
irreducible. If we refer back to the lists of tastes proposed, we find
that many of them are such as can be shown to be analyzable into one or
more of these four qualities, plus the intrusion of tactile, thermal,
kinæsthetic, and olfactory qualities. Such tastes as nauseating,
aqueous, astringent, styptic, putrid, etc., are easily ruled out on this
score alone. Introspectively, by simple experimental variation, or by
casual observation, the complex character of many of these tastes is
easily revealed, and when the non-gustatory components are eliminated
the residue falls readily under one or other of our four qualities.

These reductions are borne out by definite experiment. The tactile
(touch), thermal (temperature), and kinæsthetic (movement) factors are
kept constant and reduced to a minimum by applying minute amounts of
various solutions to single papillæ or very small regions of the tongue.
Smell may be, under these conditions, in great measure eliminated by
closing the nostrils with cotton or wax, and by letting the tongue be
somewhat advanced beyond its usual position. When these conditions are
observed, it is found that the main sense qualities experienced are
those of salt, sour, sweet, and bitter, along with such touch sensations
as may be unavoidable. Temperature may be eliminated by having the
solutions maintained at the temperature to which the tongue is already
adapted.

The evidence on this point is not absolutely consistent. Some observers,
for example, feel impelled to add metallic and alkaline to the group,
making six elementary qualities instead of four. Other observers,—most,
in fact,—are persuaded that the metallic and alkaline qualities
represent mixtures of the salt, sour, sweet, and bitter, along with
unavoidable sensations of touch and smell. Thus, by a suitable mixture
of strong solutions of salt and sweet substances, the alkaline taste may
be very well produced. “It has been suggested that the metallic taste is
due to the simultaneous development of salt and sour tastes. The failure
to produce exact alkaline and metallic tastes synthetically is in part
due to the difficulty of imitating the tactual and other sensations with
which they are bound up.” Still other observers are convinced by careful
elimination of smell sensation that the unique character of the alkaline
and metallic qualities is really a question of odor.

By the application of specific drugs to the organ of taste further
indications are secured that these four qualities, unanalyzable to
introspection, also function in relative independence. Thus, the juice
of gymnema leaves temporarily destroys the qualities of sweet and
bitter, while sensitiveness to sour and salt remains unimpaired. “The
true acid or sour taste may be separated from the astringent effect
which accompanies it by painting the tongue several times with a five to
ten per cent solution of cocaine. Cocaine first abolishes the sour
taste, and after several minutes begins to abolish the astringent action
of the acid solution. Later, the sour sensation begins to return, while
the astringent effect is still in abeyance, so that the application of
an acid solution at a certain stage during recovery enables the true
taste character of sour to be differentiated.” It is also reported that
when gymnemic acid and cocaine are applied to the tongue, the one
abolishes the sweet and the other the bitter, thus leaving the two other
tastes relatively unimpaired. Certain mixtures seem to paralyze both
sweet and bitter, but the former sooner than the latter.


                 _Distribution of the Taste Qualities_

To these four elementary tastes we are not equally sensitive on all
parts of the sense organ. Roughly speaking, sweet is best tasted at the
tip of the tongue, and many forms of candy are prepared so as to allow
as much as possible the employment of this part of the taste organ.
Bitter, on the other hand, is best tasted at the back or root of the
tongue, which explains why many substances do not taste bitter until we
have swallowed them. The edges of the tongue are most sensitive to sour,
while in adults the central area does not commonly yield taste qualities
at all. In children, however, the taste buds extend not only over the
whole surface of the tongue, but are also found in the walls of the
cheek, the palate, and even on the larynx and epiglottis. Titchener has
suggested that these facts may explain “the childish tendency to take
big mouthfuls.”

Attempts have been made to determine whether these elementary taste
qualities depend on separate taste buds or papillæ. Experiments show it
to be true that some points respond only to sweet, sour, etc. But there
are others which yield two or three or even all four qualities, while
some yield no taste at all. In one such experiment thirty-nine papillæ,
in a certain region, were separately stimulated by acid, sugar, salt,
and quinine. Of these thirty-nine, thirty-one responded to salt, and the
same number to sweet, twenty-nine to sour, twenty-one to bitter. Four
yielded no taste at all, one responded only to bitter, and one to sweet.
In another case of one hundred and twenty-five papillæ examined by
solutions of sugar, quinine, and tartaric acid, sixty gave sensations of
all three qualities (sweet, sour, bitter), twelve gave both sweet and
sour, twelve sour only, seven bitter and sour, four bitter and sweet,
and three sweet only. None of them seemed to give a bitter quality alone
and this seems to be the general rule.

It is of course difficult in these experiments to restrict the
application of the stimulus to single taste buds or even to single
papillæ. But these experiments, along with the effects of drugs which we
have already described, suggest that the taste buds are not all alike in
function, even though they seem quite similar so far as appearance and
structure are concerned.


                       _The Vocabulary of Taste_

Several investigators have been interested in the study of the taste
names found in different languages and communities. It has been
suggested that such a study might throw light on the order of
development of the various taste qualities.

Kiesow found that both children and adults quite commonly confused
bitter with salt and sour. Myers found, in studying the taste names of
primitive people in the region of the Torres Straits, that they had no
word for bitter. In some primitive languages the same word is used for
sweet and salt. When there is a word for salt it is usually some
derivative of the word for sea water. Salt and sour are also often
confused. In Polynesia, indeed, a single word is used in describing
salt, sour, and bitter tastes. This is analogous to the fact that in
primitive languages it is often found that the same word is used to
indicate blue and black.

Attempts to argue from these facts of vocabulary to facts of
sensitiveness and order of development are, of course, open to many
sources of error. As Myers points out, “The differences between sour and
bitter are considered less striking than their common unpalatability.”
It has often been pointed out that in our own language sweet is probably
the only taste word that had from its very origin a gustatory meaning.
In some languages even the word for sweet means literally “tasting
good.”

Vocabularies do not develop in order that structural and functional
facts may be recorded for the information of forthcoming scientists.
Words arise in response to the demands of practical life. It is
practically more important that some substances “taste good,” and others
“taste bad,” than that there are just four elementary taste qualities.
Hence for certain primitive circumstances two taste words are all that
are needed in ordinary conversation. It by no means follows from this
that the salt, sour, and bitter, which all fall in the “bad taste”
category, are not discriminable from one another by the taste organs of
the savage. It would be just as cogent to insist that, since we have
only one word for the taste of various sour things, all of these various
tastes must be indistinguishable to us.

Nor is the argument safe that those sense qualities for which specific
names exist must be more ancient than those qualities for which names
are borrowed. Many of our color names are not primarily color names at
all,—as violet, rose, olive, turquoise, lemon, straw, orange, and,
perhaps, pink and green. Red, blue, and yellow seem to be more
essentially color names. Yet, it is difficult to suppose that an
organism sensitive to red and yellow should not also be sensitive to
orange, which may be produced by a mixture of red and yellow light.

In the case of the odors, which we have every reason to believe are
extremely ancient sense qualities, we have in our own language almost no
exclusively olfactory names. Smells are designated by the objects with
which they are associated,—as lilac, lavender, musk; or names are
borrowed from other sensory modes, as sweet, sour, heavy; or still more
descriptive and perceptual names are used, such as fresh, flat, rancid,
foul, nauseating. Interesting as the vagaries of vocabulary may be, they
yield very little information concerning the primitiveness,
elementariness, sensitiveness, or distribution of the various taste
qualities.


------------------------------------------------------------------------



                               CHAPTER II

                     THE ORGANIZATION OF THE TASTES


               _System and Organization in Other Senses_


IN the case of some of the sensory modes it is possible to arrange the
various elementary qualities in a schema or graph, representing in a
diagrammatic way their relations to each other, the results of their
combination, their influence on each other, etc.

Thus, in the case of vision the conventional “color pyramid” expresses
the various relations between the different elementary colors and the
different degrees of brightness. Red, yellow, green, and blue occupy the
corners of the base of a double pyramid. The upper apex represents white
and the lower apex black. On the side between red and yellow are found
the various oranges which result from mixing red and yellow light in
varying proportions. On the remaining sides are represented the
combinations of yellow and green, green and blue, blue and red. Along
the vertical axis range the different grays. Cross sections of the
pyramid indicate, at different levels, the result of mixing the
different colors with these grays, thus yielding the tints and shades of
the colors. Along the base, the colors which are at the extreme ends of
any diagonal passing through the center are complementary,—they
neutralize each other when mixed and under other circumstances each
tends to induce the other by contrast. The visual manifold may thus be
adequately schematized on a three-dimensional figure.

In a similar way the various tones, in the case of hearing, may be
arranged along a one-dimensional line, which represents the tonal scale.
Is it possible to arrange in any such systematic way the elementary
taste qualities so as to indicate their relationship to each other?
Before suggesting such a diagram it will be well to have in mind just
what relationships the various taste qualities do as a matter of fact
display.


                     _Taste Mixtures and Compounds_

The testimony of daily experience would probably be at once that the
various elementary tastes may combine to produce new tastes of a more
complex or even of a unitary character. Thus, the taste of lemonade is
distinctive enough. Yet even casual observation suffices to show that
the sweet and the sour components have by no means lost their identity,
since each can be singled out in attention and recognized as the
familiar elementary quality. Red and blue may fuse to produce a violet
or a purple from which the original elements can by no means be singled
out and identified through direct inspection. But it seems to be the
rule that tastes do not behave in this way, although the demands of
daily experience do not readily lead us to discover the fact. “Think,
for instance,” writes Titchener, “of the flavor of a ripe peach. The
ethereal odor may be ruled out by holding the nose. The taste
components,—sweet, bitter, sour,—may be identified by special direction
of the attention upon them. The touch components—the softness and
stringiness of the pulp, the puckery feel of the sour—may be singled out
in the same way. Nevertheless, all these factors blend together so
intimately that it Is hard to give up one’s belief in a peculiar and
unanalyzable peach flavor. Indeed, some psychologists assert that this
resultant flavor exists; that in all such cases the concurrence of the
taste qualities gives rise to a new basic or fundamental taste, which
serves, so to say, as background to the separate components. There is,
however, no need to make any such assumption. It is a universal rule in
psychology that when sense qualities combine to form what is called a
perception, the result of their combination is not a sum but a system,
not a patchwork but a pattern.... Hence, just as it would be absurd to
say that the plan of the locomotive is a new bit of steel or the pattern
of the carpet a new bit of colored stuff, so is it wrong to say that the
peach character of a certain taste blend is a new taste quality.”

The mixture of stimuli provoking two taste qualities does not, then,
produce intermediate qualities such as the orange which results from the
mixture of red and yellow. Instead, in this case, the two qualities do
one of these three things: (a) they may remain separate and distinct;
(b) they may fluctuate individually and alternate with each other in
their appearance; (c) they may tend to neutralize each other. If the
stimuli are very intense, oscillation is the common result. If the
stimuli are weak, some degree of neutralization is reported to be the
rule. Only in one case, namely, the mixture of sweet and salt, does a
new taste seem to emerge, which does not resemble either of the original
qualities. Kiesow finds that such a mixture, in the case of weak
solutions, gives rise to a quality described as “flat,” “vapid,” or
“insipid,”—the alkaline taste which we have already considered.


             _Compensation, Antagonism, and Neutralization_

In the case of color, there may be found for every quality or mixture an
opposite quality or mixture which when combined with the former either
completely neutralizes it or at least reduces its intensity. Thus blue
and yellow, of the proper tones and proportion, cancel each other,
leaving only an experience of gray. So do a certain olive color and a
particular violet, a certain orange and a particular bluish-green, a
certain red and a particular green.

We have already suggested that in case of weak taste qualities a similar
effect is present. “With the low intensities there is in most cases a
partial compensation, which is least for sweet and sour, better for salt
and bitter, better still for sour and bitter, sour and salt, sweet and
bitter.” These facts are utilized in daily life in the countless
combinations of dressings, sauces, seasonings and condiments used in the
preparation of food. We take sugar with our tea, our coffee, our
chocolate, our strawberries, our grapefruit, and our lemon juice, and
realize that it to some degree counteracts or neutralizes the bitter or
the sour taste of these foods in their original form. “Salt corrects the
sweetness of an over-ripe melon.” In our salad dressings, sauces,
gravies, relishes, and bitters we find the means of reënforcing or
toning down the taste qualities to suit our own particular fancy.

In part, of course, these effects are not achieved through the mere
process of neutralization. The addition of touch qualities, such as the
pucker of vinegar, the sting of pepper, the bite of mustard, and the
burn of onion, plays its own part in the constitution of a flavor,
regardless of their compensating influence on the pure taste qualities.

In line with the fact that taste and odor are easily confused, and
contributing perhaps to this confusion, is the fact that tastes and
odors are related to each other through their antagonism, almost if not
quite as definitely as are the qualities within each of the separate
modes. Thus, the sickening odor of many medicines is somewhat palliated
if they are taken in fermented juices or with the sour acids of fresh
fruits. “Quinine, which tastes bitter and has no smell, is corrected by
essence of orange peel, which has an aromatic smell and no taste.”
Titchener pertinently remarks that these results may in part arise from
the simple process of distracting attention from an unpleasant item to a
more agreeable part of the experience. On the other hand, the special
effectiveness of the introduction of odors into the complex rather than
pleasant sights and sounds suggests that the results in the case of
taste and smell are not solely a matter of attention, but are in part,
at least, dependent on the essential relationships between the qualities
of these two modes of sensation. In the chapter on “The Evolution of
Taste” certain light is thrown on the closeness of these relationships
by our knowledge of the intimate biological connection between taste and
smell. In certain lower forms of animal life it is indeed quite
impossible to draw any clear line between these two features of “the
chemical sense.”

In general, then, although the facts of compensation, antagonism, and
complementariness are to be observed within the field of the taste
qualities, the relations disclosed are by no means as definite nor as
systematic as they are in the case of vision. For a given primary color
quality there exists only one other elementary quality which stands to
it in the relation of antagonist. But we have seen that in the cases of
both sour and bitter there is at least some degree of antagonism with
all three of the other qualities, while both sweet and salt antagonize
in some degree both sour and bitter. Moreover, at least the sour, the
bitter, and the sweet appear to show antagonistic relations to certain
qualities of smell.

In none of these cases has there been presented clear evidence showing
the ability of one quality to totally efface another, so that no taste
whatever is present. In the case of colors, however, the result of such
combinations in the right proportions may easily be a total absence of
color quality. It is true that occasional instances of such effects in
taste have been reported, but the general rule seems to be that the
extreme degree of neutralization leaves an experience which is
recognized as a taste, but which is described as “flat” or as “insipid.”
It is possible, of course, that this “insipid” taste quality is the
tactile and kinæsthetic residue of the total experience, much as the
“gray” which results from the combination of complementary colors may be
described as the brightness residue of the total momentary effect. But
in the latter case the residue would be distinctly “visual” although not
“color.” In the case of taste nothing corresponding to the “brightness”
of vision is recognized, and the residue as we have described it would
consequently belong to a different mode of sensation.


                          _Contrast Phenomena_

The phenomena known as contrast are very familiar sense experiences. Not
only is it true that in the fields of perception and feeling the tall,
the good, the wholesome, the fast, the daring, and the pleasant have
their qualities enhanced when they accompany or follow upon the
diminutive, the wicked, the foul, the slow, the cowardly, and the
disagreeable; in the case of more simple sense experiences also contrast
effects are often both immediate and striking. The apparent temperature
of the air or water varies with the conditions from which we emerge into
them. The sudden calm after a thunderstorm seems even more empty than
the same conditions in Indian summer. The palest complexion assumes a
moderate rosiness if green ribbons and fabrics are suitably arranged
about or near it. Even a pure gray strip of paper becomes a rich pink
line or a yellowish band when placed across a background of saturated
green or blue.

Daily experience entails many such instances of contrast in the case of
the taste qualities as well. A ripe apple may surprise us by its
unexpected sourness if we come to it direct from a box of bonbons.
Experiments designed to investigate the presence and character of taste
contrasts are especially interesting and their results are in many ways
curious. If, under proper experimental precautions, a salt solution is
applied to one side of the tongue and a drop of tasteless distilled
water is simultaneously applied to the other side, the tasteless water
is reported as sweetish. If, instead of the distilled water, one apply a
sugar solution of such weakness that its taste could not under ordinary
circumstances be recognized, the sweetness becomes clearly apparent.
Under the same circumstances a solution otherwise producing a weak
sensation of sweetness is reported as being “very sweet.” The salt
solution, that is to say, induces by contrast the quality of sweetness
in tasteless substances and enhances the degree of an otherwise weak
quality aroused at another region of the tongue.

In much the same way a sugar solution induces saltiness, or sourness, or
perhaps bitterness, according to the individual, the occasion, and the
circumstances. Sometimes the salt induces a sour instead of the sweet.
The bitter, however, seems unable to induce other qualities by contrast,
and is at least seldom induced by the other qualities.

In this as in other respects the bitter quality seems to show
idiosyncrasies. Thus, it is generally accepted that no papillæ are ever
sensitive only to bitter stimuli. Many primitive languages are said to
contain in their vocabulary no word for bitter: it is not uncommon in
daily experience to find bitter confused with sour; bitter seems to be
especially easily antagonized by certain odors; it does not display
striking contrast phenomena; and its reaction time is exceptionally
slow.

The type of contrast which we have thus described in the case of the
tastes is known as _simultaneous contrast_. Both stimuli are applied at
the same time to different parts of the sense organ. What is known as
_successive_ contrast can also be experimentally produced. Here one of
the stimuli follows the other after an interval in which nothing is
applied or, still better, in which the mouth is carefully rinsed with
water. This is the type of taste contrast with which we are most
familiar in daily life. The same contrasts may be induced experimentally
by this method as result from the simultaneous method. But the inducing
stimuli in this case must be rather more intense than is necessary for
the production of simultaneous contrasts. In much the same way in
perception as in sensation the contrast between two extremes or
opposites is better realized when both are present together than when
one follows the other after an interval.

The general facts of taste contrast are succinctly summarized by
Titchener in the following way:

(1) Salt and sour contrast: the sour induced by salt being clearer and
stronger than the salt induced by sour.

(2) Sweet and sour contrast: the sweet induced by sour being clearer and
stronger than the sour induced by sweet.

(3) Salt and sweet contrast: the sweet induced by salt being clearer and
stronger than the salt induced by sweet.

(4) Bitter shows no contrast at all.

(5) The order of qualities, as regards ease of induction, is sweet,
sour, salt, bitter.


                        _After Images of Taste_

Suggested by the phenomena of contrast are the somewhat related facts of
after sensations or after images, as they are sometimes called. When one
looks for a moment at a candle or other source of light and then quickly
extinguishes it or looks away from it, one still continues to see, for a
time, a luminous form, which may persist for a considerable time after
the removal of the stimulus. In such a case the color and brightness of
this after image may be the same as those of the original object, and
the after image is hence said to be _positive_. Under certain conditions
the colors of the after image are complementary to those of the original
and the brightness relations of the various parts are reversed. The
after image is then said to be _negative_. Or if after looking at a
colored object one transfers his gaze to a gray expanse there appears
upon this gray field an outline of the original object, with colors
which are complementary or antagonistic to those of the original. After
sensations of pressure arising under special conditions have been
described, and positive after effects of warm and cold stimuli seem also
to be demonstrable. Even after sensations of sound, somewhat weak,
transitory, and by no means easily detected, have been described. In all
these cases except vision the after sensations are of the positive type
only.

In the case of taste, and of smell also, it is difficult to investigate
the presence of such after sensations, inasmuch as it is by no means
easy to be sure that some trace of the stimulus does not remain in or
near the sense organ. An experience reported as a positive after
sensation might easily enough represent only the effect of persistent
stimulation by these traces of the substance. At least one investigator
is convinced that in his observations of taste experiences “the
sensation continued after the tongue was so carefully dried off that no
particles of the tastable substance were left.” Similarly, experiences
of tastes being “left in the mouth” are very common. But our inadequate
control over the disposition of the sapid substance and the complicated
chemical relation which exists between various substances and between
some substances and the natural juices secreted in the vicinity of the
taste organ makes it impossible to assert with certainty either the
presence or the absence of after sensations of taste.


                    _The Schema of Taste Relations_

The foregoing facts concerning the phenomena of mixture, fusion,
antagonism, contrast, and after sensation show at once the
impossibility, in our present state of knowledge, of arranging the taste
qualities in any such systematic scheme as is represented by the color
pyramid and the tonal scale in the cases of vision and hearing. It by no
means follows, however, that such orderly arrangements have not been
attempted.


[Illustration: Fig. 1.]


Kiesow, one of the most famous students of the sense of taste, proposed
that a circle with a vertical and a horizontal diameter indicated would
best represent the various relations between the taste qualities. At top
and bottom would stand salt and sweet; to left and right, bitter and
sour. Along the horizontal diameter would be placed the mixtures of
bitter and sour, and along the vertical diameter would range the various
results of mixing salt and sweet. The mixtures of salt-sour, sweet-sour,
bitter-sweet, and bitter-salt would stand in their appropriate places
about the circumference or periphery of the circle.

Wundt tentatively adopts a similar scheme when he says: “The system of
taste sensations is, accordingly, in all probability to be regarded as a
_two-dimensional_ continuity, which may be geometrically represented by
a rectangular surface at the angles of which the four primary qualities
are placed, the various mixed qualities being placed along the side and
on the inner surface.”

To such suggestions, however, Kuelpe objects that: “There is no
indication of a continuous transition between the four qualities which
tastes appear to present, as there is between the qualities of tone
sensations. They form, not a one-dimensional manifold, but a discrete
system of unknown relations.”

Titchener, one of the most careful students of sense experience, is less
emphatic, but he “doubts whether, in the present state of our knowledge,
this idea (that of Wundt) can be accepted.” He doubts “whether the
sweet-sour of lemonade stands to its originals as blue-green stands to
blue and green, or as orange to red and yellow; and also whether bitter
should lie in the same plane with the other three taste qualities. We
must suspend judgment; in the meantime, Kiesow’s figure provides us with
a working hypothesis.”

Ladd and Woodworth align themselves with Kuelpe and conclude that,
“there is no clear indication that the tastes can be arranged in a
linear scale, as the primary colors are, nor that any taste stands to
any other definitely in the relation of opposite or complementary. On
the whole it appears as if the four tastes were rather isolated from
each other, each representing almost an independent sense.”


