.dt The Sense of Taste, by H. L. Hollingworth--A Project Gutenberg eBook
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THE SENSE OF TASTE
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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
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[Illustration: Publisher’s Logo]
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NEW YORK
MOFFAT, YARD AND COMPANY
1917
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Copyright, 1917, by
MOFFAT, YARD AND COMPANY
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Published April, 1917
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To
L. S. H.
AND
F. K. P.
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EDITORIAL INTRODUCTION
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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
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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
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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.
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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
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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.
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The editor takes this first opportunity to invite
criticism of whatever trend, and to ask for suggestions,
whether from sense-gluttons or from
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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.
.rj
G.V.N.D.
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Cambridge, Massachusetts,
January, 1917.
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PREFACE
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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.
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“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
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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
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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
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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.
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CONTENTS
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.ta r:7 h:40 r:6
CHAPTER | | PAGE
| Editorial Introduction | #vii#
| Preface | #xiii#
I | The Qualities of Taste
\
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. | #1#
II | The Organization of the Tastes
\
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. | #27#
III | The Sensitiveness of Taste
\
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. | #43#
IV | Time Relations of Taste Qualities
\
The Inertia of the Taste Organs—Reaction\
Time to Taste Stimuli—Determinants\
of Reaction Time to Taste. | #55#
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V | The Sense Organ of Taste
\
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. | #60#
VI | Sensory Elements of the Taste Mechanism
\
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. | #78#
VII | Taste-Producing Substances
\
Adequate and Inadequate Stimuli—Adequate\
Taste Stimuli—Inadequate Taste Stimuli. | #92#
VIII | The Function of the Taste Mechanism
\
The Function of Tongue and Salivary\
Glands—The Function of the Taste Buds. | #103#
IX | The Development of Taste in the 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. | #116#
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X | Evolution of Taste
\
Sensitivity of the Unicellular Organisms—“The\
Chemical Sense”—Chemical Sense\
in Fishes—Land-Dwelling Animals. | #128#
XI | Gustatory Imagination and Memory
\
The Nature and Frequency of Mental Images—Mental\
Images of Taste—Taste in\
Dreams and in Hallucinations. | #144#
XII | Unusual and Abnormal Taste Experiences
\
Gustatory Hallucinations and Auræ—Partial\
and Complete Ageusia—Taste Hallucinations\
of the Insane—Synæsthesias of\
Taste—Perversions of Taste. | #151#
XIII | Food and Flavor
\
The Biological Rôle of Taste—Taste and\
Digestion—Experimental Evidences—The\
Function of Taste in the Organic Economy. | #158#
XIV | The Æsthetic Value of Taste
\
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. | #168#
| Index | #197#
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ILLUSTRATIONS
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Diagram showing relations between the taste qualities | #40:i040#
Sketch of the tongue | #69:i069#
Diagram showing some of the various courses which\
have been advocated for the taste fibers in man | #88:i088#
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THE SENSE OF TASTE
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CHAPTER I||The Qualities of Taste
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The Taste Manifold
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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.
.pi
Is it then possible, in the field of our sensations,
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to reduce to elemental categories or units
the manifold[#] 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.
.pm fn-start // A
By a “manifold” is meant a great variety of objects or
experiences organized into one system or constituting one
field.
.pm fn-end
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
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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.
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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[#] 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,
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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.
.pm fn-start // A
By a “stimulus,” in this connection, is meant any object,
force, or agent that acts upon a sense organ.
.pm fn-end
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
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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[#] 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.
.pm fn-start // A
Resembling jelly or glue, uncrystalline in character.
.pm fn-end
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
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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
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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,
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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,[#] bitter,
sour, aqueous, and dry.
.pm fn-start // A
Styptic,—causing contraction of tissues.
.pm fn-end
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.
// p009.png
.pn +1
.sp 2
.h3
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.
// p010.png
.pn +1
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,
// p011.png
.pn +1
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
// p012.png
.pn +1
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
// p013.png
.pn +1
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
// p014.png
.pn +1
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.