------------------------------------------------------------------------



                              CHAPTER III

                       THE SENSITIVENESS OF TASTE


                  _Various Measures of Sensitiveness_


IN a general way it is well known that exceedingly weak solutions of
many substances are sufficient to provoke sensations of taste. It is
also known that weak tastes which some individuals are able to detect or
to recognize correctly go quite unobserved by others. The same thing is
true of differences between tastes. The connoisseur is sensitive to
minute differences in the flavor of wine, tobaccos, and sauces. Through
practice the expert taster of these substances acquires a skill which is
quite incomprehensible to the inexperienced. In part only is such skill
a matter of special sensory activity. It is in large measure a matter of
perception rather than one of sensation,—a knowledge of what signs to
look for and how to interpret these signs,—rather than an increased
sensitiveness to stimuli. In the same way the skilled gardener, hunter,
or scout is alert to the significance of particular signs and clues and
this alertness and apt interpretation may make him appear to have senses
of exceeding acuteness, although this may by no means be borne out by
actual measurements.

The psychological problems involved in the measurement of keenness of
taste are mainly two in number. One problem concerns itself with the
question, What is the faintest stimulus that can be sensed,—the weakest
taste that can be appreciated? The other concerns itself with the
sensitivity to difference between tastes, and would be expressed by some
such question as, How slight a change in the amount or intensity of the
stimulus is required for one to be able to perceive a change in the
intensity of the taste sensation?

Unfortunately for our knowledge of tastes, both these problems are very
difficult to approach experimentally. Whether or not a given weak
stimulus will provoke a taste sensation depends on very many things
other than the strength of the solution. The amount of solution applied,
the extent of surface excited, the duration of the application, the
temperature of the solution, the state of rest or movement of the sense
organ, and the nature of preceding stimuli, among other things, are
important.


                   _The Threshold of Taste Sensation_

Numerous investigations have concerned themselves with the task of
discovering the weakest solution of various substances that will provoke
their respective sensory qualities. The main results of these studies
have been the demonstration of two facts, namely, that exceedingly weak
stimuli may arouse sensations of taste and that this minimum solution
varies greatly in amount according to the substance which is in
question.

Valentin, in 1842, measured the lower threshold for solutions of sugar,
salt, quinine, and sulphuric acid and found the following proportions to
represent the least amounts able to arouse the corresponding sensation:

             Sugar    1.200 parts to 100 parts of water
             Salt     0.300
             Acid     0.001
             Quinine  0.003

Numerous other investigators have reported figures of this character.
Thus, Nichols and Bailey give the following as averages of the lower
thresholds in the case of measurements on forty-six women:

                Sugar    1 part to       204 parts water

                Salt     1 part to     2,000 parts water

                Acid     1 part to     3,300 parts water

                Bitter   1 part to         456,000 parts
                                                   water

It is neither profitable nor interesting to draw close comparisons
between the various sets of measures, since they vary considerably with
the substance used, and since, after all, as one writer remarks, “the
experiments are chiefly valuable as gratifying our curiosity.” Various
students of individual differences have sought to determine the presence
of sex differences, age differences, race and group differences, in
these minimal taste stimuli. But the incidental factors are so numerous
and so beyond experimental control that, if such differences exist, it
has never been possible consistently to demonstrate their nature or
amount.


               _Relative Sensitivity of Taste and Smell_

A recent investigation by Parker and Stabler was directed toward a
question which possesses a certain interest. Reasoning that, since taste
and smell are both “chemical” senses, it might be possible to compare
their respective sensitivities in terms of the strength of solution
required to affect them both, they attempted to make such comparison in
the case of one substance. Pure ethyl alcohol is a substance which has
both a distinctive taste and a distinctive odor. These investigators
found that the minimum amount of this substance that could be sensed by
taste was 24,000 times as great as the least amount that could be
detected by odor.


                     _The Discrimination of Tastes_

In the case of our second general question, that concerning the amount
of change in the strength of solution required to produce a felt
difference in the intensity of the taste sensation, various difficulties
are involved. In the first place, there is no known way of measuring the
intensity of that mode of stimulation which may be responsible for the
excitation of the taste bud. In such cases as the sensibility to weight
and light it is easily possible to measure the intensity of the stimulus
in terms of pounds, candle power, or similar physical units. In the
cases of temperature and sound the problem is much more difficult, since
we do not know precisely what aspect of the stimulus should be used as
indicating the intensity of the process at the point of stimulation.
Taste and smell offer still greater difficulties, inasmuch as we do not
know even with moderate certainty the real nature of the
stimulation,—whether, for example, it be mechanical or chemical, or
both. Consequently, although it is possible to state that in general a
change in the stimulus intensity required to produce a sensation change
which will be correctly reported in a certain percentage of the trials
is 1% for light, 33% for sound, 5% for lifted weights, no such
coefficients of change can even be suggested for taste and smell. Only
the general statement can be made that, within limits, increased
strength of solution means increased intensity of sensation.


                        _Adaptation and Fatigue_

Curious phenomena in the case of all the senses are those known as
adaptation and fatigue. It is a familiar experience that the
illumination of a room which seems upon entrance to be yellowish quickly
comes to appear merely light. After a few minutes wearing colored
goggles the tinge they give to objects seems to disappear and we say we
have become “adapted” to the color. “We become rapidly adapted to a
constant stimulus so that we fail to notice the weight of our hats, the
temperature of the room we are in, the odors of the subway.” Searching
for spectacles which meanwhile perch upon the nose is the result of
adaptation. A related phenomenon is the fact that a darkened room which
on entrance seems perfectly black comes in time to show its contents as
more or less clearly marked off from one another.

Some adjustment—in the sense organs, perhaps, or perhaps in the brain
centers—takes place in the presence of a constant stimulus. The general
result of this adjustment is that the particular sense quality involved
fades away: colors tend toward gray, pressures tend to disappear,
temperatures tend toward a neutral point, and sounds become indifferent.
This adjustment is not fatigue in the usual sense of the word. The area
that has become adapted to a given pressure is still sensitive and will
feel even a lighter weight if this be substituted for the one to which
it has become adapted. It is adapted to a continuous stimulus, but it is
sensitive to any change in the stimulus.

In the case of smell it is notorious that odors constantly present soon
cease to be observed or even to be observable. Even the most
disagreeable and insistent odors fade away in time. In a few minutes
stale cheese comes to have no discernible odor, while the odors of
tobacco smoke and various perfumes disappear equally quickly. In this
sense adaptation seems to be much more like exhaustion or fatigue than
in the cases of sound, sight, and pressure, and it may require a
considerable interval of freedom from the stimulus before the quality
returns.

The laws and effects of adaptation are by no means the same for all the
senses. Thus, in the case of smell, adaptation to certain odors seems to
increase our sensitivity to other odors. In the case of taste the
effects are by no means clear nor consistently reported by different
observers. In general it seems to be true that the effect of adaptation
to a given taste quality has no demonstrable effect on the remaining
qualities, and that this effect, as in the case of smell, is of the
general character of exhaustion. Taste, along with smell, seems to have
not yet developed any peripheral or central mechanism whereby adaptation
may take place without actual loss of sensibility.


                           _Acquired Tastes_

In a very different sense the word “adaptation” is often employed to
express the phenomenon of habituation in the case of “acquired tastes.”
Here the habituation is not to the taste quality, in a sensory sense,
but represents a change in the feeling or affective tone which
characterizes or accompanies this quality.

The easier case to understand is that in which the continued indulgence
in a substance, such as ice cream, candy, tobacco, sets up organic
effects which have their unpleasant accompaniment. Here it happens that
a taste originally very pleasant becomes indifferent or even disgusting.
The unpleasantness in such a case is rather easily seen to arise, not
from a taste quality alone, but from the total state of the moment. On a
later occasion the first appearance of the taste quality may, by
well-recognized associative mechanisms, arouse the organic revulsions or
memories of them, with the attendant disagreeable effect. The originally
agreeable taste then appears to have become disagreeable.

Cases of the reverse order are equally familiar, in which a taste
originally unpleasant comes, with repetition, to lose its disagreeable
character, or even to become distinctly pleasing. Indeed, in many such
cases habituation results in the establishment of a craving for the
quality which was originally repulsive. Here the repetition of the taste
quality seems to set up defensive adjustments and adaptations of a
profound organic kind rather than the earlier protective reactions of
refusal and rejection. Once this adjustment or adaptation takes place
the presence of the original stimulus is called for as part of the new
condition of balance, and the craving, or appetite, results. In this
account, it must be confessed, we speak in terms of vague generalities,
since it is not easy to state the precise nature of these biological
adaptations. But their existence in the case of many users of such
things as olives, garlic, tobacco, liquors, and various drugs is a
matter of common experience.


                    _The Early Development of Taste_

In the chapter on “The Evolution of Taste” it will be shown that very
early in the development of the forms of animal life there is present a
form of sensibility to that type of stimulation which, in our own
experience, provokes sensations of taste. The “chemical” sense is thus
seen to be a very primitive mode, and adjustments to chemical factors in
the environment are present at a very low level of organic development.
It is a general rule that capacities which appear thus early in the
animal series (phylogeny) also appear relatively early and relatively
complete in the development of the individual (ontogeny) of more
elaborate forms. So far as we are able to discover, this rule holds for
the development of the sense of taste. In a number of cases individual
infants have been carefully observed in order to note the order of
development of the various senses and the adjustments to stimuli in
these different modes. In several cases large numbers of newborn infants
have been tested immediately after birth, with the same questions in
mind.

These studies show that not only is sensibility to taste present at the
time of birth, but that the newborn infant reacts in different ways to
the various taste qualities. On the first experimental application of
taste stimuli distinguishable reactions, such as quiet sucking,
grimacing, nausea movements, facial expressions, and varied mimetic
behavior, indicate that at least in a rudimentary way the various taste
qualities are responded to in a selective or discriminative manner.

Thus, Kussmaul, in 1859, tested twenty-one children with solutions of
sugar and of sulphate of quinine. In general the sweet and the bitter
caused “the same mimetic facial movements as are observed in adults.”
There seemed, however, to be certain individual differences in
sensitivity, and occasionally sweet and bitter provoked facial reactions
which were not distinguishable. Guezer, in 1873, studied fifty newborn
infants by giving them tastes of sugar, quinine, and weak acetic acid.
The sugar, as a rule, produced “pleasurable sucking,” the quinine and
acid produced “unpleasant ‘bitter’ expression and even nausea
movements.” Kroner, in 1882, recorded studies of the taste reactions of
his own children at birth. He observed that they reacted immediately
after birth to sweet and bitter with the characteristic facial
expression of the adult. He was convinced that the sense of taste was at
birth the best developed of all the senses.

The most elaborate study of this kind yet recorded is that of Peterson
and Rainey. These observers report tests of 1,060 newborn infants,
varying in nationality, color, sex, and period of gestation. The
experiments included tests on all the senses. As taste stimuli for salt,
sour, sweet, and bitter they employed solutions of salt, acetic acid,
simple syrup, and tincture of gentian. The tests of taste showed “with
great regularity mimetic reactions to these stimuli characteristic of
adults, grimaces of discomfort, or expressions of content and liking.”
“The gustatory nerve not only reacts differently to salt, sweet, bitter,
and sour at birth, but the same mimetic reactions are observed in
premature infants. This nerve is therefore ready to receive taste
impressions some time before the normal period of birth.”


------------------------------------------------------------------------



                               CHAPTER IV

                   TIME RELATIONS OF TASTE QUALITIES


                   _The Inertia of the Taste Organs_


MANY experiments have been undertaken in the effort to measure the
inertia or sluggishness of the various senses. Inasmuch as the nervous
structure is a physical system set in operation by the incidence upon it
of external agencies, in each of its parts it requires a certain time in
order to be set going; and, once set in operation, acquires a certain
momentum which necessitates that a certain time elapse before it is
again in a state of equilibrium. At least the sense organs all show such
inertia, so that, in a given case, only a limited number of distinct
sensations can be produced in a given time by successive stimulation. A
measure that has often been used for expressing such facts is the
maximum number of separate excitations to which the sense organ responds
in a unit of time, as one second. This measure, to be sure, varies
considerably with numerous conditions and circumstances, such as the
nature of the stimulus, the part of the sense organ affected, its
previous condition, the intensity of the stimulation, etc. This measure,
which may be said roughly to indicate the duration of a sensation
(including its positive after image), is very short for touch, somewhat
longer for sound, and still longer for vision. Because of the nature of
the stimuli in taste and smell and the difficulty of accurately
controlling their application and removal, satisfactory measures of the
inertia of these sense organs have never been secured.


                    _Reaction Time to Taste Stimuli_

One fact, however, seems to be fairly clear from experiment, although it
would by no means be suspected from casual observation, namely, that the
various taste qualities are not equally prompt in the time required for
them to appear after the application of the stimulus. Salt and sweet
come rather quickly as compared with sour and bitter, the order of speed
being salt, sweet, sour, bitter. How much this may depend merely on such
differences as may exist in the structure and location of the various
taste buds it is impossible to say. Kiesow points out that taste
sensations are tardy and gradual in their appearance. If the person
being stimulated be required to indicate by a signal the instant at
which the taste quality appears, it is possible to measure, in very
small units of time, the interval between the superficial application of
the solution and the appearance of the sensation. This is called the
“reaction time” to the taste stimulus. When the stimuli were applied to
the tip of the tongue Kiesow found the following figures to represent
average reaction times to his different solutions:

                                      Seconds
                          ───────────────────
                          Salt           .307
                          Sweet          .446
                          Sour           .536
                          Bitter        1.082

The reaction to bitter, which requires twice as long in the above case
as that of any other quality, was considerably shorter when the stimulus
was applied to the root of the tongue. This suggests that the
differences found by Kiesow may in part, at least, depend on the
accessibility and perhaps also on the number of such various types of
taste buds as there may be.

Taking these reactions times as they stand, the average time for the
four taste qualities may be said to be about one-half a second. As
compared with the reaction times of other sense modes, taste is more
sluggish than any other sense, with the possible exception of smell.
Averaging the results of numerous observers for the range of stimulus
qualities and intensities that have been employed, the comparative times
are somewhat as follows:

                         Reaction to Second
                        ───────────────────────
                               sound  .146
                               touch  .149
                               sight  .189 (?)
                               smell  .500 (?)

It should, of course, be borne in mind that these are but averages of
figures which vary considerably with a large number of factors, although
it is true that the influence of these factors can itself be subjected
to precise measurement.


                _Determinants of Reaction Time to Taste_

By way of illustration of the numerous incidental and extraneous factors
that influence reaction time to the taste qualities we may instance the
temperature of the solution. In what seems to have been a carefully
conducted series of observations Chinaglea has recently shown the nature
of this influence. As Kiesow had already found, the temperature of the
solution (within the pain limits) does not influence the intensity of
stimulus required to produce the weakest sensation, and hence does not
modify the threshold or limen. But such changes Chinaglea showed to have
a measurable influence on the reaction time to taste stimuli. Lowering
the temperature of the solution below that of the mouth does not affect
reaction time to salt, but it lengthens the time for the other
qualities. Raising the temperature of the solution above that of the
mouth quickens the reaction to sweet, but lengthens the reaction to
bitter and sour.


------------------------------------------------------------------------



                               CHAPTER V

                        THE SENSE ORGAN OF TASTE


                  _Comparison With Other Sense Organs_


THE so-called higher senses are usually differentiated from the lower on
the basis of their greater intellectual value. The sense of taste is one
of the lower, as compared with vision and hearing, which are of the
higher group. Not only in the purpose which they serve, but also in the
character of their mechanism, do the senses differ. The sense of taste
differs from the sense of sight in at least three respects. First, it is
a mechanism not given over exclusively to the taste function, but serves
other functions as well. The visual mechanism, for instance, is very
highly specialized. It consists of an elaborate mechanical
device,—extrinsic and intrinsic muscles, lens, iris, etc.,—which serves
to prepare the physical stimulus to act upon the real receptor portion
of the sense organ, the retina. None of these parts of the eye serve any
other purpose than that of vision. In the case of the taste mechanism,
on the other hand, only the receptor[5] portion of the mechanism is
concerned exclusively in the taste function. The tongue, usually
considered the most important part of the taste organ, with its great
variety of movements, is a very necessary part of the speech mechanism.
The salivary glands, which by their secretions put the substances
entering the mouth into such condition that they may act upon the
receptor mechanism, are of vital importance for the process of
digestion. The small receptors imbedded within the coverings of the
tongue and the linings of the mouth cavity may be considered as the only
structures which perform exclusively a taste function.

Footnote 5:

  A receptor is the part of the sense organ in which the transformation
  from a physical stimulus to a nerve impulse occurs.

Secondly, it is not easy to determine the limits of distribution of the
receptor organs of taste, as one can do in the case of the eye, with its
clearly defined retina, or the ear, with its organ of Corti, or even the
nose, with its regio olfactoria (patch of mucous membrane). That is,
there is no one organ with its attachments which can be called the taste
organ. Consequently, one does not find any general agreement as to what
structures ought to be included in the taste mechanism. For instance, it
is well known that the taste function is not limited to the tongue, and
that the whole mouth cavity is a more or less important part of the
taste mechanism. Certain investigators are not willing to circumscribe
the taste organ within such narrow limits, but extend it to the larynx,
the vocal cords, and some have even gone so far as to include the
membranes of the nasal cavity.

Finally, the taste mechanism is extremely simple when compared with the
so-called higher senses, especially that portion of it whose function is
to prepare the stimuli to act upon the receiving mechanism. The taste
organ is generally believed to represent a stage in evolution very near
to the original structures from which all of the sense organs have
developed. That is, looked at from the evolutionary point of view, it is
a more primitive and less highly developed mechanism.


                _The Salivary Glands and Their Activity_

Consider first those portions of the taste organ which perform the
mechanical function of preparing the stimulus to act upon the receiving
mechanism or the sensory ends of taste. Most important of these are the
salivary glands and the tongue. The latter through its movements
facilitates contact of the taste substances with the sensory ends of
taste, and the former secrete saliva, which dissolves the sapid
substances, reducing them to the liquid form necessary for arousing
taste sensations.

The salivary glands and their secretions are of interest to the student
of taste only in so far as their activity forms a necessary step in the
taste process. In this connection it must be remembered that the chief
function of the saliva is the part it plays in the process of digestion.
As suggested above, the function of the saliva in the taste process is
merely that of dissolving or transforming solids into liquid form.
Consequently, the chemical constitution of the saliva and the detailed
structure of the glands are aside from our interest. The action of these
glands, three in number, and called the parotid, the submaxillary, and
the sublingual, is of the reflex type. The stimuli for the reflex are
numerous, and, it appears, are not the same for all of the glands. For
instance, the submaxillary glands are said to secrete upon the presence
of certain foods, acids in the mouth, the chewing of meats, etc. On the
other hand, the stimulus for the parotid gland has been shown by Pavlow
to be the presence of dry substances in the mouth. If no distinction is
made between glands, it may be said that watery foods cause only a
slight flow of saliva, while dry foods cause a large flow of saliva. One
sees, then, a set of reflexes which not only promote the digestion of
foods, but which also tend to make them tastable. These two functions
are not entirely separate ones, for it has been shown by experiment that
the tastes of various foods are determining factors in causing and
regulating the flow of gastric juice in the stomach.

Although the action of the glands is reflex in character, and is due to
the stimulation, by objects in the mouth, of the glossopharyngeal and
lingual nerves supplying the mouth and tongue, this is not the only
means by which the reflex can be excited, or the flow of saliva
produced. It is a matter of common knowledge that the _sight_ of various
objects—a lemon, for instance—will cause a copious flow of saliva, and,
further, that certain mental states, such as fear, anxiety, and the
like, may cause reduction of the flow of saliva, with the resultant dry
mouth, the cleaving of the tongue to the roof of the mouth, and other
unpleasant effects of lack of saliva. These last forms of activity must
be due to impulses coming to the glands or to the secretion center in
the brain stem from the cortical regions of the brain, and they are
called psychic reflexes or conditioned reflexes. That is, the reflexes
are conditioned upon the experience of the individual somewhat as
follows: If the visual experience of a lemon is followed a number of
times by the taste of the lemon and the reflex excitation of the
salivary glands from the presence of the acid in the mouth, it may come
about that the sight of the lemon unaccompanied by its entrance into the
mouth will cause the flow of saliva. The stimulus to the reflex activity
has changed from one of contact of a substance with the mucous membrane
of the mouth to a visual stimulus. As a result of the development of
these psychic or conditioned reflexes, if one sees a certain kind of
substance that he is going to taste, the flow of saliva necessary to
reduce it to a tastable form is brought about even before the substance
has entered the mouth. Pavlow cites a case in which a handful of clean
stones placed in the mouth of a dog produces a very slight flow of
saliva, while the same material in the form of fine sand causes a
copious flow of saliva. Such cases as this indicate the great delicacy
with which the salivary secretion is adapted to the condition of the
substances entering the mouth. No sapid particles entering the mouth dry
can stimulate the taste mechanism except through the mediation of the
saliva.


            _The Tongue: Its Muscles and Covering Membranes_

Considered as a part of the taste mechanism, the tongue is a body of
irregular shape, occupying a large portion of the mouth cavity. It is
composed largely of muscles, covered with a mucous membrane very similar
to that which lines the whole mouth cavity. It has an upper, or superior
surface, a lower, or inferior surface, two sides, and a tip, in addition
to the base, or region of its fixation. The muscles are of interest in
that they give to the tongue its great variety of movements, and the
membrane-covered surfaces are of especial interest, because in them are
found by far the greatest number of the nerve endings or the sensory
ends of taste.

The tongue is made up of seventeen muscles, acting in three
planes—vertical, longitudinal, and transverse. Separating these muscles
one from another are layers of fatty tissue, enabling the muscles to
glide easily over each other. Fifteen of these muscles are extrinsic in
the sense that one end of each has its point of attachment outside of
the tongue. It is these muscles especially that give the tongue its
great motility. By the contraction of single muscles or contraction in
various combinations the tongue is protruded or drawn back, the tip
raised or lowered, the dorsal surface pressed against the roof of the
mouth or withdrawn toward the floor of the mouth, the tongue protruded
and turned to one side or the other. In addition to these extrinsic
muscles there is a pair of intrinsic muscles, each having both points of
attachment within the tongue. By their contraction the sides of the
tongue are raised and drawn together.

These muscles are richly supplied with blood vessels and receive an
especially large supply of nerve fibers from the hypoglossal, which is
known as the motor nerve of the tongue, and some from the lingual branch
of the seventh, or facial, nerve.

It is generally believed that the tongue movements serve the sense of
taste only as they facilitate contact of the sapid substances with the
real taste endings; for instance, by pressure of the tongue against the
roof of the mouth, and by its protrusion from the mouth to receive the
stimuli upon its surface. However, it has been asserted by some
investigators that the movements are of more direct use in the taste
process, in that tongue movements in themselves tend to increase the
sensitivity of the taste mechanism. But careful experiments in which the
tongue was rendered motionless during tasting show that taste
sensitivity is just as great as when the tongue is free to move.

By far the most important portion of the tongue is its mucous covering.
This varies considerably in character in different regions, being
thickest and toughest on the superior surface where It comes into
contact with objects taken into the mouth, and thinnest on the inferior
surface where it is ordinarily protected from such contact. On the sides
and tip it is moderately thick and tough. The tongue covering has a
highly complex structure. Two distinct layers, or strata, are commonly
described: the more superficial, or epithelial layer, and the deeper
layer, called the chorion. The first, or epithelial, layer contains all
of the sensory endings concerned in taste upon the tongue, and these
will be described later. The second is more complex and consists of
connective tissue, a great network of blood vessels, nerve fibers, and
numerous glands and their ducts which open upon the surface of the
tongue. Upon the more superficial surface of this inner layer there is
an extremely large number of slight elevations. These are apparent to
the unaided eye upon the tongue surface, since the epithelial layer of
the membrane follows very closely the contour of this deeper layer.
These elevations are called papillæ. (Fig. 2.) They vary in size and
shape and are quite unevenly distributed upon the surface of the tongue.
On the inferior surface there are none, while on the superior surface
they are most numerous. With the aid of the papillæ on this surface the
tongue can be divided into two parts, an anterior or horizontal portion
and a posterior or vertical portion. The former includes about the
forward two-thirds of the tongue and the latter the posterior third.
These two parts are separated by a row of relatively large elevations,
about ten or twelve in number, and arranged in the shape of a V, with
the open portion of the V turned forward. From the apex of the V a
furrow passes forward to the tip of the tongue, dividing the anterior
portion laterally into two halves. The posterior portion is broken up
into a series of folds taking about the same direction as the legs of
the V.


[Illustration: Fig. 2.]


                      _Classification of Papillæ_

The papillæ of the tongue have been described and classified more or
less in detail since the middle of the seventeenth century. They can be
grouped into four classes (Fig. 2.), the circumvallate, the fungiform,
the filiform, and the foliate papillæ, each group having certain
distinctive characters. A fifth group is sometimes added and comprises
the hemispherical, or simple, papillæ.

The circumvallate group comprise the largest and the most important
papillæ. There are only from eight to twelve or sixteen of this type,
and by their arrangement they form the V-shaped figure on the superior
surface of the tongue, mentioned above, and which divides the anterior
two-thirds from the posterior third of the tongue. These papillæ are
found nowhere else. They rise only slightly above the surface of the
tongue from the bottom of a pit or cup-shaped depression, giving the
impression of a small mound surrounded by a ditch, whence the name,
circumvallate. In a few cases more than one papilla rises from a single
pit, but in most cases there is but one. The papilla itself has an
average height of 2 millimeters, with a diameter at the top of 1.0 to
1.5 millimeters, and slightly less at the base. The cup-shaped
depression averages about 1 to 1.5 millimeters in depth. The largest of
these papillæ is that one forming the apex of the V-shaped figure and is
called the foramen cæcum. The smallest are those found at the ends of
the V.

The fungiform papillæ are so called on account of their resemblance to a
toadstool. Each consists of a rather slender stalk capped by a
relatively large, rounded head, about .8 to 1.0 millimeter in diameter.
The whole papilla has an average height ranging from 1.0 to 1.5
millimeters. These are scattered very irregularly over the superior
surface of the tongue, most of them being found on its anterior
two-thirds. However, a few are found back of the circumvallate papillæ,
but always very close to them. They are most numerous on the sides and
the tip of the tongue, where they appear as bright red points upon the
paler background of the tongue covering. The total number of this type
has been estimated at from 150 to 200.

The third type, the filiform papillæ, cover the whole superior surface
of the tongue and are so numerous that no estimation of their total
number has been made. They are arranged in fairly regular lines running
to each side from the middle line of the tongue and parallel to the
lines formed by the circumvallate papillæ. They are believed to contain
no sensory ends of taste and have only a mechanical function, if any, in
connection with the taste mechanism. They are conical or cylindrical in
form and vary in height from 1.5 to 2.5 millimeters. Sometimes these
papillæ are covered with tiny secondary papillæ, which, however, are not
apparent to the unaided eye.

The foliate papillæ consist of numerous small folds of the membranous
covering of the tongue upon its sides and just in front of the line
formed by the circumvallate papillæ. In these folds a large number of
the taste bodies are imbedded. In certain animals, especially the
rodents, these foliate papillæ form a very prominent part of the tongue,
while in man they are no more prominent than the other forms.

The hemispherical, or simple, papillæ are found distributed over the
whole tongue surface and form in many cases secondary papillæ upon the
larger fungiform and circumvallate type.

The papillæ of these different types contain the largest number of the
sensory ends of taste, or the taste bodies. These structures will be
discussed in detail later. They are most numerous in the circumvallate
papillæ, where one may find hundreds imbedded in the side walls of one
papilla. They are also found in the side walls of the depression from
which the papilla rises. The fungiform type also contain these taste
bodies imbedded in their side walls, although there are some in which
none have been discovered. According to Nagel, the taste bodies have
never been found in the filiform type. He ventures the opinion that the
taste bodies are not necessary to produce taste sensations, with the
result that the filiform papillæ may, after all, have something to do
with taste sensations. There is always the possibility, first suggested
about 1870, that the free nerve endings in the tongue surface may give
rise to taste sensations.


                 _The Determination of the Taste Areas_

How shall the limits of the taste mechanism be determined? Two methods
have been employed, and usually in conjunction. The first, or the
anatomical method, consists in searching for the taste bodies (to be
described later), and when they are found, to assume the possibility of
taste sensations from the stimulation of that region. The second, or the
physiological method, consists in applying stimuli of various sorts to
different regions and finding whether taste sensations result. The
limits of the taste mechanism, when determined by these two methods
taken separately, do not always agree. But there are cases in which only
one or the other method taken alone can be applied. For instance, in the
case of the embryo it is clear that only the anatomical method can be
used, and in the case of the living human being only the physiological,
or stimulation, method can be used.

The discrepancy between structure and function is possibly due, in part,
to the presence of functionless taste bodies, useless landmarks in
regions where in earlier stages of evolution the taste function may have
been of vital importance. Such an explanation has been offered for the
presence of taste buds upon the upper surface of the soft palate and
upon the walls of the larynx and the vocal cords. But there are at least
two other causes for the differences in limits of the taste sense as
determined by the different experimenters,—careless and imperfect
technic of experimentation and the great individual differences,
according to age, race, and other conditions. Just on account of these
individual differences it is impossible to define the limits of the
taste sense which shall hold for all persons; one can only give averages
and avoid the exceptions. Taking the average adult as tested by the two
methods, one can say that the taste mechanism includes the following:

1. The superior, or upper, surface of the tongue, with the exception of
a patch just back of the tip. The size of this patch, which is
insensitive to all taste stimuli, varies considerably with the kind of
stimulus used and its intensity.

2. The sides and tip of the tongue. The under surface of the tongue of
human beings is said to be insensitive to taste.

3. The soft palate, the uvula, and the tonsils, although the extent of
these parts that is sensitive is subject to considerable variation.
Kiesow and others fail to find the uvula sensitive at all.

4. The gums, the hard palate, and the mucous membrane of the lips are
generally considered to be insensitive to taste. This absence of taste
sensitiveness upon the hard palate, or roof of the mouth, is interesting
when one considers its close connection with taste in popular speech. To
“tickle the palate” with delicious food, to make food “palatable,” are
very common, though misleading, expressions. However, two very careful
investigators have reported that the lining of the whole mouth cavity,
including gums, the lining of the cheeks, the hard palate, and even the
teeth, are sensitive to sour stimuli. Acetic acid of full strength was
used as a stimulus in these experiments.

5. The epiglottis, parts of the larynx, and the vocal cords are
sensitive to taste stimuli. Not only have the taste bodies been
discovered in these parts, but certain investigators, by applying
solutions of bitter, sweet, etc., have been able to elicit the
corresponding sensations from these parts. To these taste organs have
been attributed the tastes aroused by certain vapors, such as
chloroform, ether, etc.

6. The regio olfactoria, or the olfactory membrane, has been said to
give rise to taste sensations, and the question has aroused much
dispute. The evidence for thus attributing taste to the smell mechanism
consists in the discovery in the regio olfactoria of bodies similar to
taste bodies, and the further fact that breathing chloroform through the
nose gives rise to a stinging sensation, followed by a sweet taste.
Introspection seems to localize this taste in the nostrils. Nagel,
however, denied the existence of this so-called “nasal taste” and
performed a simple experiment to prove his contention. He finds that if
one allows chloroform or ether vapor to be blown into his nostrils he
will get a burning sensation, followed in the first case by a sweet
taste and in the second by a bitter taste. But if while the vapor is
entering the nostrils the person constantly utters a vowel sound, thus
closing the passage between the nasal and mouth cavity, the sweet and
bitter tastes will disappear, while the burning sensation remains. Nagel
holds that this shows that the taste sensations must be due to the
stimulation of parts other than the nasal cavity. The same conclusion
has been reached by the more careful researches of Nagel’s students and
others upon individuals whose nasal cavity and mouth cavity have been
effectually separated either by growths or by artificial means.

One conclusion seems generally supported by the investigations of the
distribution of taste, namely, that one cannot assert positively that
wherever tastes have been definitely aroused there taste organs will be
discoverable, or the converse of this, that wherever taste buds are
found there taste sensations can always be aroused.


------------------------------------------------------------------------



                               CHAPTER VI

                SENSORY ELEMENTS OF THE TASTE MECHANISM


             _Taste Buds and Their General Characteristics_


EACH sense mechanism has an arrangement more or less mechanical for
modifying the stimulus, and another mechanism which transforms the
stimulus into the nerve impulse, that message which is carried from
sense organ to brain and there gives rise to consciousness. We know very
little about the real nature of this nerve impulse transmitted from
sense organ to brain, aside from its speed and a number of conditions
affecting it. Some call it a chemical phenomenon, others an electrical
phenomenon, and still others an electrochemical or physicochemical one.
We know even less—in fact, nothing—about the change from nerve impulse
to consciousness. But there are certain facts fairly well determined by
microscopical examination of the sense organ about the nature of the
mechanism which transforms the physical stimulus into a physiological
one. In the preceding chapter the more mechanical features of the taste
mechanism have been reviewed, and in this one we will describe the
transforming mechanism.

About 1865 it was found that the coverings of the tongue of mammals and
later the lining of the mouth cavity contained peculiar little bodies,
which, on account of their apparent shape and their connection with the
sense of taste, were called taste beakers. Small fissures called taste
pores were discovered among the most superficial epithelial cells of the
mucous membrane of the tongue, and these were thought to lead into the
small, flask-like chambers. Further study showed that the beakers were
not in reality hollow, but consisted of closely packed groups of
modified epithelial cells. They were then given the name of taste buds,
on account of their resemblance to a bud with its tightly folded petals.
These have been spoken of frequently in the preceding pages as sensory
ends, and the regions in which they are found were enumerated.

Each taste bud is set rather deeply in the epithelial layer of the
mucous membrane covering the sides of the papillæ and communicates with
the surface only by the above-mentioned taste pore. Thus the taste bud
is projected from direct stimulation by all substances except those
which can gain access through the narrow opening. Occasionally taste
buds are found which lack this gustatory pore and communicate directly
with the tongue surface. Such cases, however, are to be considered as
exceptions. Likewise, twin taste buds are sometimes found, having a
common base, but with peripheral ends distinct. These, too, are merely
exceptions to the ordinary form and do not represent a type. The taste
buds are globular in shape, measuring about 70 to 80 thousandths of a
millimeter in length and about 50 thousandths of a millimeter in
diameter. The taste pore averages only about 4 thousandths of a
millimeter in diameter.


        _Supporting Cells, Gustatory Cells, and Nerve Filaments_

A microscopical examination of the taste bud shows it to be composed of
three structures. First, there is a series of modified epithelial cells
closely packed side by side and forming a kind of hollow shell and
determining the limits of the taste bud. These are sometimes called
marginal, or supporting, cells. They are very long and narrow and their
thickest part is that occupied by the relatively large nucleus. The
extremities of the cells directed toward the taste pore are quite long
and thin and are gathered together so as to form a small circular
opening, the neck of the taste beaker or bud. Within this hollow globe
thus formed some of the same kind of cells are found, but it is almost
entirely occupied by the second type of structure, the taste cell. These
ordinarily range in number from 10 to 16 within any one bud, but
sometimes as few as two or three have been found. These cells are longer
and even more slender than the supporting cells and are very closely
packed. The peripheral portion of the cell is very much elongated and
ends in a hair-like filament which extends into the taste pore. All of
these hair-like endings of the taste cells gather into a kind of brush
within the taste pore. The centrally directed ends of these cells may
have various forms—that is, there may be one long, thin branch or a
number of branches, none of which, however, pass beyond the limits of
the taste bud.

The third kind of structure found in a taste bud is perhaps the most
important and consists of the fine branches of nerves which enter the
taste bud at its base and twine around the taste cells. They do not
actually grow into the cells, but pass through the taste bud and end
very near to the taste pore in the form of small knobs or knots. Some of
the fibrils, after reaching the peripheral end of the bud, turn back and
really end in the more central portions of the bud.


         _Relations Among the Structures Within the Taste Bud_

A great deal of experimental work has been done to determine the
relations among these three parts of the taste bud. It was at one time
thought that the supporting cells were modified epithelial cells and
only served as a structural support for the taste cells, which were real
nerve cells. According to this view, the taste cell is a neurone[6]
which is directly affected by the stimulus and forms the first link in
the chain of neurones connecting the surface of the body with the brain.
They were thought to be analogous to the olfactory cells, which are true
nerve cells. But a number of facts more recently determined tend to
minimize the distinction between supporting cells and taste cells. For
instance, when certain stains are employed for isolating the different
structures it is found that these two sorts of cells stain alike, while
the nerve fibrils within the buds stain differently from them. This is
taken as good evidence that there is a difference in the composition of
the taste cells and the nerve fibrils, and a likeness between the taste
and the supporting cells. In fact, both types of cells are now
considered to be modified epithelial cells and to be, in a sense,
supporting cells. The former serve as supports for the very delicate
nerve fibrils as they pass through the taste bud, and the latter, in
addition to acting as supports in this way, also form the walls of the
taste bud and thus protect the nerve fibrils from undue compression.
According to this view, then, the nerve fibrils themselves are directly
affected by the stimuli. Their knob-like endings, which are found so
closely associated with the taste pore in most cases, lend support to
this view.

Footnote 6:

  Neurone is the name given to a nerve cell, and includes the cell body
  with its nucleus, and all of its branches.

One further sort of evidence tends to show the merely secondary function
of these two types of cells in the taste bud. Certain portions of the
tongue, e.g., parts of the tip and sides, which are extremely sensitive
to taste stimuli, have very few taste buds, or none at all. But there is
a multitude of free nerve endings in these parts which are thought to
function without the aid of the supporting, or taste, cells. It will be
recalled that in Chapter V it was necessary to conclude that there
seemed to be no absolute dependence of taste sensations upon the
presence of taste buds.


                     _The Sensory Nerves of Taste_

The taste sense differs from most of the other special senses in a
number of respects, some of which have been mentioned in the preceding
chapter. Still another striking difference is to be found in the nerve
supply for taste as compared with that of the senses of sight, hearing,
and smell. In the latter group there is one nerve which carries the
impulses from the sense organ to the brain. Thus, we have the optic
nerve for vision, the auditory nerve for hearing, and the olfactory
nerve for smell. In taste, however, no single cranial nerve can be
called the nerve of taste or the gustatory nerve. There has always been
a great deal of difference of opinion as to how the taste fibers are
carried to the brain, no small part of which has been due to the seeming
necessity for finding “a taste nerve.” As early as 1823 evidence began
to accumulate to show that more than one nerve must be involved. Other
contributing factors to this confusion are, first, the use of
experimentation upon animals—the conclusions from which have been
considered valid for man as well as animals, an assumption which is not
necessarily correct; and, second, the fact that there seem to be rather
pronounced individual differences in the course taken by the fibers from
taste bud to brain center. Three of the cranial nerves are now generally
conceded to carry taste fibers: the lingual, which is a branch of the
trigeminus, or fifth, nerve; the glossopharyngeal, or the ninth, nerve,
and the vagus, or the tenth, nerve. The first two of these are more
important for taste than the third. The lingual carries the fibers from
the anterior two-thirds of the tongue, the upper surface, and the sides
of that portion of the tongue and the tip; the glossopharyngeal carries
the fibers from the posterior third of the tongue, including the base of
the tongue, the soft palate, and the papillæ foliatæ; the vagus carries
fibers from the epiglottis and the larynx.

Although the above facts are well established, the more important
question is, What is the origin of these fibers and how do they get into
the nerve trunks in which they are found? To make this matter clear a
word must be said about the general nature of sensory nerve paths. The
connection between a sense organ and the brain consists of a series of
separate links, which always remain distinct units. Each cell, or
neurone, as one of these units is called, consists of a body, which
contains the nucleus, and two sets of branches. In one set the branches
are very short and numerous, called dendrites; in the other there is
usually only one branch, called the axone, which is relatively long. A
group of cell bodies is called a ganglion. In practically all sensory
nerves these ganglia are situated outside of the central nervous system.
The ganglia of the spinal nerves are located just outside of the spinal
cord and are called simply spinal ganglia. The ganglia of the cranial
nerves usually receive special names. Thus, the ganglion for the great
trigeminal, or fifth, nerve is called the gasserian ganglion. Of the two
for the glossopharyngeal, or ninth, nerve that one of interest to us is
called the petrosal ganglion. The vagus has two ganglia, an upper and a
lower; the former, or jugular, ganglion is involved in the sense of
taste.

From these ganglia the branches called the dendrites pass to the sense
organ and are found twining around the taste cells in the taste buds.
The other branches, the axones, pass into the brain stem and finally end
in some brain center. The question, then, is, Do the taste fibers which
are found in the lingual branch of the fifth nerve have their cell
bodies in the gasserian ganglion, do those found in the ninth nerve have
their cell bodies in the petrosal ganglion and those found in the tenth
nerve have their cell bodies in the jugular ganglion? These are indeed
difficult questions to answer. Reliance must be placed largely upon the
results of surgical operations upon these nerves and ganglia, with their
resulting effects upon the sense of taste. Earlier reports of surgical
operations in which the gasserian ganglion was removed were that the
taste sense on the tongue was completely destroyed, suggesting that all
of the gustatory fibers of the tongue had their origin in the gasserian
ganglion. Later reports, however, were that only the taste sense of the
anterior two-thirds of the tongue was destroyed by this operation,
suggesting that the fibers found in the glossopharyngeal nerve were
independent of the gasserian ganglion and really had their origin in the
petrosal ganglion, these fibers getting into the lingual branch of the
fifth nerve by a circuitous route.

The experiments of Cushing indicate, further, that operations with
removal of the gasserian ganglion produced a dulling or complete loss of
the sense of taste in the anterior two-thirds of the tongue, but this
loss was followed later by complete recovery. The interpretation of
these facts must be that the temporary effect upon the taste sense is
only an incidental result of the operation and that the taste fibers for
this part of the tongue originate in the geniculate ganglion, which is
the ganglion for the facial, or the seventh, cranial nerve, and only get
into the lingual branch of the fifth by way of the chorda tympani nerve.
Consequently, the chorda tympani, a connecting link between the seventh
and the lingual branch of the fifth, is extremely important for the
taste sense, since it carries all of the fibers concerned in the taste
function of the anterior two-thirds of the tongue. This nerve passes
across the cavity of the middle ear, and when stimulated mechanically,
chemically, or electrically at this point is said to arouse taste
sensations variously described as sour or metallic, sometimes as sweet
and bitter. Salt tastes alone have never been reported as resulting from
such stimulation.


[Illustration: Fig. 3.—Diagram showing some of the various courses which
have been advocated for the taste fibers in man. (Courtesy W. B.
Saunders Company.)]


The taste fibers of the vagus seem to have their cells of origin in the
jugular ganglion of that nerve. Thus, while taste fibers are found in
the fifth, ninth, and tenth cranial nerves, it seems that the fibers
really originate in the seventh, ninth, and tenth nerves. The
accompanying figure (Fig. 3.), after Cushing, will show the facts about
the distribution of the gustatory fibers.


                      _The Cerebral Taste Centers_

The first unit in the path connecting sense organ of taste and brain,
represented by the neurones having their cell bodies in the ganglia
described above, all end in the medulla oblongata, in the neighborhood
of the fourth ventricle. These terminals, called the primary sensory
nuclei for the seventh, ninth, and tenth nerves, are all included in the
nucleus of the solitary bundle.

From these primary sensory nuclei a second series of conducting units
begins, sending their fibers in two directions, downward into the spinal
cord and upward toward the higher brain centers. Those fibers passing
downward make connections in the medulla with the motor centers
controlling mastication and swallowing and in the cord with the various
motor centers. These connections make possible the reflex responses to
taste stimuli, such as secretion of gastric and the other juices of the
alimentary canal. Little is known about the course taken by the fibers
which must carry the gustatory impulses from the primary sensory nuclei
to the higher brain centers. It is quite likely that this second
conduction unit is represented by fibers which mingle with those
carrying impulses from the sense organs of skin and muscles to the
higher centers, and which are found in the median fillet, or the pathway
in the brain stem for body sensations. These fibers end in the
thalamus.[7] In the thalamus a third conducting unit begins and carries
the impulses to a still higher center in the cortex of the cerebrum.
Exactly what course the fibers take from the thalamus, or just where the
cortical center for taste is, has not been definitely determined for
human beings.

Footnote 7:

  The thalamus is a center in the upper part of the brain stem, where
  connections are made between the cortex or outer layer of the brain
  proper and lower centers of the nervous system.

Indeed, less is known about the localization of the taste function in
the cortex than about any of the other special senses. This is not due
to lack of interest, for a large number of researches have been reported
in this field. The reason is, rather, that there are certain
difficulties in the way of its solution. First, the help to be got from
physiological experiments upon animals is limited, because of the close
relation between the senses of taste and smell, with the consequent
uncertainty in interpreting behavior after surgical operations. And,
second, since the exploration of the most accessible portions of the
cortex has not revealed a taste center, it is probably located somewhere
upon the ventral, or mesial, surfaces of the cerebrum, where
experimental work is practically impossible. Clinical and physiological
investigations have furnished conflicting results. A survey of recent
work suggests that the most probable center for taste is in the
hippocampal gyre near the anterior portion of the temporal lobe. No more
definite localization is at present possible.


------------------------------------------------------------------------



                              CHAPTER VII

                       TASTE-PRODUCING SUBSTANCES


                   _Adequate and Inadequate Stimuli_


EVER since the doctrine of the specific energy of sensory nerves was
presented by Müller, and since modified into the specific energy of
sense organs or of cerebral centers, two sorts of stimuli for a sense
organ have been spoken of. There are those called _adequate_,—for which
the sense seems to be especially adapted,—and those called _inadequate_,
to which the sensory mechanism is sensitive by virtue of its possession
of a general irritability or sensitivity. It is a matter of common
knowledge that one sees because his visual mechanism is stimulated by
light, or rather by the vibrations of the luminiferous ether, and that
this is the appropriate stimulus for visual sensations. But it is just
as well known that if one receives a blow upon the head he will see
“stars,” or if he presses his finger upon his eyeball he will see
patches of light. The sensations produced in this latter fashion are due
to the mechanical stimulation of the sensitive visual mechanism, which
responds with its specific kind of sensation. The questions to be
answered in this chapter are,—What is the kind of stimulus to which the
taste mechanism is especially adapted? and, Are there other or
inadequate stimuli which can produce taste sensations? In answering
these questions it is well to keep in mind the biological function of
the sense organ of taste. Situated as it is at the entrance of the
alimentary canal it has been called the “eye of the stomach,” whose duty
it is to prevent the entrance into the body, by way of the mouth, of
harmful substances. If this is so, the adequate stimulus for taste would
be any kind of substance which might be taken for food.


                        _Adequate Taste Stimuli_

All substances may be classed either as _sapid_, tastable, or _insipid_,
tasteless. And one of the main conditions for sapidity is solubility. A
substance to be tasted must enter the mouth cavity as a fluid or else
after being taken into it must be dissolved in the saliva. Thus, the
adequate stimulus for the taste organ may be said to be a fluid.
Recalling the structure and location of the sensory ends of the taste
mechanism, it is at once inferred that only fluids can enter the taste
pore and stimulate there the nerve endings of taste. It might then be
assumed that all fluids should produce taste sensations. But all soluble
substances are not sapid or tastable. Consequently, other conditions of
sapidity have been sought, among them being chemical constitution.

One of the most interesting attempts to solve the question of the
conditions of sapidity is that which makes the only condition necessary,
the contact of the substance with the nerve endings within the taste
buds. Now, Graham pointed out that all tastable substances belong to the
class of crystalloids, while tasteless substances belong to the
colloids. It is known, too, that living membranes are permeable by
certain solutions and not by others. Colloid membranes, of which all of
the mucous membranes of the body are examples, are impervious to
colloids in solution, while the passage of crystalloids in solution is
rapid. Hence, no colloids, even those in solution, could actually reach
the free nerve endings of the taste buds. As Nagel says, however, the
truth of this assumption is not easy to settle, since it is very
difficult to get pure colloids and to make sure that their chemical
constitution is not modified by the saliva before contact with the taste
nerves. Other possibilities will be discussed in the chapter dealing
with the theories of the taste function. It will be sufficient here to
say that the adequate stimulus to taste is a liquid, or a solid, or gas,
which may be dissolved in the saliva. Gases such as chloroform vapor,
carbonic acid gas, and the like, were at one time thought to act
directly upon the taste buds, but a safer view is that the gases are
first dissolved in the saliva before acting on the taste mechanism. A
few experiments have been reported in which the gases were said to have
produced taste sensations when the mucous membrane was dry, but it is
practically impossible to produce this condition, since the small glands
of the tongue open directly into the fissures containing the taste buds
and tend to keep the neighborhood of the taste pores in a moist state.

To say that the adequate stimulus for taste is a fluid is to give only
an incomplete description of adequate stimuli. In the case of vision the
adequate stimuli are ether vibrations; and the different visual
sensations, reds, yellows, blues, etc., are attributed to ether
vibrations of different rate.

And in the sense of hearing, the adequate stimulus of which consists of
air vibrations, it is the different vibration rates that account for the
qualitative or pitch differences in sound sensations. What
characteristics of the stimulating fluids are responsible for the
specific sensations sweet, sour, bitter, and salt? The answer to this
question has been sought in the chemical constitution of the sapid
substances. There is found to be a certain relation between chemical
groups and the taste sensations they produce. Kiesow and others have
pointed out that acids are sour; that many chemical salts have a salt
taste; that many carbohydrates taste sweet, and that most of the
alkaloids are bitter. There are too many exceptions to these simple
relations between chemical structure and sensation quality to have them
serve as an answer to our question. There are chemical salts which taste
sweet, there are acids which do not taste sour, and there are chemical
substances whose tastes differ according to their concentration and even
according to the part of the tongue which they affect.

Sternberg, who has made a very extensive study of the relation between
chemical structure and sensation quality, has recognized the
impossibility of finding a simple relation between chemical groups and
sensation quality. His method of study consisted in cataloguing
separately all those substances which taste sweet, sour, bitter, and
salt, and then looking for similarities of structure within the same
sensation group and differences among different groups. This is just the
opposite of the customary procedure which was to take the chemical
groups as a starting point and examine into the tastes aroused by them.
He finds no difference in the molecule of a substance producing a sweet
taste and a molecule of another substance producing a bitter taste, and
finds similarities among the molecules of substances producing different
tastes. He is forced to the conclusion that the tastes are due to the
character of the intramolecular vibrations; that the taste mechanism is
capable of responding to the relations among the atoms which have
escaped the other senses, even when their keenness is increased by all
sorts of artificial devices. Nagel, in reviewing this work of Sternberg,
says that, in spite of the interesting facts which have been accumulated
by him and others, very little has been contributed to the solution of
the question of the stimulus for the different taste qualities.

Before dismissing the question of adequate stimuli one other set of
phenomena ought to be mentioned. There are cases in which sapid
substances dissolved in the blood produce taste sensations. In cases of
diabetes, where sugar is present in the blood, a sweet taste is
experienced in the absence of stimuli upon the tongue surface. Also, in
cases of jaundice, where there is an excess of bile, a bitter sensation
may be experienced. Here the stimuli affect either the taste nerves or
the taste buds directly. There is no reason to think that the
stimulation process differs in any other respect from the normal, except
in the mode of access to the taste buds.


                       _Inadequate Taste Stimuli_

Our second question concerns the possibility of other stimuli to taste,
or of inadequate stimuli. Among these forms of stimulation three will be
considered, namely, mechanical, thermal, and electrical. Are taste
sensations produced by mechanical stimulation of the sense organ? Some
of the older experimenters reported that tapping the tongue lightly or
putting it under slight pressure aroused taste sensations of sour and
bitter. But there does not seem to be good ground for such a conclusion.
No doubt under poorly controlled conditions such mechanical stimuli
might serve to force sapid substances already upon the tongue into the
taste pores and thus stimulate the taste nerves. This, however, would be
only an indirect effect of mechanical stimulation and not at all
analogous to the visual sensations produced by mechanical stimulation of
the eyeball.

It is rather interesting to note in this connection that mechanical
stimulation of the chorda tympani nerve, which carries the impulses from
the anterior two-thirds of the tongue, is said to produce taste
sensations. In cases in which the eardrum has been removed, stimulation
of the nerve in the middle ear is said by some authorities to produce
sweet and bitter sensations, and by others nothing but pricking
sensations.

Thermal stimuli when applied to the tongue do not cause taste
sensations, but only sensations of warmth and cold. Thermal stimuli,
however, are recognized to have considerable influence upon the effect
of taste stimuli. Two cases are to be noted, that in which the sapid
substance itself is either warm or cold and that in which the mouth has
been subjected to warm or cold stimuli before the sapid substance is
introduced into the mouth. The first condition has received the more
attention on account of the importance of temperature in the supposed
chemical reaction in the taste buds and the consequent possibility of
interpreting the facts in favor of a chemical theory of taste. Both
problems have been investigated by Kiesow and others, and the
conclusions are conflicting. Some find that there is a certain optimum
temperature for sapid bodies at which the taste sensations are best
obtained, although there is no perfect agreement as to what this optimum
temperature is. It varies from 55 to 120 degrees F. for different
authors. At the optimum temperature the least quantity of the sapid
substance is necessary to arouse a taste sensation, while a deviation
from this temperature in either direction requires a stronger stimulus
to arouse the same sort of a sensation. Kiesow, on the other hand,
believes that the temperature of the sapid substance makes no
difference, but only the temperature of the mouth previous to receiving
the sapid substance. For instance, he holds that the sensitivity is just
as acute when the temperature of the sapid substance is 32 degrees F. as
when it is 100 degrees F. But if the tongue is placed in water at 32
degrees F. for a few minutes it then becomes insensitive to sapid
substances,—a kind of anesthesia results. He believes that the
conflicting results obtained by the other investigators are merely the
results of distraction of the attention. Whenever the temperature rises
or falls beyond a certain point, then this temperature sensation becomes
more impressive than the weaker taste sensation, and the taste sensation
drops out of consciousness. It is a well-established fact, at any rate,
that thermal stimuli cannot directly arouse taste sensations.

Taste sensations aroused by passing an electric current through the
tongue were reported as early as the middle of the eighteenth century by
Sulzer. Since that time a great number of experimental researches have
accumulated in the attempt to answer the question whether an electric
stimulus can directly arouse taste sensations, as it will produce
sensations of light when it stimulates the eye. In all of this work
there has been rather general agreement as to the character of the taste
sensations present during electrical stimulation. Thus, when the anode
(positive pole) comes into contact with the tongue the taste is said to
be sour, while at the point where the cathode (negative pole) touches
the tongue a bitter taste is reported. There is less general agreement
upon the character of this cathode taste, however, than upon that of the
anode taste, some describing it as burning, some as bitter, sweet, or
alkaline.

The great differences of opinion do not concern the character of the
taste aroused by the electric current so much as the real source of the
stimulation of the taste buds. It was suggested by Humboldt about 1800
that the taste sensations were not caused directly by the electrical
stimulation of the taste buds, but rather by certain sapid substances
which were set free within the mouth by the action of the current on the
saliva. It is known that fluid salts can be broken down by electrolysis
in such a way that at the anode an acid reaction, and at the cathode an
alkaline reaction, can be detected. These facts have lent support to the
assumption that the saliva thus acted upon by the electric current
produces tastable substances. An interesting experiment attributed to
Volta about 1800 seemed for a time to refute the whole electrolysis
theory. He used an alkaline fluid for the anode, into which the tip of
the tongue was dipped. Even in this case the characteristic sour taste
was still experienced. But this experiment, like all of the others which
seem to refute the electrolysis theory of electric stimulation, neglects
the fact that the electrolysis may occur within the taste bud itself,
and hence could not be detected by any test of the tongue surface, nor
could the taste sensations thus produced be prevented by immersing the
tongue in any kind of a solution, since this need not displace the
fluids within the taste bud. The experience of both bitter and sweet
tastes at the cathode, if these experiences are genuine, offers some
difficulty for the electrolysis theory. The most that can be said is
that it is quite likely that electrolysis takes place within the taste
bud, but that, in addition to this, there may possibly be a certain
direct action of the electrical stimulus upon the taste buds or their
nerve endings.

From this review of the different ways in which the taste organ may be
affected it appears that the evidence is not conclusive that mechanical,
thermal, or electrical stimuli may arouse taste sensations. Chemical
stimulation, which is usually included among the inadequate stimuli for
the other senses, is the adequate stimulus for the taste mechanism.


------------------------------------------------------------------------



                              CHAPTER VIII

                    FUNCTION OF THE TASTE MECHANISM


                _Function of Tongue and Salivary Glands_


WHEN sapid substances are taken into the mouth as solids, liquids, or
gases they either become dissolved in the saliva or mixed with it. The
glandular activity, with the resulting secretion of the saliva, as
described in chapter V, may begin at the sight of the objects or may not
begin until the substances have come into contact with the linings of
the mouth cavity or tongue. The breaking down of the solid substances
and their mixture with saliva is facilitated by chewing movements and by
the movements of the tongue. When the substances have been transformed
into the liquid state they move toward the back part of the mouth, from
which the swallowing reflex movements will carry them into the gullet
and stomach. In the course of this movement the fluids will come into
contact with the tip, the superior surface, and sides of the tongue, and
with portions of the mucous linings of the mouth. And it is just in
these regions that we find that the taste organs are located.

The uneven surface of the tongue, due to the presence of the papillæ,
tends to retard the movement of the fluid substances and to give them
time to affect the taste organs. It will be recalled that on the tip and
the superior surface of the front part of the tongue there are few taste
buds found, even where the papillæ of the filiform and fungiform type
are numerous, but a tremendous number of free nerve endings are found
close to the surface of the epithelial covering of the tongue. They can
be affected by the fluids without passing through a gustatory pore into
the taste bud. Now, it happens that the latent time of the sweet sense
is very short compared with that for bitter. And since it is known that
the bitter sensations are aroused especially by stimulating the
circumvallate papillæ, which contain real taste buds, it seems quite
probable that the free nerve endings in the forward part of the tongue
are real sensory ends of taste and are directly affected by the fluid
stimuli. It was at one time supposed that sweet tastes could not be
aroused on this part of the tongue without the aid of tongue movements.
Although this is no longer believed, it is, nevertheless, likely that
tongue movements which would press its surfaces against neighboring
parts of the mouth cavity would bring the sapid substances into contact
with the free nerve endings, and that more quickly than in the absence
of any movement.

As the fluids pass over the sides and superior surface of the tongue
still farther back they meet the foliate and the circumvallate papillæ.
The character of these papillæ is well adapted to retard the fluids in
their passage and give ample time for stimulating the taste nerves. The
former does this by holding the fluid in its long folds, or ditches, and
the latter by collecting it in the circular ditches surrounding the
papillæ proper. In these two types of papillæ real taste buds are found,
with their taste pores leading from the surface into the interior of the
taste bud. It is necessary, then, that the fluid be retained long enough
to reach these hidden parts. As might be expected, there is a rather
long latent time for the sensations aroused in these parts, namely, sour
and bitter.

Tongue movements would be of service here, perhaps even more than in the
forward portion of the tongue, in forcing the fluids more rapidly
through the taste pore. But the tongue movements are said to be of use
in still another way. The bases of the papillæ beneath the epithelial
layer are supplied with a rich network of small veins. Now, tongue
movements increase the flow of blood to the tongue and these veins
become congested with blood. Thus, the veins form a kind of erectile
mechanism through which the papillæ become swollen, and at the same time
the crevices in the epithelial tissue are opened wider, and easier
access to the taste buds results. This hypothesis of the erectility of
the papillæ is not generally accepted.

The devices in connection with the circumvallate and foliate papillæ,
the circular and linear ditches, for retarding the fluid, may account
for certain other characteristics of taste sensations, namely, the
difference in duration of the taste sensations. Since the depressions
and the taste pores become filled with the sapid substances, the taste
sensations ought to last as long as the fluid remains, or until the
taste organs become adapted to them, and thus interfere with the
production of new and different sensations. But a corrective device for
this defect has been assumed by certain investigators in the form of the
numerous secretory glands found in the mucous membrane of this part of
the tongue. These glands are said to pour their secretions through ducts
into these depressions and flush them out, thus removing stimulating
fluids and making way for new ones. This mechanism would prevent the
confusion which would necessarily occur from the mixture of old and new
sapid solutions in the depressions of these papillæ.


                    _The Function of the Taste Buds_

Real difficulties and differences of interpretation come when
explanation of what takes place in the taste bud is attempted. Such
questions as the following arise, none of which has received a perfectly
definite answer. Theories of various sorts are all that can be offered
in this connection:

1. Does the sapid substance affect the taste-bud cells, or only the
nerve fibrils that twine around these cells?

2. If it affects these cells, does it affect the gustatory cells only,
or both these and the supporting cells?

3. Does the sapid substance really enter the taste bud at all, or only
affect the ends of the cells which form the so-called entrance to the
bud?

4. Regardless of what portion of the taste bud is affected by the
stimulus, what is the character of the effect produced? Is it mere
contact or mechanical stimulation, or is it a chemical process which is
set up?

5. Must different types of receiving structures, of whatever form they
may be, be assumed for each type of elementary taste sensation?

The structural relations among the parts of the taste bud were discussed
in the chapter on Sensory Elements. There it was concluded that the
analogy between the sense of taste and that of certain of the other
senses, especially sight and smell, is not so close as it has seemed to
be. It will be recalled that in these sensory mechanisms there are
modified nerve structures, rods and cones in the eye, and the olfactory
cells in the nose, which are affected directly by the stimuli, and in
which a transformation of the stimulus takes place, with the resultant
nerve impulse. This transformation accompanies a chemical change within
these structures, hence vision and smell are called chemical senses. In
the taste mechanism, also considered a chemical sense, it was natural to
see in the gustatory cells of the taste bud structures with functions
similar to that of the rods, cones, and olfactory cells. But the analogy
between these types of structures breaks down because the gustatory
cells do not have the characteristics of nerve tissue, as revealed
especially by the use of differential stains. In fact, as has been said
above, there seems to be no fundamental difference between supporting
and taste cells. Two further facts seem to indicate that the supporting
and gustatory cells take no primary part in the taste function. First,
there is no more intimate connection between these cells and the nerve
fibrils than that of contact, and the contact seems only incidental to
the supporting function. The endings of the nerve fibrils are free from
the cells. And, second, those free nerve endings in the anterior portion
of the tongue seem to arouse taste sensations without the intervention
of any structures resembling the taste buds or their cells. Thus, the
evidence to date leads to the conclusion that the nerve fibrils alone
are the parts affected by the taste stimulus.

If this hypothesis be correct, is it necessary that the sapid substances
should actually enter the taste bud, or only affect its peripheral end?
Many of the nerve fibrils entering the taste bud pass through its whole
length and end quite near the mouth of the gustatory pore. These might
be stimulated without the entrance of the stimulus within the taste bud.
But there are many of these fibrils which do not reach to the peripheral
end of the bud, but stop far short of this point, and then there are
others that reach the entrance of the taste pore but turn back and end
in the characteristic knob-like formation within the taste bud. In order
that these fibrils may be stimulated upon their ends the stimuli would
have to enter the taste bud.

The answer to the fourth question is indeed the most difficult of all.
What is the nature of this stimulation by which a fluid substance shall
start an impulse along the nerve paths to the brain, which shall there
produce sensation? About this last stage of the process nothing is known
either about taste or any of the other senses. But very well-developed
theories exist to account for the transformation of the physical
stimulus into physiological nerve impulse. For instance, in the case of
vision, the stimulus for which consists of ether vibrations, these ether
waves cause chemical changes in certain hypothetical substances within
the rods and cones of the retina. It is this chemical change which
creates the nerve impulse. In the case of hearing, for which the
stimulus consists of air vibrations, these waves, being slightly
modified by the more superficial portions of the auditory mechanism,
finally cause vibrations of the basilar membrane, which, in turn,
produces the impulse in the auditory nerve.

One of the earliest and simplest conceptions of the nature of the
process in the taste organ was a mechanical theory proposed by Boyle,
about 1675. He thought that the particles of various sapid substances
differed in size and shape and that on account of these differences they
produced different effects in their simple contact with the sensory ends
of taste.

According to Graham, who announced his theory in 1889, sapidity of
substances depends on their chemical constitution, colloids being
generally insipid and crystalloids being sapid, hence this has been
known as a chemical theory. This difference of chemical structure,
discussed on page 94, was made to account for the contact, or the lack
of it, between the substances and the sensory ends, but does not account
for the effect produced upon the sensory ends by the substances reaching
them.

Sir William Ramsay prepared an explanation quite analogous to the
theories of color vision and called it a dynamic theory. According to
him, the real stimulus to the taste organs is molecular vibration, the
different taste sensations being due to stimulation by different rates
of molecular movement. Just as in the case of the luminiferous ether or
of the air there is quite a range of molecular vibration rates, from
exceedingly slow to exceedingly rapid. And, just as in the case of
vision and hearing, so is the taste mechanism tuned to respond to only
the middle range of these molecular vibration rates. Substances may then
be insipid, either because their molecular movements are too slow or too
fast to affect the receiving mechanism. In vision we have the analogous
case of the infra-red and the ultra-violet rays not producing visual
sensations, because they are beyond the range of sensitivity of the eye.
Yet the effect of these rays can be recorded by other means. The rate of
molecular movement depends on the weight of the molecule, so that very
heavy or very light molecules would not produce taste sensations.

About the same time Richet and Gley performed a series of experiments
which seemed to show that the molecular weight of the substance was an
important factor in producing taste sensations. They found that the
intensity of the effect produced by different salts was in proportion to
their molecular weight; that if account was taken of the different
molecular weights of the salts used as stimuli the threshold stimulus
would be the same for all of the salts. But if solutions were prepared
according to the absolute weight of the salts these threshold stimuli
appeared to be quite different for the different salts. Later
experiments have shown that the same relation does not hold for
sour-producing substances, certain sours of very small molecular weight
having the sourest taste.

Sternberg, whose work was mentioned in chapter VII, recognized only two
elementary taste sensations, sweet and bitter, and he found no
differences in the molecule of substances producing these two
sensations. He concludes that it is the intramolecular vibrations that
form the real taste stimuli. By transferring the seat of the activity
from molecular vibration to intramolecular vibration the whole matter
becomes more difficult of solution and verification. Still, the
modification of the theory of Ramsay, made necessary by the work of
Sternberg, would leave its essentials, namely, that vibrations of some
sort form the stimulus and that the sense organ of taste is tuned to
receive only a limited range of vibration rates.

Granting that a dynamic theory as outlined above, with possible
modifications to meet new discoveries, is correct, still another
question requires an answer. In the visual organ affected by ether
vibrations of different rates every theory assumes certain parts of the
mechanism sensitized especially to certain vibration rates. To take the
theory of Hering, for example, there are three photochemical substances,
one decomposed by a relatively slow vibration rate, another by a more
rapid vibration rate, and so on. And in the auditory mechanism there is
the _basilar membrane_, capable of vibration in parts in sympathy with
different rates of vibration of the air. The answer to this question
concerning the taste sense is peculiarly difficult, in that it is
impossible to stimulate individual taste buds, and even difficult to
stimulate a single papilla, which may contain many buds. And then it
must be further borne in mind that each bud contains many nerve endings,
so that what is stimulated in experimental work is really a very complex
portion of the sense organ.

As mentioned in another connection, certain papillæ when stimulated with
various substances respond to but one, e.g., sweet, sour, bitter, or
salt, while others respond to two or three stimuli. Further, it is well
known that certain portions of the tongue when stimulated produce a
predominance of certain kinds of taste sensations. On the other hand, an
examination of the taste buds or of the nerve endings within the taste
buds shows no differences among them. Still, in this respect taste does
not differ from sight. The cones of the retina, which are sensory ends
of vision, show no differences in structure, and it is generally
believed that all of the elementary sensations can be produced by the
stimulation of one single cone. If it be true that the nerve fibrils in
the taste buds themselves receive the stimulus, then any specific
characteristics of the receiving mechanism would have to be looked for
in these nerve endings.

Oehrwall has accounted for the facts of the specific sensitivity of
different parts of the tongue and of different individual papillæ
mentioned above by the assumption that each taste bud has a specific
function and that certain papillæ of the tongue have buds all of one
sort, other of two sorts, and so on. Nagel prefers to modify this view
to the extent that each taste bud is capable of arousing every
elementary sensation, but is adapted to respond best and easiest to a
certain specific stimulus with a certain elementary sensation. This view
is analogous to that of the visual photochemical substances which,
according to the Helmholtz theory, were each sensitive to all wave
lengths of light, but not equally.

The previous review of theories does not consider the possibility of the
specific energy of brain centers, rather than of the peripheral sense
mechanism—that is, the possibility that the sensation qualities, sweet,
sour, etc., may be due to structural characteristics of brain centers,
rather than of sense organs. This is a question which is unsolved for
other senses and consequently is not peculiar to taste. The present
tendency seems to be toward attributing the different sensation
qualities to the sensitivity of the sense organ, or else to divide it
between brain center and sense organ. The following facts are considered
as indirect evidence of the specific energy of the sensory ends of
taste: (1) The distribution of taste sensitivity over the tongue. (2)
The effect of certain drugs, e.g., cocaine, which destroys the taste
sensations one at a time. This suggests that the sensory ends that have
to do with the different sensations are differently affected by the
drug. (3) The fact that the same substance as it passes over the surface
of the tongue arouses different sensations, e.g., sodium sulphate, which
is sweet on the tip and bitter on the back of the tongue.


------------------------------------------------------------------------



                               CHAPTER IX

               THE DEVELOPMENT OF TASTE IN THE INDIVIDUAL


                       _Development Before Birth_


THE structures concerned with the taste sensations develop early in the
life of the human embryo. As early as the twelfth day the rapid
development of the head end of the embryo causes an infolding of the
_ectoderm_ (outer layer of the embryo), which later forms the mouth and
nasal cavities. And about the twelfth week the mouth structure is fairly
complete. It has at this stage become separated from the nasal cavity
through the growth of the hard and soft palate.

At the twelfth week the tongue is also fairly well developed as a single
organ, although originating from three or four separate parts which grow
together. The anterior two-thirds of the tongue—that is, all of that
portion back to and including the rows of circumvallate papillæ of the
adult tongue,—grows from the floor of the original mouth structure. It
is in this portion alone that papillæ are to be found. At the end of the
fourth week the circumvallate papillæ begin to appear and at the twelfth
week the fungiform and filiform papillæ begin to appear.

About the fifth month there begins a multiplication of the cells in the
germinative layer of the epithelium covering the tongue, which marks the
beginning of the taste buds. At the eighth month the development has
advanced so far that the gustatory cells can be distinguished from the
supporting cells, and the whole taste bud has separated itself somewhat
from the surrounding tissue. The nerve fibrils found in the fully
developed taste bud come into connection with the gustatory cells very
early in their history—in fact, the presence of the fibrils is
considered by some authorities as the stimulus to modification of the
epithelial cells into those special forms and the consequent formation
of the taste buds.

At birth the most essential parts of the taste mechanism seem to be
fully developed and able to function. The taste buds and the taste pores
by which they communicate with the tongue surface have the same
structure as in the adult. The papillæ, however, according to Stahr,
have not attained the adult form. From an examination of the tongues of
a large number of newborn babies he reports that the foliate and the
circumvallate papillæ are not complete, the depression surrounding the
latter being broken in places and one papilla not clearly distinguished
from others. The fungiform type, too, does not at this stage resemble a
toadstool, as it does in the adult, but they are more like very large
filiform papillæ. Microscopical examination shows both of these types of
papillæ to carry their taste buds on the top, rather than far down upon
their sides. In no case did Stahr find a fungiform papilla without one
or more taste buds.

The distribution of the taste buds over the surface of the mouth cavity
of the fetus and the newborn, as determined by histological examination
and experiment, is very extensive, as compared with the adult. The
presence of taste buds and of taste sensitivity has been reported upon
the arches of the palate, over the whole dorsal surface of the tongue,
and the inside of the cheeks. Buds are especially numerous upon the tip
of the tongue.


            _Development of Taste in Infancy and Childhood_

After birth certain changes occur in the taste organs. During the whole
period of lactation the tip of the tongue remains especially sensitive
to sweet stimuli, a valuable condition for the promotion of the
food-taking reactions in the infant. During this period also the whole
superior surface of the tongue remains sensitive to taste stimuli, but
with increasing age there appears a region of insensitivity just back of
the sensitive tip. At the same time there is said to be an increasing
sensitivity upon the edges of the tongue.

The insensitive zone differs in extent for the different elementary
tastes, but is fairly large for all. These progressive changes in
sensitivity have been explained as the result of the appearance of the
teeth and their importance in the bodily economy. While the individual
lacks teeth and subsists on a milk diet the process of nourishment is
best accomplished by having the food pass directly back over the
superior surface of the tongue until it reaches a point where the
swallowing reflexes are set up. However, after the teeth appear and
mastication of food is necessary, then it is better that the food should
pass from the tip of the tongue to either side, where it will come
between the teeth! Thus, seeking the maximum taste sensation from the
food is equivalent to placing it in a position to be thoroughly
masticated. Further, the presence of food, and especially sour food,
upon the sides of the tongue forms the stimulus to the flow of saliva, a
necessary factor in preparing the food to be swallowed and digested.
Now, if the superior surface of the tongue were highly sensitive to
taste stimuli there would be a tendency to hold the substances upon that
part in order to prolong the pleasure, thus retarding the proper
mastication of the food.

A simpler explanation of the decreasing sensitivity of the upper surface
of the tongue and the increasing sensitivity of the sides is the fact
that, after the teeth appear, chewing would tend to collect the
dissolved food substances at the sides of the tongue, rather than upon
its dorsal surface, hence the greater importance of the taste buds upon
the sides of the tongue.

It is difficult to see why the inside of the cheeks should be sensitive
to taste stimuli in young children and why this sensitivity should be
lost in the adult. Titchener has suggested that its presence in children
may account for their desire to take large mouthfuls of food, thereby
getting maximum taste sensation.

Whatever the biological interpretation of these changes may be, certain
structural changes have been noted which seem to account in part, at
least, for the changed sensitivity. The circumvallate and foliate
papillæ become complete during the first few months and the taste buds,
instead of being located upon the top of the papillæ, are now found
rather low down upon their sides. The change in the fungiform type is
more pronounced. These, more or less conical in shape at first, begin to
acquire an enlarged head (by the growth of secondary papillæ, according
to Stahr). Not only this, but the taste buds in all of them are now
found to have moved from the top to the sides of the papillæ, and many
of the buds have disappeared altogether, some of the papillæ apparently
losing all taste function. There are various opinions as to how the buds
change their position or are lost, but none of these are well enough
established to need description.

Thus, by the completion of growth in the circumvallate and the foliate
papillæ and by the degeneration of the fungiform (loss of taste buds)
the region of greatest sensitivity is transferred from the tip to the
sides and back part of the tongue, while the zone just back of the tip
becomes entirely taste blind.


                          _Taste in the Adult_

The most striking characteristics of taste in the adult as compared with
that of the child, then, is what appears to be a gradual reduction in
the extent of distribution of taste sensitivity and a shifting of the
region of the greatest sensitivity. No doubt there are other changes,
e.g., a general reduction in delicacy of taste analogous to the sort of
change which is noted in the other senses as age advances. In extreme
old age such a condition is quite pronounced. In hearing, for example,
there is not only a dulling sensitivity but a shortening of the range of
audible pitches, especially in the region of the higher pitches. So, on
the tip of the tongue, sensitivity may be very much reduced or disappear
entirely. These changes in taste are not commonly brought to one’s
attention as are those of sight and hearing, because they affect our
life less vitally. But there is little doubt that careful tests would
reveal them.


       _Structural and Functional Differences Among Individuals_

It has been suggested that individuals differ considerably in the
distribution and function of their taste mechanism. In the search for
general laws these variations within the limit of normality have been
looked upon as troublesome exceptions and not of much interest. And
these differences are no doubt responsible for the lack of agreement
among investigators on many points. For instance, there are persons
whose sensitivity on the tip of the tongue is so poor that sweet tastes
can be aroused only with the aid of tongue movements. This and other
similar cases have given cause for the belief in the necessity of tongue
movements for arousing all taste sensations. Some investigators have
found the tonsils and the uvula sensitive, while others have found them
insensitive. When one finds such conflicting statements from men like
Nagel and Kiesow, individual differences seem a plausible explanation.
No special studies have been made of these individual differences.
Consequently, about all that one can say is that the distribution of the
taste buds in different people is subject to considerable variation and
that on this account one cannot definitely mark out the limits of their
distribution which shall hold for all persons. The same is true of the
distribution of sensitivity to specific taste stimuli, sweet, sour,
bitter, and salt substances. Such vague statements as are usually made,
namely, that sweet is best tasted upon the tip of the tongue, sour upon
the sides, bitter upon the back, and salt over nearly the whole tongue,
are true, but when one attempts to assign definite limits to these
regions then great individual differences appear.


          _Individual Differences Due to Pathological Changes_

More extreme variations in taste are frequent as an accompaniment of
disease or congenital malformation of the cerebrum. These variations may
be in the nature of absence of sensitiveness, dull (hypo) sensitivity,
or very high (hyper) sensitivity. Only one case, so far as we have
found, has been reported of congenital taste blindness, either for all
taste sensations or for one or two of them, such as would correspond to
hereditary color blindness of the various sorts. The apparent absence of
taste in certain idiots is not a form of taste blindness to be compared
with color blindness. Such persons will eat sulphate of quinine with as
much enjoyment as sweet food, but so will they try to eat wood or stones
or paper. Nor are the cases, which are more or less common, of dulled
taste sensitiveness as a result of cerebral malformation to be compared
with real color blindness, which, as far as is known, at least, depends
upon no such cerebral abnormality.

There are cases of acquired taste blindness, either general or for
special qualities, which resemble in general character acquired color
blindness. In both senses the blindness results from pathological
changes in the sensory mechanism, either in the sense organ, its centers
within the brain, or its connecting nerve trunks. The nature of the
sensory defect depends upon the extent of the pathological change and
its location. Thus, there may be general taste blindness if both of the
cerebral centers are involved, a defect on only one side of the tongue
if one cerebral hemisphere is involved. And if the disturbance is in the
nerve trunks, only the anterior two-thirds of the tongue may be
affected, or only its posterior third. Again, if the lesion is in the
sense organ itself, one or more specific taste qualities only may be
lost, or all qualities for a very small portion of the tongue. These
latter cases are of much importance in developing an adequate theory of
taste function. Nagel describes a case in which all sorts of taste
stimuli produced only a sensation of salt on one side of the tongue,
while on the other side taste was normal. This peculiar condition was
followed by a total loss of sensitivity on the affected side.

Epileptics are said to show taste abnormalities of varying character
after an attack, and lasting for hours in some cases. There is usually a
loss or dulling of the sense, most prominent for salt and least
noticeable for bitter. Such conditions are not peculiar to the taste
sense, for there is usually a disturbance of the other special senses
also after an epileptic attack.

All sorts of taste abnormalities are found in hysteria, but little is
known of their underlying causes in the taste mechanism. There may be
either hyper- or hypo-sensitivity, although the latter is more common;
and both sides of the tongue or only one side may be affected, or even
only a small portion of the tongue may be involved. Here, too, the taste
abnormalities are accompanied by disturbances of the other senses.

Criminals, especially those recognized as degenerate, show taste
abnormalities, usually extreme dullness of taste, along with the same
sort of defect in the other senses. Attempts have been made to find a
positive correlation between keenness of taste and number of stigmata of
degeneration, but with no success.

Any condition affecting the mucous lining of the mouth cavity may be
expected to modify taste sensitivity. For instance, burning the tongue
with a hot drink will destroy taste for a time. Tumors and abnormal
thickening of the epithelium of the tongue will likewise disturb the
taste function. These effects are clearly due to a direct action upon
the taste buds or the gustatory pores, and may be local or general in
character. Under this head might be mentioned the effects of drugs
applied to the tongue surface, but they have been discussed elsewhere.
Hallucinations of taste likewise, of which there are a great variety,
have been described in another connection.


 _Racial Differences in the Structure and Function of the Taste Organs_

A number of races, e.g., Negroes, Japanese, Europeans, etc., have been
studied to determine differences in the taste mechanism, but little of
significance has been found. The number of papillæ upon the tongue is
just about the same in every case. The slight differences of size and
arrangement of the papillæ, especially the circumvallate type, are not
such as to be of much importance from the functional point of view. The
variation in these respects is so large within any one racial group that
there is little likelihood of finding significant racial differences.


------------------------------------------------------------------------



                               CHAPTER X

                           EVOLUTION OF TASTE


               _Sensitivity of the Unicellular Organisms_


THE study of the sense organ of taste in adult human beings consists of
an examination of the taste sensations resulting from controlled
stimulation of limited parts, supported by the microscopical examination
of the structures found in the regions in which these taste sensations
can be aroused. The relation of cause and effect is then assumed.
Neither method taken alone will suffice, as there always remains the
possibility of function in the absence of definitely recognized taste
structures and also the possibility of the presence of functionless
structures. The difficulties and uncertainties arising in this combined
study of structure and function have been discussed in earlier chapters.

But if the determination of the taste organs and their localization
offers difficulties in the adult human being, these are multiplied many
times when the study is carried to the lower animals. The method of
stimulation is greatly limited, to what extent depending upon the kind
of animal studied, because the results of the application of stimuli
must be interpreted from the forms of behavior exceedingly crude,
compared with the language behavior of man. This handicap in the study
of taste is great, as compared with sight and hearing, at least, on
account of the extremely close relation between the taste and smell
organs in position and in the nature of their appropriate stimuli. In
case of certain of the lower animals the assumption of distinct states
of consciousness corresponding to our experiences of taste and smell is
unwarranted, as is even the assumption of any consciousness at all.

The study of taste structures reduces itself largely to the search for
sense organs resembling those of man, and in the same neighborhood as
they are found in man. Here again the difficulty is especially great in
taste, because the taste organs even in man are not very highly
differentiated from other structures, and the really essential part of
the organ is not definitely known. (See Chapter VI.) In the search for
taste in lower animals one must rely much upon the expectation of
finding the taste mechanism in the mouth or its immediate neighborhood.
Structures found here and not known to function otherwise are likely to
be looked upon as taste organs. These assumptions from location are then
tested by stimulation of the parts with sapid substances and looking for
characteristic responses, and further by extirpating these organs and
noting the effect upon behavior. Other criteria of sensitivity, which
can be used especially in the study of sight and hearing, such as rate
of fatigue, reaction time to stimulation, and the like, are of little
use on account of the above-mentioned close relation between taste and
smell.

When looked at from the evolutionary point of view, all of the senses
are seen to have developed through modification of the _sensitivity_ of
a single structure, the cell, with its additional properties of
conductivity and motility. In the simplest living organisms, for
instance, one finds sensitivity to consist in the irritability common to
all living cells, and the sense organ to be represented by the whole
cell. Still, the amœba, one of these unicellular organisms, reacts
differently to the contact of food substances and to purely mechanical
stimulation. And the white corpuscles of the blood in the human body are
said to adjust their behavior according to the chemical composition of
their surroundings. So, even in this earliest stage of evolution, before
any differentiation of structure appears, one sees a reaction analogous
to the taste reactions of the higher animals.


                         “_The Chemical Sense_”

In the simpler multicellular organisms, which develop by cell division
and multiplication from a single cell, the cells differ from the
original type and from each other in position, structure, and function.
In the course of growth the organism originally spherical in shape
becomes modified by irregular growth of cells, producing folds and
prominences. Cells are crowded out of shape; some lie at the base of a
depression protected from stimulation; others occupy positions which
make them especially liable to be acted upon by such stimuli. In the
course of these modifications some of the cells become especially
adapted for receiving impressions, others for conducting or transmitting
these impressions to various parts of the organism, others for producing
movements of the organism. It is with the first type of cell that we are
concerned, the receptor mechanisms. They are in the simpler organisms,
adapted to receive two sorts of stimulation, mechanical and chemical. In
fact, through the whole series of multicellular organisms such reactions
to mechanical and chemical stimuli have been noted more or less
definitely, although special sense organ structures have in many cases
not been discovered. This is especially true for the reactions to
chemical substances. It is customary to speak of the “chemical sense,”
to signify these responses to chemical substances, without any attempt
to differentiate between smell and taste. Obviously, in the case of
organisms which live in a fluid environment, this chemical sense might
be called taste, since it would correspond in a way to that sense in
man, for which the adequate stimulus is a fluid. But since it is a
“distance receptor,” in that objects at a distance can produce
responses, probably by diffusion of substances in the fluid, it might
also be looked upon as more nearly resembling the smell sense. In most
cases structure offers no help in settling the matter.

In the medusa, or jellyfish, one of the earliest forms in which a
nervous system and sense organs are found, the tentacles are especially
sensitive to chemical stimuli, much less so to mechanical stimuli. To
the former they respond by shortening and twisting themselves about the
object. As for sense organs in these parts, there are small club-shaped
papillæ in the neighborhood of the tentacles, differing somewhat in
character in the different species. These papillæ contain a narrow canal
lined with thick cylindrical cells. As far as both structure and
function are concerned, they may be considered either as taste or smell
organs.

In the flat worms, where a nervous system with a rudimentary brain is
found, the reaction to chemical stimulation is not clear. This organism
has specialized responses, among which is a movement toward food placed
near it. But whether this is a reaction to chemical stimuli alone or
combined with mechanical is not known. No taste organs have been found.
Pits or depressions found on the lateral surface of the anterior end of
the worm, and supplied with nerves from the brain, have been regarded as
olfactory rather than as taste organs.

In the annelid group, of which the earthworm may be taken as an example,
there are well-defined chemical reactions, which more nearly resemble
taste reactions than the cases previously mentioned. Here a positive
reaction to food substances seems to occur only when these substances
come into contact with the body. For instance, the characteristic
burrowing reactions of the earthworm are not aroused by placing filter
paper soaked in manure near them, but only when the paper is actually in
contact with the body. Negative reactions, however, to strong chemical
stimulation may take place without contact. Attempts have been made by
Parker and Metcalf to show specialized taste reactions to different
chemical substances by measuring the latent time in the responses to
various substances brought into contact with the body. From such
evidence as this it would appear that earthworms have specialized
reactions to the chlorides of sodium, potassium, lithium, and ammonium,
which are indistinguishable to the human taste sense, with their common
salt taste. These results are interpreted as indicating qualitatively
different effects of the stimuli. In these organisms it has been
possible to discover taste organs, distinct from the olfactory organs.
They are described as cup-shaped organs, which may be either depressions
or prominences. They occur in large numbers and are widely scattered
over the body. They are said, however, to be especially numerous at the
edges of the mouth and within the mouth cavity.

The crustacea, among which are the crabs and the lobsters, characterized
by their hard shell-like covering, show certain specific reactions to
chemical substances when these come into contact with the parts of the
body near the mouth. Reactions to chemical stimuli applied to any part
of the body of the crayfish have been reported by Bell. The positive
reactions were such as to bring the substance toward the mouth and the
negative reactions such as to remove the substance. Responses to such
substances at a distance are uncertain. But it is difficult to
differentiate between possible smell and taste reactions. The sense
organs in these organisms are usually located upon the antennæ, or
feelers, in the neighborhood of the mouth. Here there is a different
kind of response to chemical and mechanical stimulation. No structures
with a specific taste function have been described, although smell and
tactile organs have been localized.

In the organisms described above, the chemical, or, more specifically,
the taste, sense is a food sense,—edible and inedible substances causing
reactions of different character. The reactions to stimuli within the
edible group, however, show no variation. In the insects, especially the
ants, bees, wasps, etc., there seem to be qualitative differences in the
effect produced by chemical substances. It is by means of this chemical
sense that bees and ants are able to find food at a distance, to return
to their homes under all sorts of adverse conditions, and to distinguish
nest mates from enemy intruders. But, since these are all reactions to
stimuli at a distance, they must be attributed to the smell sense,
rather than to the taste sense. But in the case of these organisms a
sharp distinction between smell and taste seems possible. Forel and
others have offered honey mixed with strychnine to ants, who seized it
greedily, indicating an olfactory sensibility. But immediately after the
honey had touched the mouth parts, avoiding reactions, such as to remove
the substance, followed, indicating sensitiveness to the bitter
substance. Wasps and bees will make the same sort of responses if
distasteful substances which are inodorous are mixed with pleasant,
odorous substances. The sensitivity to tastes varies considerably in
different insects, being very great in bees and ants. From such
experiments as the above it has been concluded that the smell organs are
located on the antennæ and that the taste organs are located on the lips
and in the mouth. Microscopical examination shows that in all insects
the tongue and inside of the mouth are covered with minute pits, or
depressions. In each pit there is a minute hair, or rod. Some observers
say that this rod is hollow and perforated at the end, thus
communicating with the nerve which ends at its base. Other observers say
that there is no perforation upon the end of the hair. However this may
be, there seems to be no doubt that these are the taste organs. The same
type of structure has been reported on the proboscis of the bumblebee,
the hive bee, and the common fly. They are said to resemble a hollow
hair, the channel communicating with a nerve fiber at its base. In the
insects, then, we find the earliest definitely specialized taste
mechanism.


                       _Chemical Sense in Fishes_

In the fishes, again, the distinction between the senses of smell and
taste becomes more difficult, on account of their fluid environment.
But, disregarding the distinction between smell and taste, the general
chemical sense plays a very important part in the life of the fish. Now,
some observers have included all of this sensitivity to chemical
substances within the sense of smell, while others have attributed a
part of it to a taste mechanism. As representative of the latter,
Herrick’s conclusions are of interest: “In fishes the gustatory system
is much more extensively developed than in mammals, especially the vagal
part which supplies the taste buds in the gill region. In some species
of fishes, moreover, taste buds appear in great numbers on the outer
skin, and these are in all cases innervated from the seventh cranial
nerve. In the common horned-pouts, or catfishes, and in the carps and
suckers these cutaneous taste buds are distributed over practically the
entire body surface, and especially on the barblets.... These sense
organs and their nerves are entirely independent of those of the lateral
line system, and of the ordinary tactual system, though the gustatory
and tactual systems have been shown experimentally to coöperate in the
selection of food.”

Herrick determined by experiment that the sense organs thus generally
distributed over the body of the catfish really had a taste function.
Food placed at a distance from the fish produces only restless
movements, indicating that the eyes do not direct them to it. But if
food comes into contact with the mouth parts, or, in fact, any part of
the body, it is immediately seized. To show that this reaction is not
alone due to tactual stimulation, the tactual organs were first
stimulated with cotton wool, which produced the characteristic seizing
reaction. But after stimulation was continued for a while reaction no
longer followed. If at this point the cotton wool be soaked with meat
juice, the seizing reaction is again set up. Adaptation to tactual
stimulation has taken place, leaving the taste organs to function alone.
To show further that the responses did not depend on olfactory
stimulation, the olfactory nerves of certain fishes were cut. When the
experiment was performed, after recovery from the operation the
responses were the same as in normal fish.

The experiments of Parker show further that the mouth and external
surface of the body of certain fishes are sensitive to sour, salt, and
alkaline solutions. Sheldon obtained about the same results. The
external skin covering is not sensitive to sugars. The tongue of fishes
presents a smooth, gray, dorsal surface, devoid of elevations or
papillæ, which characterize the tongues of many other organisms. Nor is
it a mobile organ in comparison with other species. On the whole, the
tongue itself seems little adapted for arousing taste sensations.

The system of “lateral line” organs of fishes have at times been thought
to be concerned with the chemical sense. This is probably not the case,
although their exact function is a question still under dispute.

In a general way, the taste buds, or sense organs of taste of fishes,
resemble those of the human being. They are either flask- or cup-shaped,
and are composed of two types of cells, called supporting cells and
taste cells. The latter cells end peripherally in a hair or bristle,
just as the same kind of cell in the human taste bud.


                        _Land-Dwelling Animals_

There seems to be no experimental evidence for a specific sense of taste
in amphibia, or reptiles. But sense organ structures have been described
upon the tongue and soft palate of the frog, where they are said to
occur in hundreds. They are disc-shaped structures, made up of several
kinds of cells, which correspond to the real taste cells and supporting
cells of the human sense organ. The taste cells end peripherally in
several hairs or bristles, and at their central end make connection with
nerve fibers. In the reptile group there is neither experimental
evidence of taste sensitivity nor anatomical evidence of the presence of
taste corpuscles on the tongue or in the mouth cavity.

The experimental evidence for the taste sense in birds is slight. It
certainly is greatly overshadowed by the keen senses of sight and
hearing. Birds seem to represent one case, however, in which taste is
more important than smell. Taste sensitivity for different chemical
substances, in the case of young chickens, at least, seems clear from
certain studies of instinct and learning, in which they accept certain
kinds of food and reject others after tasting them. In considering the
sense of taste in birds it must be remembered that most of them swallow
their food without chewing it or without having it reduced to liquid
form through mixture with saliva. The tongue, which varies in character
considerably in different types of birds, is in most cases covered with
a horny coat. Numerous hard papillæ are found upon its surface.
Microscopical examination of these papillæ shows nothing which can
correspond to taste buds or to gustatory cells. The parrot is said to
form an exception to most birds, in that it has a relatively soft and
fleshy tongue, with numerous papillæ, and also in that it chews its
food.

In the duck, which has a large tongue, there are certain portions which
lack the hard covering common to birds’ tongues. Here, in addition to a
large number of tactile corpuscles, there are groups of cells which
resemble somewhat true taste corpuscles. The peripheral ends of their
cells reach the surface of the mucous covering of the tongue. The cells
do not end in the bristle, or hair-like, formation, as those of the
human taste cells, but in a pointed elongation of the protoplasm.
Experimental evidence of the function of these structures is lacking.

Taste sensitivity and the structure of the taste organs differ greatly
in the mammals, but there seem to be two characteristics in common,
namely, the localization of the taste corpuscles within the mouth and
the importance of the tongue in arousing taste sensations. The character
of the mucous lining of the mouth also shows great variation in the
number of papillæ and the taste buds which they contain. The number of
papillæ varies from two or three in the marsupials and four in the
elephant to an extremely large number in rodents, e.g., the rat. The
papillæ are in general quite similar to the three most common forms in
the human taste organs, the circumvallate, the fungiform, and the
filiform, and have about the same location in relation to each other.
The greatest difference is in the prominence of the fourth type, the
foliate papillæ in certain mammals, as compared with man. These are seen
best in the rabbit, as folds directed downward and forward on the sides
of the tongue in its posterior portion. They have been considered to
result from the great number of papillæ which throw the mucus into
folds. Each foliate papilla is composed of a number of parallel ridges,
each ridge in turn being composed of papillæ of the fungiform type.
Between the ridges there are narrow ditches. It is in the side walls of
these that the taste corpuscles are found in greatest numbers. Thus,
these ditches are analogous, in function at least, to those of the
circumvallate papillæ. Their origin, however, seems to be different from
that of the circumvallate. In the monkey one finds less prominent folds
on the sides of the tongue, rich in taste corpuscles, which represent
the foliate papillæ.

The taste corpuscles themselves have about the same characteristics in
all mammals as in man. There are differences in size, to be sure, but
their structure is the same, and the supporting cells, gustatory cells,
and nerve fibers are present in them all.

This survey of taste in the animal kingdom suggests the conclusion that
the taste organs represent a modification of the original skin
sensitivity or touch sense, and surely a slight modification when
compared with the senses of sight and hearing. A certain resemblance has
been remarked by Wundt and others between the touch corpuscles and the
gustatory corpuscles. His interpretation is that the whole body was
originally endowed with the touch sense, while certain parts being
affected continually by specific sorts of stimuli, became adapted to
them by undergoing modifications of structure. The head or mouth end of
the animal was more subject to chemical stimulation, and the adaptation
of the tactile organs to this particular form of stimulation resulted in
the development of the senses of taste and smell. To consider taste as
one of the lower senses, in the sense of being least highly developed
and the earliest to appear, is justified from this survey of the
evolution of the taste sense, if from no other point of view.


------------------------------------------------------------------------



                               CHAPTER XI

                    GUSTATORY IMAGINATION AND MEMORY


              _The Nature and Frequency of Mental Images_

IT is a familiar fact that in one way or another and in different
degrees to different individuals it is possible to have sensory
experiences without the actual presence of their accustomed stimuli.
Thus, many people can recall “in their mind’s eye” the colors of
objects, their shape and structure, when they are no longer in the
presence of the object thought of. Or, “in their mind’s ear,” they can
hear the blare of a trumpet, the voice of a friend, the hissing of
steam, when no corresponding stimulus is present to the ear. Similarly,
“in imagination” many can experience the tactual feel of velvet, the
odor of onions, the warmth of sunshine, the ache of a tooth, the nausea
of seasickness.

“Thus, I can call up in my mind’s eye, more or less vividly, my boyhood
home, and seem to see, though more obscurely than if I were present on
the spot, the house and barn, the grape arbor, the garden, even my
little bookcase in the library. I can smell the honey in the bee boxes,
and can hear the general hum and stir of the hive. I can do this because
I can call up images of these past experiences. Or, by putting together
the images of wheels, sails, birds, and ropes which I have actually seen
I can create in my mind’s eye an aeroplane of a pattern which has never
yet been constructed.” This constructive performance would constitute
“imagination” as distinguished from mere “imagery.”

These images of imagination are not to be confused with the after
sensations which we have already described. They may be experienced
days, or even years, after the first application of the original
stimulus. Nevertheless, these “mental images,” or “centrally excited
sensations,” are described as essentially sensory in character—they have
the attributes of all sensory experiences, such as intensity, extensity,
duration, clearness, locality, quality, and modality. In fact observers
have been found for whom these mental images were so realistically
sensory that actual negative after sensations, in the case of visual
images, have been reported as following upon them.

In the case of many individuals, these experiences of objects in their
absence are relatively rare and obscure, and in some cases, indeed, are
so obscure as to lead the individual to deny the existence of such
experiences. In still other cases the centrally excited sensations, the
mental images, are experienced in their vivid and, apparently,
immediately sensory form only under special conditions, as in dreams,
hallucinations, drowsiness, or fatigue, or under the influence of
special drugs. It has appeared from the study of mental images that, in
so far as they are present, they are not equally reported in the
different modes of sensation. Visual images in some cases, auditory
images in other cases, and motor images in still others, have seemed to
be so specially frequent, vivid, or easily aroused that at one time it
was customary to classify individuals on the basis of their images as
visuelles, audiles, motiles, and efforts have even been made to adapt a
method of teaching to the presumed “imagery type” of the student. In the
present connection our interest is only in inquiring whether and in what
degree “images of taste” are present.


                        _Mental Images of Taste_

Is there a “gustatory” or taste imagination as well as a visual or an
auditory imagination? It should, of course, be borne in mind that tastes
may be “thought of,” “referred to,” or “indicated” without there
actually being taste qualities present in experience. Thus, I may refer
to the “saltiness of the pork” and discuss it in detail without having
in consciousness the sensory tang and quality of “salt.” The saltiness
may be “represented” in my thinking in this case, not by a taste quality
at all, but by the word which stands for such a quality, or even by a
visual picture of a white granular substance, or an elongated strip of
meat. Only if the immediate and unanalyzable experience of sensory
“salt” is present is there evidence, in this case, of an “image of
taste.”

Obviously, we must mainly rely in such cases on the testimony of the
observer, although there have been investigations made of a more
objective sort, in which it is shown that the reported “images” are so
similar in character to actual sense experiences that the observer,
under appropriate conditions, cannot distinguish between the two.

If we turn to the results of introspection or individual testimony, we
find that if taste images exist at all they are at least reported as
very much less frequent and vivid than are images from other senses.
Thus, one observer, who in the course of two years’ observation of his
own experience recorded 2,500 “images,” classified these as follows:


                           Vision         57%
                           Hearing        20%
                           Smell           6%
                           Taste           6%
                           Touch           4%
                           Movement        3%
                           Temperature     2%
                           Organic         1%
                           Emotional       1%


Much the same state of affairs is revealed if one attempts, when certain
objects are named, to record the imagery which the name evokes. In
response to the word “tornado” some individuals at once report visual
appearances of falling houses and waving trees, while others report
auditory experiences of crashing buildings and rushing wind. Within a
few moments most observers report the appearance of images from various
senses, though some of them are more vivid, more prompt, or more
enduring than others. In the case of taste, however, it is rare that
images are reported as either vivid, prompt, or lasting. Usually when
such an image is reported at all it is described as lagging behind the
images of other modes, appearing to be dragged in or reënforced by them,
and to be transient, weak, and fluctuating. It seems, also, that,
although images of taste are not easily aroused directly by words, their
appearance is facilitated if a visual image or impression is present
with them. Consequently, when the poet or the advertising writer desires
to provoke imagined tastes in his readers he often attempts to arouse
them more effectively by presenting suggestive pictures of scenes
associated with the object, or a tempting array of the articles
themselves in an agreeable setting.


                _Taste in Dreams and in Hallucinations_

Reports of the sensory components of dream experiences show taste to be
an inconspicuous factor in dream life. The following table shows the
results obtained by two independent investigators when dreams of various
individuals were analyzed into the sensory elements reported:

                                   Percentage of
                                    Occurrences

                    Sensory       381        300
                    Mode         Dreams     Dreams

                    Vision       84.5%       67%

                    Hearing      67.7%       26%

                    Touch        10.8%        8%

                    Smell         6.9%        1%

                    Taste         6.3%        1%

Records of the hallucinations of sane and insane people also show taste
to play a relatively minor rôle, so far, at least, as frequency of
report is concerned. In both cases visual, auditory, tactile, and
olfactory hallucinations seem to be more common experiences. “Subjective
tastes,” or tastes which do not appear to be caused by the action of any
substance in the mouth, are, however, by no means unknown, although in
most cases it is apparent that these tastes come from some unsuspected
irritation of the taste organs by actual agents. Substances circulating
in the blood may often be seen to be responsible for these “subjective
tastes.” Thus, in diabetes the excess of sugar in the blood may give
rise to a persistent sweet taste, and in case of jaundice biliary
products often produce sensations of bitter. Various drugs, when present
in the blood stream, also provoke well-known effects in taste, and it is
quite probable that the taste hallucinations associated with nervous and
mental disorder have their origin in some abnormal irritation of the
nerves or brain centers involved in taste. Distilled water, which is
presumably as tasteless a substance as could be found, is reported as
tasteless by only about 50 per cent of observers. About 25 per cent
report it as having a bitter taste, while certain cases are found in
which it tastes sweet, or salt, or sour, or as having some unknown
taste. As the result of careful study of these facts, Brown suggests
that “we may perhaps infer that the ‘taste’ of water is not, after all,
a taste quality, but is due rather to the presence or absence of some
tactual characteristic; the absence, perhaps, of the ‘bite’ which is
associated with sweet, salt, and sour alike.” It is also possible that
mechanical stimulation of the taste organs can produce true taste
qualities, just as mechanical stimulation of the retina produces spots
of light and the tapping of a “warm spot” may produce a faint sensation
of warmth.


------------------------------------------------------------------------



                              CHAPTER XII

                 UNUSUAL AND ABNORMAL TASTE EXPERIENCES


                  _Gustatory Hallucinations and Auræ_


DISORDERS of taste are for the most part neither as varied nor as
bizarre as the abnormal conditions of the more complex senses. Illusions
of taste, hallucinations, and subjective tastes we have already referred
to as frequently found. But of them little can be said, except that they
occur, and that they present very little of psychological interest. The
appearance of these subjective tastes may in some cases be due merely to
the fact that “a taste sensation easily associates itself with certain
muscular sensations. Thus, pressure on the base of the tongue provokes
the movements of vomiting. With this muscular sensation may be
associated a sensation of bitter, which accompanies violent nausea.” In
ways similar to this some observers would explain the reports of others
who find taste sensations to be produced by mechanical stimulation of
papillæ. Most observers do not get such results, and it may be that
these sensations when they are reported are of the associated variety.

In the case of certain abnormal nervous conditions, however, these
features may assume rather striking proportions. Thus, in the “auræ,” or
preliminary symptoms preceding an epileptic attack, the patient often
experiences unpleasant bitter or metallic tastes, and distressing
feelings of numbness of tongue, etc. These sensory manifestations are,
however, by no means as elaborate as are the “auræ” of some of the other
senses, notably hearing and vision.


                     _Partial and Complete Ageusia_

Conditions of partial or complete _ageusia_, or loss of taste, are well
known. Such conditions may result from the local application of various
drugs to the end organs, the paralyzing effect of drugs on the nerve
trunks, injury to, or operations on, these nerves, or damage through
injury, disintegration, or removal of special brain areas.


                  _Taste Hallucinations of the Insane_

In the case of the mentally deranged taste hallucinations are usually
disagreeable, and they are often rationalized into a fabric of
delusions,—foul gases are said to be blown upon them, poisons are being
placed in their food. Such patients behave in realistic manner, making
various defensive reactions, such as stuffing the nostrils with paper or
cloth, spitting, and refusing food. In some cases these hallucinations
of the insane obviously originate from local inflammation in the
peripheral tissues, or from glandular disturbances, and, hence, do not
in themselves constitute important pathological symptoms. In some cases,
however, such hallucinations arise quite independently of such acute
local conditions of irritation, as in chronic psychic disorders or
dementias. Under such circumstances they have greater significance, as
they point to more deep-seated mental and nervous disturbance. Just as
in normal life taste and smell are very closely associated with each
other, so, in these cases of insane hallucinations, disorders of taste
sensation are likely to involve olfactory irregularities as well.


                        _Synæsthesias of Taste_

An interesting though apparently somewhat rare phenomenon in the field
of sensation is what is known as “synæsthesia.” By this is meant cases
in which a given sense quality arouses, or is intimately associated
with, qualities belonging to other sensory modes. Thus, in the case of
vision and hearing, some individuals perceive the different vowel
sounds, or the sound of musical instruments, as having color. One such
person reports that to him all the consonant sounds seem to be very dark
purple, while among the vowel sounds “a” seems yellow, “e” is pale
emerald, and “u” is light dove color.

Taste, far from being an exception in this case, is one of the senses in
connection with which “synæsthesias” must often occur. Salt, for
instance, is described by one observer as dull red, bitter as brownish,
sweet as clear bright red, and sour as green or greenish-blue. To
another observer the taste of meats seems red or brown, the taste of
Graham bread is rich red in color, while all ice creams (except
chocolate and coffee) taste blue. To still another reporter the sound of
the word “intelligence” tastes like fresh sliced tomatoes, while the
sound of the word “interest” tastes like stewed tomatoes. There has been
much speculation as to the probable meaning and mechanism of these
synæsthetic experiences. Investigation seems to show that the particular
combinations are by no means universal, even among those who report such
observations,—they seem to be individual and personal in their nature
and presumably in their origin.

It seems quite probable that in the main these synæsthesias represent
uncritical confusion of sensory qualities with other sensory qualities,
or with the affective qualities, the feelings, which accompany them.
Thus, we often hear such phrases as “bright taste,” “heavy taste,” “dark
brown taste,” “green taste,” “soft taste,” “hard taste,” “smooth taste,”
etc. It is clear in most of these cases that either a touch component is
included in the total taste experience (as in “smooth taste,” “soft
taste,” “hard taste”), or that kinæsthetic (muscular) factors are so
included (as in “heavy taste”), or that the phrase is more or less
designedly an analogy, or other figure of speech (as in “sharp taste,”
“bright taste,” “clear taste”). The basis of such analogies is sometimes
rather easily discerned, and often is seen to be the “feeling tone”
which the sensation arouses,—the effect or “affect” which it produces.
Thus, a heavy weight retards, inhibits, and overpowers us. Some tastes
have this same overpowering affective tone, and may be intelligibly
described as “heavy.” A clear, bright day gives us recognizable feelings
of pleasantness, relief, and gives to objects a distinctness of contour.
Some tastes, being well defined, definitely localized, and highly
agreeable and soothing, may, then, be intelligibly described as being
“clear,” “bright,” or “pointed.” These illustrations represent, to be
sure, only simple forms of such synæsthesias. But even the resemblance
of the sound of “intelligence” to the taste of fresh sliced tomatoes is
by no means incomprehensible when we reflect that “freshness” means
“alertness,” “sliced” suggests sharpness of edge, while tomatoes thus
prepared are usually mature and ripe. For are not alertness, keenness,
and maturity the very marks of intelligence, just as “dullness” and
“greenness,” also sense qualities, are expressive of its absence? In
somewhat the same way we commonly speak of “sweet odors,” “sweet sounds
of music,” or even sweet visual experiences, as in “a sweet face.”

A few individual cases of taste synæsthesia have been studied in some
detail. Such individuals are often shown to have a defective sense of
taste and to rely largely, in their recognition of taste, on touch
accompaniments, affective characteristics, and such “color” experiences
as the various tastes are said to induce.


                         _Perversions of Taste_

Under certain unusual organic conditions, and also still more commonly
in the case of degenerate and neurotic individuals, various perversions
of taste occur. These perversions do not seem to be exclusively
gustatory in character, since they involve more general factors, such as
appetite, craving, and emotional disturbance. The name _parorexia_ is
sometimes given to these perversions of taste and appetite. One of the
subforms, known as _malacia_, takes the form of an urgent desire for hot
spices, or for sour and acid foods, such as pickles. What is known as
“salt hunger” is a very similar condition, especially often found among
the lower animals. Another form of such perversion, known as _pica_,
shows itself in the desire to eat such substances as clay, chalk, and
similar gritty or earthy substances. Especially often among children and
among certain primitive peoples the chewing of these substances often
seems to give a satisfaction quite unfamiliar to the majority of
mankind. Little is known about such perversions beyond the fact that
they have often been reported.

Under certain conditions of mental degeneracy and nervous disorder
perversions sometimes arise which have been classed under the term
_allotriophagia_. This perversion takes the form of eating with apparent
relish various kinds of filth which are commonly offensive and
disgusting. In these cases it is quite possible that there is no genuine
taste disorder. Many, if, indeed, not most, of our revulsions against
substances known as filth arise on the basis of associated
circumstances, rather than on the simple basis of their taste qualities.
The falling away, or deterioration, of these associative and æsthetic
controls in the case of the demented and degenerate, and their absence
in the case of the feeble-minded and imbecile, may easily lead to
reactions which suggest but do not necessarily involve genuine taste
disorder.


------------------------------------------------------------------------



                              CHAPTER XIII

                            FOOD AND FLAVOR


                     _The Biological Rôle of Taste_


IN considering the function of the sense of taste it is common to
dismiss the topic in a summary manner by pointing out the fact, that in
its original primitive conditions, at least, this sense enables the
organism to discriminate between wholesome and deleterious food. This
function is, of course, not to be neglected, especially if due credit be
given to the rôle played by smell in the same service. It is however
true that, although the indications of taste and smell may be, for lower
forms of animal life, fairly trustworthy guides in the selection of
edible substances, such criteria as taste and odor can by no means be
relied on by human beings. In a general way it is, of course, true that
wholesome substances possess taste qualities which are agreeable and
enjoyable, while foul, decaying and poisonous substances are often
characterized by tastes and odors that arouse in us disgust and
revulsion.

But in the complex lives of human beings, at least, this sort of natural
adaptation is far from adequate to constitute a dietetic guide. Not only
is it true that many substances accessible to human beings are injurious
and unwholesome, in spite of their agreeable taste; it is equally true
that many substances that are initially distasteful may be either
nourishing or remedial. Human beings find it necessary to supplement, or
even to supplant, the “beneficent guardianship” of taste by the
introduction of various other sources of information and criteria of
selection.

We do not find, however, that the sense of taste shows any evidence of
deterioration as the result of such loss of function. Probably never
before in the history of our race has there been such diligence and zeal
in ministering to the demands and satisfactions of our appetite. In the
preparation, marketing, and serving of food the appeal through
tastefulness and flavor stands second only to that through purity and
cleanliness. The situation is neatly stated by Jane Addams in the
following words: “Perhaps the neighborhood estimate (of their New
England kitchen) was summed up by the woman who frankly confessed that
the food was certainly nutritious, but that she didn’t like to eat what
was nutritious; that she liked to eat ‘what she’d ruther.’”

It is clear at once that the satisfactions of taste are pursued, either
secretly or openly, for their own sake, and often in obvious disregard
of their dietetic consequences. Shall we dismiss this pursuit as only an
instance of the search for pleasure in its own right or wrong, or is
there to be discerned a further function of taste experiences quite
aside from their guidance to eating, their warning of danger, and their
immediate sensory pleasure?


                         _Taste and Digestion_

Recent studies of the rôle of taste in the economy of the organism show
very decidedly that such an additional function, and a very important
one, must be recognized. These investigations have revealed the fact
that the pleasurable taste of food (along with its agreeable odor and
appearance) is responsible for the initiation of the first stages of the
process of digestion. Further, they have shown that disagreeable tastes
and odors (along with pain, fear, and other emotional excitement) may
effectually retard or even completely inhibit these very important
processes. Not only does the mouth “water” at the smell, or sight, or
thought, of delicious morsels, but the stomach itself responds, in an
anticipatory fashion, to the taste of agreeable substances placed in the
mouth. That “good digestion waits on appetite” is a physiological fact,
as well as an ancient proverb.

In the middle of the last century two observers in Leipsic reported the
pouring out of gastric juice at the mere sight or smell of a favorite
food in the case of “a hungry dog which had a fistulous opening through
the body wall into the stomach.” More recently it has been
experimentally shown that similar flow of gastric juice follows upon the
tasting of agreeable food, even if the food itself is not allowed to
reach the stomach. So relevant are these findings to the point we are
now considering that the following summary, by Cannon, of the work of
Pavlow may well be quoted in detail:


                        _Experimental Evidences_

“The feelings or affective states favorable to the digestive functions
have been studied fruitfully by Pavlow, of Petrograd, through ingenious
experiments on dogs. By the use of careful surgical methods he was able
to make a side pouch of a part of the stomach, the cavity of which was
wholly separate from the main cavity in which the food was received.
This pouch was supplied in a normal manner with nerves and blood
vessels, and, as it opened to the surface of the body, the amount and
character of the gastric juice secreted by it under various conditions
could be accurately determined. Secretion by that part of the stomach
wall which was included in the pouch was representative of the secreting
activities of the entire stomach. The arrangement was particularly
advantageous in providing the gastric juice unmixed with food. In some
of the animals thus operated upon an opening was also made in the
esophagus, so that when the food was swallowed it did not pass to the
stomach, but dropped out on the way. All the pleasures of eating were
thus experienced, and there was no necessity of stopping because of a
sense of fullness. This process was called ‘sham feeding.’ The
well-being of these animals was carefully attended to; they lived the
normal life of dogs, and in the course of months and years became the
pets of the laboratory.

Pavlow showed that the chewing and swallowing of food which the dogs
relished resulted, after a delay of about five minutes, in a flow of
natural gastric juice from the side pouch of the stomach—a flow which
persisted as long as the dog chewed and swallowed the food and continued
for some time after eating ceased. Evidently the presence of food in the
stomach is not a prime condition for gastric secretions, and, since the
flow occurred only when the dogs had an appetite and the material
presented to them was agreeable, the conclusion was justified that this
was a true psychic secretion.”

In several cases necessary operations on human beings have permitted of
observations similar to these experiments on dogs. Thus, Richet, who had
opportunity to observe such a case, “reported that whenever the girl
chewed or tasted a highly sapid substance, such as sugar or lemon juice,
while the stomach was empty, there flowed from the fistula a
considerable quantity of gastric juice.” Another observer, Hornborg,
“found that when the little boy whom he studied chewed agreeable food a
more or less active secretion of gastric juice invariably started,
whereas the chewing of an indifferent substance, as gutta-percha, was
followed by no secretion.”

Carlson has reported numerous similar observations on an adult. In the
case of this man the sight, smell, or thought of food, even when he was
hungry, was inadequate to cause the gastric juice to flow. Moreover,
“the mere act of chewing indifferent substances, and the stimulation of
the nerve endings in the mouth by substances other than those related to
food,” caused no secretion. But a few minutes after the taste organs
were stimulated by edible substances it was seen that not only did the
flow of gastric juice begin, but the “hunger contractions” of the
stomach were inhibited. Further, the secretion of gastric juice in this
patient was clearly seen to vary with the palatability of the food. The
chewing of bread and butter yielded a smaller flow than did the
mastication of meat, and the flow was always greatest during the chewing
of desserts, or on occasions when the food was said to be “unusually
fine.” Oranges, of which the patient was especially fond, produced a
greater flow than did pies, puddings, and other fruits. Carlson, in
reporting these observations, says: “There is no question but that the
mastication of a palatable dessert at the end of a meal serves to
augment and prolong the appetite secretion of the gastric juice.”

In referring to such cases Cannon has concluded: “All these observations
clearly demonstrate that the normal flow of the first digestive fluids,
the saliva and the gastric juice, is favored by the pleasurable feelings
which accompany the taste and smell of food during mastication, or which
are roused in anticipation of eating when choice morsels are seen or
smelled. These facts are of fundamental importance in the serving of
food, especially when, through illness, the appetite is fickle. The
degree of daintiness with which nourishment is served, the little
attentions to æsthetic details—the arrangement of the dishes, the small
portions of food, the flower beside the plate—all may help to render
food pleasing to the eye and savory to the nostrils, and may be the
deciding factors in determining whether the restoration of strength is
to begin or not.”


             _The Function of Taste in the Organic Economy_

The preliminary nature of these anticipatory secretions of the digestive
juices is by no means an adequate measure of their ultimate importance.
Studies of the mechanism of digestion show that each stage, as it
occurs, either directly or indirectly, through its product, affords the
appropriate stimulus which evokes the following stage. Thus, continued
flow of gastric juice is provided for by the action of the preliminary
flow or its products on the walls of the stomach; and other juices, such
as the bile and the pancreatic, are in turn released by the action of
this continued flow.

The pleasurable sensations of taste are thus the initial stimulus to the
whole series of digestive processes. Even in the absence of hunger these
sensations seem potent to initiate the digestive mechanism. Among the
most interesting of recent physiological studies are those showing the
very great sensitivity of the important organic mechanisms, especially
those of secretion, to such experiences as shock, worry, fear, anger,
grief, excitement, and pain. All these factors tend to retard the
activity of the digestive system, while they may also be seen to
reënforce the activity of other mechanisms. As opposed to the effect of
these factors, pleasurable experiences connected with food serve not
only to guide the organism in its choice, but play an important part in
its effective appropriation and assimilation, through their action in
setting the digestive mechanisms in action, and in guaranteeing the
continuation of this action after the completion of the act of eating.

Music and dance, jest and general merriment, genial conversation and
cordial friendship, prosperity and individual success, fragrance, color,
bodily ease, and a clear conscience—these and all the other joys of life
play their part in promoting the bodily welfare of the organism.
Conspicuous and potent among these favoring influences are the
sensations of taste and the strongly toned feelings with which they are
so closely associated—“the satisfactions of the palate.” Even the
various “bitters” which are so commonly used as “appetizers” seem to owe
such efficacy as they may possess to the influence of their taste on the
preliminary flow of “appetite gastric.” Carlson has shown that these
bitters, introduced directly into the stomach in medicinal doses, have
no influence on the hunger mechanisms. In larger doses their effect is
inhibition of hunger. Acting in the mouth, they also retard the hunger
contractions of the stomach in proportion to their intensity as taste
stimuli. In so far, then, as “bitters” are “appetizing,” it is by virtue
of their taste qualities, rather than their medicinal properties, and
the act of swallowing them would seem to be superfluous.


------------------------------------------------------------------------



                              CHAPTER XIV

                      THE ÆSTHETIC VALUE OF TASTE


                     _The Higher and Lower Senses_


WHEN people are asked to state which are the higher and which the lower
senses they feel no hesitation in deciding. When asked to arrange the
various senses in an order of merit on this basis they are able to do so
promptly. Moreover, their various arrangements agree very closely with
each other. Vision commonly stands at the top of the series; then
hearing; touch and smell are given third and fourth places about equally
often; taste is likely to be next; and finally temperature, sensations
of movement, and the more general organic sensations. When asked to
state what meaning they give to the term “higher” in making this
arrangement there is more disagreement in the nature of the replies.
Occasionally an individual asserts that by “higher” he means more
elaborate, complicated,—“highly” differentiated. A few individuals mean
by “higher” more useful, indispensable,—“higher” in value. But by far
the larger number of individuals mean neither the one nor the other of
these two notions, but have in mind some characteristic which is not
immediately related either to structural complexity, genetic antiquity,
nor practical utility,—a characteristic which can only be described as
ethical or æsthetic.

Evidence of a cleavage of the senses on an ethical basis is abundant.
Quotations from Burton’s “Anatomy of Melancholy” may serve as
representative of statements that can easily be found in the writings of
all centuries, from the Socratic period, through the reflections of the
schoolmen, down to the modern textbooks of psychology. Says Burton:

“Of these five senses sight is held to be most precious and the best....
Hearing is a most excellent outward sense.... Taste is a necessary
sense.... Touch, the last and most ignoble of the senses, yet of as
great necessity as the others, and of as much pleasure.”

Contemporary phraseology and convention are just as eloquent in the
matter. There is common agreement that some of the senses, in their
exercise or consequences, are ennobling, dignified, pure, and worthy;
others, either in their exercise or consequences, are felt to be
degrading, debasing, vile, and iniquitous. An individual who revels in
impressions of sight and sound, and indulges to the utmost the raptures
afforded by the tones, melodies, concords, the colors and their
harmonies, and the elements of form, design, and arrangement, we are
likely to find classified by his associates as “sensitive,”
“temperamental,” “artistic.” But one who revels to the same or even much
less degree in the unholy impressions of contact, temperature, smell,
and taste is held to be “sensuous” rather than “sensitive,” “gluttonous”
rather than “temperamental,” and “vicious” rather than “artistic.” The
former pleasures minister to a “divine fire,” the latter only to “lust”
and “appetite.”

Similarly, we esteem in quite distinctive manner the workman whose craft
consists in the preparation and arrangement of sights and sounds in
pleasing elements, orders, and compositions. He is held to have
“acquired merit,” however unsuccessful his labors, and receives warm
social approbation. He is an “artist.” But the workman whose craft
consists in the preparation and presentation of acceptable sensations of
taste, smell, touch, and temperature, what of him? He is neither held to
have “acquired merit” nor to deserve any enviable amount of social
recognition. He is only a “cook,” a “chef,” or, at the most, a “chemist”
or a “dietitian.” Only in the comic supplements is he ever an “artist.”
Painting, for instance, is held to be an “art”; but cooking is only a
“service.” The one is rewarded by distinction and eminence, the other,
when rewarded at all, by wages.

In the field of æsthetics the distinction between the “higher” and the
“lower” senses is no less clear. Museums and galleries we have in
abundance in which are preserved and displayed the treasures of light
and shade, color and form, line and arrangement. Private and public
funds are appropriated in order that these impressions may have the
widest possible circulation. Visitors and classes throng the corridors
of these storehouses; teachers and schools flourish on the profits
derived from the communication and publication of the principles
concerned in their manufacture; statues are erected to the most
deserving craftsmen; and earnest apprentices starve in foreign garrets
in order that their handicraft may in time adorn these walls. Much the
same thing is true of pleasing arrangements of sound impressions. All
possible pains are taken to record the scheme and plan of their
production, and the heartiest welcome is accorded any device,
instrument, or organization which will facilitate their being stored up
and poured out again for the delectation of remote or future audiences.

But to what museum or gallery shall one go who longs to experience the
glorious array of pleasing contacts, textures and pressures, odors,
tastes, and temperatures? Where shall one find stored up representatives
of the most satisfying and thrilling touch impressions that experience
has ever yielded, the whole gamut of delectable odors, with all the
offensive ones left out; all the aromas and savors and flavors in which
the gustatory and olfactory world is so rich? And all the organic
thrills, the kinæsthetic whirls and starts, and the delicious
dizzinesses of static experiences? Coney Island and its brood are the
only institutions that even pretend to minister to those whose nature
yearns for these satisfactions, and Coney Island is supported neither by
philanthropic endowment nor by public appropriations. It is even said
that its joys are thought to be “vulgar” among certain classes of
people, whose passions run mainly toward sights and sounds.

There can be no doubt about it. Certain of the senses are more æsthetic
than others, if by this we mean that special arts have been built up
which busy themselves with the materials afforded by them. Certain of
the senses, again, are unæsthetic, in the sense that the materials
afforded by them have not yielded to that sort of structural
manipulation which constitutes the procedure of one of the “fine arts.”
And, furthermore, such manipulation as they do submit to is not only not
considered “fine,” but is designated by the negative term “unæsthetic”;
the materials themselves, as well as those who busy themselves with
them, are quite likely to be esteemed “coarse” and “nasty.”


            _Bounty of Nature and Ecclesiastical Censorship_

One may well inquire into the reasons for such a curious state of
affairs. Does it merely signify that agreeable sights and sounds are so
rare in nature that special social encouragement has come to be given
for their production, while pleasing contacts, pressures, tastes,
smells, etc., are so abundantly provided in the natural course of
experience that no such sanction is called for? Even if this were true,
does it follow that the sanction of the one group need necessarily
involve the taboo of the other? Does it perhaps merely indicate that
early in the history of art the Church and its leaders learned that the
original tendency of men and women to indulge themselves in the
voluptuous impressions of certain of the senses was so strong that the
immediate joys of earth promised to outweigh the promised blessings of
heaven? Such a discovery might well have resulted in an authoritative
denunciation of these types of experience and in an artificial
exaltation of the tamer and milder senses, whose objects could be
perceived at a remote distance and by many observers, and could be,
therefore, more minutely scrutinized by the ecclesiastic censors. Or
does it perhaps mean that some of these sense impressions from their
very nature are either unsuitable as materials for that sort of
manipulation and craftsmanship which we call artistic, or, from their
very nature or consequences, are inimical to and destructive of those
endeavors which we have come, on other grounds, to conceive to be the
most worthy and valuable tendencies of men and women? The bounty of
nature and the ecclesiastical censorship we may dismiss from the present
consideration, however worthy they may be of reflection, and confine our
present inquiry to the question of whether or not the impressions
afforded by some of the senses, such as taste, for example, are, by
their very nature, inadequate as raw materials of æsthetic manipulation
and artistic creation.


                    _The Psychophysical Attributes_

It may be well to begin our inquiry with a consideration of certain of
the technical psychological characteristics and properties of the
different senses, properties which can be measured and expressed in
quantitative terms. We may then observe whether their order, when
arranged on these bases, shows any correspondence to their order in the
scale of æsthetic value, and where, in such a scale, the sense of taste
belongs. The following table brings together the facts concerning four
of these characteristics. In the first column the senses are arranged in
the commonly accepted order of æsthetic value, and the degree of
correspondence can be easily made out by comparing this column with
those in which the various other properties are indicated.


 +——————+————————+———————+—————+——————+
 |            |                |              |          |  Average   |
 |  Order of  |   Number of   |              | Average   | Duration   |
 |  Æsthetic  | Discriminable   |Sharpness of   |Speed of   |    of a    |
 |   Value    |   Qualities     |Discrimination |Reaction   | Sensation,  |
 |            |                |              |          | Degree of  |
 |            |                |              |          |   Inertia   |
 +——————+————————+———————+—————+——————+
 |   Sight     |  About 40,000  | Difference    |.189 sec.   |   About    |
 |            |                |    of 1%     |          | .030 sec.  |
 +——————+————————+———————+—————+——————+
 |  Hearing   |   “   15,000   | Difference     |.146 sec.   |  About     |
 |            |                |    of 33%    |          | .002 sec.  |
 +——————+————————+———————+—————+——————+
 |            | Nine classes,  |              |          | Very long  |
 |            |   each with    | Difference   |Difficult |    and     |
 |   Smell    |  hundreds of   |    of 25%    |    to    | difficult  |
 |            |   qualities    |              |determine |    to      |
 |            |                |              |          | determine  |
 +——————+————————+———————+—————+——————+
 |            | Three or four  |              |          |            |
 |            | classes with   |   Difference   |          |  .001 to   |
 |   Touch    | qualities not  |     of 33%    | .149 sec. | .002 sec.  |
 |            |    easily      |               |          |            |
 |            |   determined   |              |          |            |
 +——————+————————+———————+—————+——————+
 |            |  Four classes  |              |          | Very long  |
 |            |  with number  |              |.300 sec.  |    and     |
 |   Taste    |   of qualities   |   Doubtful   |   to     |   difficult  |
 |            |      not       |              |1.000 sec. |    to      |
 |            |   determined   |              |          | determine  |
 +——————+————————+———————+—————+——————+
 |Kinæsthetic  | Four or five   | Difference    | Difficult | Undetermined|
 |(Movement,  | classes with   |    of 5%     |    to    |            |
 |Strain, etc.)  |   number of  |               |determine |            |
 |            |   degrees     |              |          |            |
 |            |     not       |              |          |            |
 |            |  determined   |              |          |            |
 +——————+————————+———————+—————+——————+
 |            |  Two classes,  | Variable and  | .150 sec. | Difficult |
 |Temperature |    difficult     |    to        |     to   |  to   |
 |            |    degrees     |to determine   | .180 sec | determine  |
 |            |not determined  |              |         |            |
 +——————+————————+———————+—————+——————+
 |  Organic   |   About six    |   Unknown   | Unknown | Unknown  |
 |            |    classes     |               |          |            |
 +——————+————————+———————+—————+——————+


It requires only a glance at this table to reveal the fact that we
possess much more definite knowledge about sight and hearing in these
respects than we do about the other modes of sensation. In the case of
these two senses, the four characteristics indicated in the table can be
stated with considerable precision and certainty. But in the case of the
other senses, and of taste in particular, only broad and vague
statements can be made, for the most part. Even the number of
discriminable qualities which these senses afford is unknown, and
statements concerning the other properties are mainly confessions of
difficulty or ignorance. It is difficult to judge to what degree this
state of affairs is due simply to the greater attention that has been
given to sight and hearing in precise psychological investigation, and
to what degree it is due to difficulties inherent in the nature of the
sense impressions afforded by the other modes. Nevertheless, it is
apparent that no one of the special characteristics indicated in the
table can be held responsible for the sharp cleavage commonly made
between the worthy and the ignoble senses. Consideration of the
characteristics in detail shows that we must look elsewhere for the
reasons why the lower senses are unæsthetic, and even, perhaps, for the
reasons why they are lower.

With respect to number of discriminable qualities, for instance, sight
and hearing, with their many thousand distinguishable degrees of
impression, might seem to afford such an abundance of raw material that
this alone would explain why the principal fine arts have come to be
based on these senses. But it must be pointed out that this enumeration
of qualities has reference only to the definitely identifiable,
classifiable, and controllable degrees of impression. The mere fact that
odors can be classified under only nine headings, to which general terms
can be given, does not at all mean that there are but nine
distinguishable smells. Almost every different object in the world has
its own characteristic odor. We have not developed abstract names for
these odors, to be sure. We are usually content to designate the odor by
the name of the object with which it is associated. And when one bears
in mind the multitudinous variations of these odors, their different
intensities, mixtures, and modifications, one is inclined to believe
that it is only the infinite variety of smell experiences that prevents
our enumerating, classifying, and designating them. And what has just
been said of smell is equally true of touch, taste, and organic
sensations. It is also true that the separate lower senses are seldom
stimulated independently,—thus taste is always accompanied by smell,
touch, temperature, etc. May it perhaps be true that the very fact that
these impressions cannot be estimated, isolated, and reproduced at will
has something to do with their inferior æsthetic value? However this may
be, it is clear that the mere variety of impressions afforded is not the
criterion of which we are in search.

One might be tempted to suppose that the sharpness of discrimination of
the various senses, the keenness with which differences in the strength
and intensity of impressions can be detected, might be an important
factor in determining their availability for æsthetic manipulation. The
figures given in the table under this heading indicate the proportion
that must be added to a stimulus in order to make it just perceptibly
more intense. The temptation is removed at once by a mere inspection of
the values. Sight is, to be sure, the most delicate of the senses in
this respect, as it is also in number of isolable qualities. But
kinæsthetic sensation follows close upon it, while smell stands third in
the list, and hearing is no more sensitive than pressure. In the case of
taste and the other senses the values are unknown or difficult to
determine, but it is clear that the æsthetic values of the different
senses do not depend merely on their various psychophysical constants.

The quickness with which one can react to or perceive impressions from
the various senses discloses much the same state of affairs. Basing our
comparison on the average reaction times to the most commonly available
impressions and intensities in each case, hearing, touch, and
temperature are seen to be about equally prompt, while sight stands
fourth on the list. With respect to the period of time through which a
sensation continues to persist, the so-called “life span” of an
impression, only three of the values, those for sight, hearing, and
touch, have been determined, and these bear no significant relations to
each other. But these times are all very short, and the corresponding
modes of sensation stand high in the æsthetic scale. The other values,
although not determined, are known to be much longer than these. Is it
possible that the sluggishness of these senses and the persistence of
impressions once set up through them is so great that the impressions do
not submit to the forms, patterns, and structures which constitute
artistic treatment? Or may it not be equally true that the fugitive
character of impressions from the higher senses is what has made
necessary the development of treatment by means of pattern and
structure?


                      _The Tendency to Adaptation_

Suggested by this question of “life span” of sensations is another
characteristic which one might expect to find important,—viz., what we
have in an early chapter referred to as the “tendency to adaptation” of
the different senses. In the case of odors, temperatures, and contacts,
we easily and speedily become adapted to continuous presence of
impressions and cease to be aware of their existence. Thus, we soon
become adapted to the presence of hats on our heads, the clothes on our
backs, the smell of smoke, and even to such extreme temperatures as that
of the stoking room. Continuous stimulation of one of these senses so
raises the threshold of the sense organ that the original stimulus
ceases to be effective. So far as practical and æsthetic purposes are
concerned, we are then fatigued to the particular impression. We may be
gratified to find that this tendency to adaptation is not nearly so
conspicuous in the case of sight. But we will be equally dismayed to
learn that the tendency is as prominent in the case of hearing as it is
in the so-called lower senses. Moreover, this tendency refers to
continued stimulation of the same degree or quality, whereas in æsthetic
manipulation the qualities presented are varied from moment to moment
and from point to point.


                _Spatial Attributes of Taste Qualities_

On the whole, then, these strictly psychological or psychophysical
comparisons are so unsatisfactory that we are compelled to look
elsewhere for the criteria of the raw material of æsthetics. Some
writers have suggested that the absence of definite and formal spatial
attributes and systems is what makes certain of the senses unsuitable
for æsthetic treatment. But there are two important objections to this
suggestion. One is our earlier question as to the reasons why æsthetic
treatment should necessarily consist of arrangement in spatial and
temporal series and patterns. Unless some excellent reason to the
contrary is given, we are free to assume that this is not a necessity,
but merely an incidental result, following from the character of the
materials, which, for other reasons, for which we seek, are chosen as
the raw materials for æsthetic treatment. The other objection, which is,
perhaps, more convincing, is the fact that, whereas touch and
kinæsthetic impressions both possess immediate voluminousness and take
their place readily in a spatial manifold of position, direction,
distance, and form, they do not yield to æsthetic treatment; while sound
and taste, one of which easily ranks second and the other of which
belongs low down in our æsthetic scale, possess extent in only a very
doubtful and probably analogical manner, and are almost, if not wholly,
lacking in those qualities which would enable them to participate in a
manifold of position, direction, distance, and form. As for temporal
attributes, such as duration and sequence, all impressions possess them,
from whatever sense they originate. The idea that the difficulty or
impossibility of giving spatial and temporal form to the lower
sensations prevents the representation of nature by means of them, and
that this is a sufficient reason for regarding them as inferior is
anything but adequate.


                  _Immediate Affective Value of Taste_

Perhaps the greatest surprise comes when we consider the immediate
affective value of impressions from the different senses. Impressions of
taste, smell, and contact bear with them or immediately provoke very
definite and powerful feelings,—feelings of pleasantness and
disagreeableness, excitement and calm, tension and relief. Still more
complex emotions than these simple feelings are called up more easily
and universally by impressions from these senses than in any other way.
Their immediate pleasure tone and their associated emotions may be, and
usually are, exceedingly rich and intense. The smell of new-mown hay,
coffee, flowers, whiffs of the salt sea breeze, the odors of animals,
foods, spices, and herbs move us to strong emotions. The stroking of
fur, the cool of evening, the delicious languor of a sun bath—all these
have high and immediate affective value that can hardly be exceeded by
any emotions provoked by colors, forms, noises, and tones. In general,
those senses that are closely connected with our personal and bodily
welfare, as is the case with taste, provoke strong affective reactions
and convey to us a strong sense of reality. Those senses which are much
less intimately related to our immediate bodily welfare possess much
weaker feeling tone and provoke much less emphatic emotional reactions.
Disagreeable odors, tastes, and contacts are quite beyond our endurance,
but few are the sights and sounds to which we cannot easily reconcile
ourselves. Here, then, we have the interesting and perhaps unexpected
fact that the sense impressions possess æsthetic value just to the
degree that they fail to arouse in us definite and powerful feelings.
The inverted arrangement on the basis of æsthetic value gives us
precisely the order on the basis of immediate affective value.
Santayana’s assertion that the small range and variety of pleasure-toned
qualities among the lower senses explains their non-æsthetic character,
in part, is seen to be not only inadequate, but even a perversion of the
facts. Just in that degree to which sense impressions fail to produce in
us immediate pleasures and aversions, fail to provoke us to instinctive
emotions of joy and disgust, fail to stir in us moods of irritation and
acquiescence,—in just that degree do they declare themselves to be
adequate raw materials for the fine arts. If, as we are often told, the
primary purpose of art is to please, this must be an entirely unexpected
state of affairs, and the low position of taste in the æsthetic scale
becomes quite unintelligible.


              _Development in the Individual and the Race_

Perhaps this is as appropriate a place as any in which to point out that
the order of the senses, on the basis of their æsthetic value, is
approximately that of their philogenetic and ontogenetic development.
The simplest and most undifferentiated forms of animal life possess, in
more or less rudimentary form, sensitivity to impressions which must
resemble closely what we know as contact, pressure, movement, and
temperature. Touch, as Aristotle tells us, is the “mother sense.”
Starting from this form of sensibility as a basis, the other senses
develop as we ascend the animal series, by processes of increasing
complexity and refinement. Taste and smell, as we know those
experiences, were probably the next to differentiate themselves from the
vague mass of tactual and organic sensation, then hearing, and last of
all sight. And there is evidence of sequence within a single sense; thus
it would appear that brightness vision, sensibility to mere light and
shadow, antedated color vision by a considerable interval, and even that
sensibilities to the various color impressions developed in some sort of
serial order. It is also true that the sense organs upon which fall the
stimulations of the physical world are, at the birth of the individual,
in very diverse conditions of functional perfection. The nerves which
underlie sensations of taste, touch, temperature, and pain operate
perfectly at birth. Hearing is defective for one to two weeks after
birth, and the mechanism of vision is still more imperfect and commonly
remains so for several weeks. From the point of view of the three
meanings of the word “higher,” the ethical, the æsthetic, and the
genetic, the order of the senses is the same. Such close agreement
cannot be entirely without significance.


                    _The Imaginative Value of Taste_

A further characteristic which correlates closely with the æsthetic
arrangement is to be found in the relative ease with which images can be
called up and contemplated in the various modes of sensation, in the
absence of any physical stimulation,—what we may call the imaginative
possibilities of the different senses. With most people visual and
auditory imagery is both more vivid and intense, and more facile and
prompt, than is imagery within any of the other sensory modes. We have
in another section referred to one observer who recorded his mental
images as they occurred or were noticed until 2,500 had been enumerated,
and who reports that 57 per cent of them were visual, 29 per cent
auditory, leaving only a total of 14 per cent for images from all the
other senses. Dreams, which consist mainly of imagery experiences, are
commonly visual in character, with hearing a close second, and the other
modes hardly represented at all. Hallucinations reported by supposedly
normal people are in 90 per cent of the cases either visual or auditory,
and the visual are about twice as frequently reported as the auditory.
Records of hallucinations among the insane show vision and hearing
clearly most prominent, with hearing somewhat more prominent than sight.
Can it be that the possibility of recall in the form of imagery,
contemplation in the absence of the original stimulus or object, is one
of the prime qualifications of sensory impressions that are to serve as
æsthetic material? There will probably be no exception taken to such a
generalization on the part of anybody. The order on the basis of
imaginative value is identical with that on the basis of æsthetic value,
ethical value, and genetic development.


             _The Non-Social Character of the Lower Senses_

It is interesting to note that the higher senses are also the so-called
distance receptors; they do not require immediate contact with the
stimulus-producing object, whereas the lower senses inform us mainly
concerning objects that are in direct or approximate contact with our
own body. By virtue of this fact, as has often been remarked, it is
possible for many of us to _see_ the same object, such as a rainbow,
however far apart we may be from each other. And we can all hear the
same melody-producing instrument if we place ourselves within a certain
fairly large area. But social experience is scarcely possible in the
case of contact, taste, smell, temperature. Here the most we can do is
to get the experiences in succession, and even this is often impossible.
Even when it is possible to get the experiences in this way, by taking
turns, we find it difficult to confer over them, since all conference is
now on the basis of memory images, and, as we have already seen, we find
it difficult, if, indeed, not quite impossible, to call up clear and
persistent images of the impressions afforded by these senses.

It is true of some of these senses that in their enjoyment the stimulus
itself is consumed. Whenever this is the case the sense concerned will
be found to be one of the so-called lower, unæsthetic senses. Not only
is social experience of the enjoyable object impossible, but even the
single individual cannot himself get the experience again. Can it be,
perhaps, that, as Thorndike remarks, “the pleasures of taste are not
called æsthetic because one cannot eat his cake and have it, too”? It
begins now to look as though only those sense impressions can become
æsthetic vehicles which somehow lead beyond themselves, and beyond the
immediate gratification of the individual, and facilitate some sort of
social operation, or conference, or participation. In saying this we do
not have reference to the doctrine that one often hears
emphasized,—viz., that the lower senses, such as taste, are low and
unæsthetic because they minister mainly to our personal and
physiological needs. Nothing could be farther from the truth. It is not
because taste, smell, and touch are mainly concerned in telling us of
facts that are of fundamental vital importance to us as individuals that
they are low or unæsthetic, but only because they do nothing more than
this,—because they cannot become the vehicle of our individual and
social conference and communication.

In this connection let me quote an illuminating comment from Miss
Calkins’ chapter on “Perception” in her “Introduction to Psychology.” As
she there writes:

    “It thus appears that even perception, the consciousness, as we
    call it, of outer things, is a consciousness of other selves as
    sharing our experience, a relatively altruistic, not an
    exclusively egoistic mode of consciousness. This is the reason
    why we usually speak of sight and hearing and smell as higher
    senses—and in the order named—than taste and the dermal sense
    experiences. Vision is the sense most readily shared by any
    number of selves: for example, everybody within a very wide area
    may see the mountain on the horizon or the Milky Way in the
    evening sky. Next to vision, sounds are the most frequently
    shared experiences; millions of people hear the same thunder and
    thousands may share the same concert. Even odors, though shared
    by fewer people, may be common to very many, whereas tastes and
    pressures and pains, which require actual bodily contact, and
    warmth and cold, whose physiological stimulation depends on
    conditions of the individual body, are far less invariably
    shared experiences. But the shared experiences are those that
    are described, discussed, repeated, measured—in other words,
    those that are creatively reëmbodied in works of art and in
    scientific investigations. Vision, therefore, is a higher sense
    than the others, only in so far as it is more often shared, and
    hence more often discussed and described, measured and verified.
    This is the reason why it is a more significant social material
    of intercourse, art, and science. Pressure and warmth, on the
    other hand, are less valued, because they are less often
    actually shared and, therefore, less easily verified and less
    frequently described.”

This, we have said, is an illuminating paragraph. But it is satisfactory
only when amplified in certain ways to which we seem to have been led in
our preceding discussion. Thus, it cannot be said that the socially
shared sense impressions are chosen as the raw material of the fine arts
merely because they enable a multiplication of individual pleasures. The
dominant passion of the artist is not merely to afford pleasure to the
greatest possible number of observers. But so long as art is defined as
an attempt to please, that is about all that follows from the social
character of the higher senses. As a matter of fact, artists do not seek
to please the greatest possible number of observers. They are often
contented if a single observer is satisfied. And by satisfied, in this
connection, one does not mean pleased. We have already seen that the
most pleasing of all sense impressions are those afforded by the lower
senses. If the mere production of pleasure is the chief aim of the
artist, he would surely have resorted to those materials which in
themselves and by their own direct effects facilitated his purpose.


            _The Unsystematic Relations of Taste Qualities_

Another characteristic of those sense materials which enter into art
products,—especially vision and hearing,—is the fact that the various
experiences constituting the sense manifold exhibit structural and
systematic relationships. We do not here refer to the possibility of
spatial arrangement and form. This we have already discussed and
dismissed as an inadequate criterion. We mean, rather, those facts
represented, in the case of vision, by the color pyramid and similar
schemes for representing the qualitative relations of visual sensations;
and, in the case of sound, by the tonal scale and such graded intensity
scales as may be devised. Definite and formulable relations with respect
to such facts as fusion, harmony, tonality, and melody; saturation,
contrast, complementariness, mixture, etc., may be made out in the cases
of vision and hearing. Æsthetic manipulation takes the form of playing
upon these relationships. The visual and auditory qualities constitute
not merely a manifold, but yield systematic structures. But the sense of
taste and the other lower sensation modes tend to constitute a mere
unorganized manifold.

Now, it may be at once suggested that we here have the adequate
criterion of the æsthetic for which we are searching, and that this is
at bottom the reason why it is the visual and auditory experiences that
are “described, discussed, repeated, and measured (and) creatively
reëmbodied in works of art.”

But even this account is, as a matter of fact, very one-sided and in
part, at least, fallacious. We do not know what structural systems would
be exhibited by the lower sense experiences if we had only discussed
them, measured them, and creatively embodied them to the degree to which
we have gone in the case of the higher senses. We cannot be sure, in the
present state of our knowledge, to what degree the appearance of
superior organization on the part of the higher senses is due to the
amount of effort and inquiry we have bestowed upon their examination.
All that we really know is that innumerable studies have been made of
sight and sound, and that we are able to represent their results in the
form of schemes and systems; whereas, comparatively few studies of the
intensive type have been made of the various “lower senses,” and we are
proportionately unable to construct the corresponding schemes and
structures. Which is cause and which is effect? Do the lower senses fail
to provide the raw materials of æsthetic construction because of their
lack of elaborate and systematic organization, or do they owe this very
deficiency to the relative neglect they have suffered at the hands of
the artist?


                   _The Motive of Æsthetic Products_

There is some further reason why the æsthetic sense impressions are
those which are genetically most recent, in imagination the most capable
of clear and persistent revival, pertaining mainly to the distance
receptors, informing us of objects which may be socially shared, and
capable of systematic and organized description. It seems that this
reason is simply that the main thing about an æsthetic presentation,
arrangement, or composition is, after all, its intellectual content, its
“message.” The artist desires, above all, to eliminate our own immediate
and instinctive reactions to his materials. In so far as he is an
artist, he is not satisfied with presenting to us a pleasing array of
sense materials. His main concern is in communicating to his observers
some situation, some theme, some state of affairs, some meaning, some
purely relational fact. Such emotions as are stirred in us he does not
wish to come from his mere materials, but from his own manipulation of
them, from the form or pattern which he gives them, from the meaning
which he thereby conveys to us. The true artist, in other words, is
neither a chemist, nor an athlete, nor a technician of any sort
whatsoever, but a philosopher.

Stout makes a similar comment when he says: “The distinction between
what we call the higher and lower senses rests on this contrast between
the intrinsic impressiveness of sensations and their value for
perceptual consciousness.... The relatively higher senses deserve this
title in proportion as they are more delicately discriminative and more
capable of being combined in successive and simultaneous groups and
series, while preserving their distinctive differences. On the other
hand, each several sensation is proportionately less important through
its own intensity and pleasant or painful character. Any direct effect
produced by its own intrinsic intensity and affective tone would
interfere with its value as a vehicle of meaning—as an indication of
something beyond its own existence. Thus, as perceptual consciousness
becomes relatively more prominent and important, sensation is more
delicately differentiated, more definitely restricted, less intense, and
less strongly toned in the way of pleasure and pain.”

The comments one is offered in the books on “art,”—eulogies of Raphael’s
rich color tones, Rembrandt’s lights and shadows, Rubens’ flesh tints,
Meissonier’s minute details, Turner’s accurate reproduction of ferns and
mosses, smoke and fog, and so on, represent a deliberate degradation of
the work of the artist to the level of cookery, the manufacture of
perfumery, dye-stuffs, and the operation of merry-go-rounds. It is
crediting the artist with just that result which æsthetic manipulation
has always sought not to produce,—the presentation of sense materials,
which of their own right awaken strong feeling tone in the observer.
When George Frederick Watts attempted, beyond those before him, to
convey meaning through his arrangements of sense impressions he refused
to attend minutely to the details of technique, and critics subsequently
said of him, “His technique is faulty.” Perhaps it was, but that is the
sort of comment one passes on an athlete, a ventriloquist, or a juggler.
One might just as significantly criticize the literary style of a
mathematician or a logician as the technique of an artist. Such
criticisms, to be sure, have a legitimate place in life. But the critic
of the mathematician’s literary style should not delude himself into the
belief that he is discussing mathematics, nor the critic of the artist’s
technique fancy that he is dealing with his art. For the real artist is
a philosopher, and that is the reason why the lower senses are
unæsthetic.


------------------------------------------------------------------------



                                 INDEX


 Abnormalities, of taste, 97, 123 ff., 151 ff.

 Acetate of lead, 4

 Acid, 5

 Adaptation, phenomena of, 48
   tendency to, 180

 _Addams_, 159

 Æsthetics, motive of products, 192

 Æsthetic value, of the senses, 168 ff.

 Affective value, of sensory qualities, 182 ff.

 After images, nature of, 37
   of taste, 39

 Ageusia, 152

 Alkaline, taste, 20

 Alkaloids, taste of, 5

 Allotriophagia, 157

 Annelids, sense organs of, 133

 Antagonism, of colors, 30
   of tastes, 31

 Appetite, 164 ff.

 Apple, taste of, 13

 Areas, of taste, 23, 75

 Art, and philosophy, 194

 Auræ of taste, 151


 _Bailey_, 45

 _Bain_, 8

 _Bell_, 134

 Birds, senses of, 140

 Bitter, 5, 7, 20, 21, 22, 31, 36, 40, 45, 47

 Blends, of taste, 18, 29

 _Boyle_, 110

 Brain center, for taste, 89 ff.

 _Brown_, 150

 _Burton_, 169


 _Calkins_, 189

 Camphor, taste of, 12

 Cane sugar, taste of, 4

 _Cannon_, 161

 _Carlson_, 163

 Cells, supporting and gustatory, 80, 108

 Censorship, 173

 _Chatin_, 7, 18

 Chemical sense, 131, 135 ff.

 Chemistry, 1, 4, 78, 96, 99

 _Chevreul_, 4, 12

 _Chinaglea_, 58

 Chloroform, taste of, 4, 13, 76

 Chorda tympani, 87, 98

 Classification, of tastes, 3 ff.
   of papillæ, 70
   of taste stimuli, 96

 Cocaine, 21

 Coffee, taste of, 13

 Colloids, 5, 94, 110

 Colors, primary, 2
   names of, 24
   organization of, 27

 Compensation, in colors, 30
   in tastes, 31

 Contrast, experience of, 34
   laws of, 37

 Crustacea, sense organs of, 134

 Crystalloids, 5, 94, 110

 _Cushing_, 88


 Development, of taste, 51 ff., 116 ff., 143, 184

 Digestion, and taste, 160

 Discrimination, of tastes, 47
   sharpness of, 175

 Dreams, and taste, 124, 149, 186

 Drugs, effect of, 20, 150

 Duration, of sensations, 175


 Electric stimulation, 100

 Evolution, of senses, 52
   of taste, 53, 116, 128 ff., 184

 Eye, as sense organ, 9, 60
   stimulus for, 111


 Fatigue, 48

 Fishes, senses of, 136

 Flat worms, sense organs of, 132

 Flavors, 18, 158 ff.

 Foods, taste of, 16, 31
   and flavors, 158

 _Forel_, 135

 Fusion, of colors, 2
   of tastes, 9, 18


 Ganglion, nature of, 85
   Gasserian, 86

 Gastric juice, 161 ff.

 _Gley_, 111

 _Graham_, 94, 110

 _Guezer_, 53

 Gymnema, 21


 _Haller_, 8

 Hallucinations, of taste, 124, 149, 151

 Heat, sensation of, 2

 _Hering_, 113

 _Herrick_, 137

 _Hornborg_, 163

 _Humboldt_, 101


 Imagination, and taste, 144 ff., 185

 Individual differences, 46, 122 ff.

 Inertia, of sense organ, 55

 Insects, senses of, 135


 _Kiesow_, 23, 30, 40, 41, 56, 75, 95, 99, 122

 Kinæsthesis, 9, 10, 19, 34

 _Kroner_, 53

 _Kuelpe_, 41

 _Kussmaul_, 53


 _Ladd_, 18, 41

 Lemonade, taste of, 29

 _Linnæus_, 8


 Magnesia, taste of, 5

 Malacia, 156

 Mammals, senses of, 141

 Manifold, of sensations, 2
   of taste, 3, 17

 Meats, taste of, 16

 Medusa, sense organs of, 132

 Memory, and taste, 144

 Mental images, nature of, 144
   of taste, 146
   classification of, 148

 Mixture, of tastes, 28

 Mode, of sensation, 7

 Motive, of æsthetic products, 192

 Muscles, of tongue, 66

 _Myers_, 23


 _Nagel_, 73, 76, 94, 97, 122, 125

 Names, of tastes, 23 ff.

 Nerves, of taste, 80, 83 ff., 115

 Neurone, nature of, 82, 85

 _Nichols_, 45


 _Oehrwall_, 114

 Onion, taste of, 13

 Organization, of taste, 27 ff., 190


 Palate, sensitiveness of, 75

 Papillæ, stimulation of, 10, 22
   sensitiveness of, 22
   location of, 68
   varieties of, 70
   function of, 105
   development of, 117

 _Parker_, 133, 138

 Parorexia, 156

 _Patrick_, 15

 _Pavlow_, 63, 161

 Perception, nature of, 29

 Periodic law, 5

 Perversions, of taste, 156

 _Peterson_, 53

 Philosophy, and art, 194

 Pica, 157

 Potassium, taste of, 5

 Primitive peoples, 23, 126

 Psychology, and classification, 6, 18

 Psychophysical attributes, 174 ff.


 Qualities, of taste, 1
   distribution of, 21
   of different senses, 175

 Quinine, taste of, 13, 22, 32


 Race differences, 126

 _Rainey_, 53

 _Ramsay_, 111

 Reactions, instinctive, 11
   time of, 56, 175

 Reptiles, senses of, 139

 _Richet_, 111, 163


 Saliva, flow of, 64, 93

 Salivary glands, activity of, 62
   function of, 103

 Salt, 5, 20, 22, 31, 36, 40, 45, 57

 Sapidity, conditions of, 93 ff.

 Schema, of color qualities, 27
   of tones, 28
   of tastes, 39

 Sense organ, of taste, 60 ff., 75
   development of, 116, 129

 Senses, higher and lower, 168 ff.
   æsthetic value of, 168 ff.
   of lower animals, 132 ff.
   development of, 132

 Sensitiveness, of taste, 43, 53, 99

 Sensitiveness, of tongue, 21, 99
   measures of, 43
   varieties of, 44
   of taste and smell, 46
   of the cell, 130

 Sham feeding, 162

 _Sheldon_, 138

 Smell, sense organ of, 11
   self-sacrificing character of, 14
   loss of, 15
   function of, 17
   names for, 24
   sensitiveness of, 46
   adaptation to, 49

 Social character, of senses, 187

 Sour, 5, 20, 21, 22, 31, 36, 40, 45, 57

 Spatial attributes, 181

 Specific energy, of taste nerves, 115

 _Stahr_, 117

 _Sternberg_, 96, 112

 Stimulus, meaning of, 3
   adaptation to, 48, 51
   adequate and inadequate, 92
   for taste, 92 ff., 111

 Subjective tastes, 149

 Sugar of lead, 5

 _Sulzer_, 100

 Sweet, 5, 7, 20, 21, 31, 36, 40, 45, 57


 Taste, acquirement of, 50
   adaptation to, 49
   æsthetic value of, 168
   agreeableness of, 7, 24, 50, 158
   biological rôle of, 158
   blends of, 9, 18, 28
   classification of, 3 ff.
   contrasts of, 37
   development of, 49, 116, 128 ff., 184
   disorders of, 123 ff.
   distribution of, 21, 73, 75, 123
   in lower animals, 128 ff.
   names for, 23
   organ of, 60
   organization of, 27 ff.
   poverty of, 14
   qualities of, 1
   sensitiveness of, 43, 53
   stimulus for, 92 ff., 105

 Taste buds, characteristics of, 78
   structure of, 79, 82
   function of, 107, 114

 Temperature, effect of, 58, 99

 _Thorndike_, 188

 Threshold, of taste sensation, 44

 Time, relations, 55
   of reaction, 57

 Tongue, as sense organ, 9, 21, 61, 120
   structure of, 65
   movements of, 67, 103, 105
   function of, 103

 Touch, sense of, 9, 12, 19


 _Valentin_, 45

 Vegetables, taste of, 16

 Vocabulary, of taste, 23

 _Volta_, 101


 Water, taste of, 150

 _Woodworth_, 18, 41

 _Wundt_, 8, 41, 142


------------------------------------------------------------------------



 ● Transcriber’s Notes:
    ○ Missing or obscured punctuation was silently corrected.
    ○ Typographical errors were silently corrected.
    ○ Inconsistent spelling and hyphenation were made consistent only
      when a predominant form was found in this book.
    ○ Text that was in italics is enclosed by underscores (_italics_).





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