.sp 2
.h3
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,
// p015.png
.pn +1
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
// p016.png
.pn +1
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,
// p017.png
.pn +1
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,
// p018.png
.pn +1
and why the final grant consists of these particular
four rather than others.
.sp 2
.h3
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
// p019.png
.pn +1
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,
// p020.png
.pn +1
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,
// p021.png
.pn +1
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.
.sp 2
.h3
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
// p022.png
.pn +1
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,
// p023.png
.pn +1
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.
.sp 2
.h3
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
// p024.png
.pn +1
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,
// p025.png
.pn +1
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
// p026.png
.pn +1
may be, they yield very little information
concerning the primitiveness, elementariness, sensitiveness,
or distribution of the various taste
qualities.
// p027.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER II||The Organization of the Tastes
.sp 2
.h3
System and Organization in Other Senses
.ni
.sp 2
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.
.pi
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
// p028.png
.pn +1
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.
.sp 2
.h3
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
// p029.png
.pn +1
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....
// p030.png
.pn +1
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.
.sp 2
.h3
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
// p031.png
.pn +1
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
// p032.png
.pn +1
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
// p033.png
.pn +1
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
// p034.png
.pn +1
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.
.sp 2
.h3
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
// p035.png
.pn +1
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
// p036.png
.pn +1
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
// p037.png
.pn +1
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.
.sp 2
.h3
After Images of Taste
Suggested by the phenomena of contrast are
the somewhat related facts of after sensations or
// p038.png
.pn +1
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
// p039.png
.pn +1
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.
.sp 2
.h3
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.
// p040.png
.pn +1
.if h
.il fn=i040.jpg w=600px id=i040
.ca
Fig. 1.
.ca-
.if-
.if t
.sp 2
[Illustration: Fig. 1.]
.sp 2
.if-
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.
// p041.png
.pn +1
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
// p042.png
.pn +1
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.”
// p043.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER III||The Sensitiveness of Taste
.sp 2
.h3
Various Measures of Sensitiveness
.ni
.sp 2
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
// p044.png
.pn +1
appear to have senses of exceeding acuteness,
although this may by no means be borne out by
actual measurements.
.pi
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.
.sp 2
.h3
The Threshold of Taste Sensation
Numerous investigations have concerned themselves
with the task of discovering the weakest
// p045.png
.pn +1
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:
.ta l:8 r:5 l:30
Sugar | 1.200 |parts to 100 parts of water
Salt | 0.300 |
Acid | 0.001 |
Quinine | 0.003 |
.ta-
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:
.ta l:8 l:12 r:18
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
.ta-
It is neither profitable nor interesting to draw
close comparisons between the various sets of
// p046.png
.pn +1
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.
.sp 2
.h3
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.
// p047.png
.pn +1
.sp 2
.h3
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
// p048.png
.pn +1
general statement can be made that, within limits,
increased strength of solution means increased
intensity of sensation.
.sp 2
.h3
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,
// p049.png
.pn +1
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
// p050.png
.pn +1
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.
.sp 2
.h3
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
// p051.png
.pn +1
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.
.sp 2
.h3
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
// p052.png
.pn +1
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
// p053.png
.pn +1
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
// p054.png
.pn +1
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.”
// p055.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER IV||Time Relations of Taste Qualities
.sp 2
.h3
The Inertia of the Taste Organs
.ni
.sp 2
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
// p056.png
.pn +1
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.
.sp 2
.h3
Reaction Time to Taste Stimuli
.pi
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
// p057.png
.pn +1
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:
.ta l:8 r:10
| Seconds
_
Salt |.307
Sweet |.446
Sour |.536
Bitter |1.082
.ta-
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:
// p058.png
.pn +1
.ta r:12 r:5 l:4
| Reaction to | Second |
_
sound | .146 |
touch |.149 |
sight |.189 |(?)
smell | .500 |(?)
.ta-
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.
.sp 2
.h3
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
// p059.png
.pn +1
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.
// p060.png
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CHAPTER V||The Sense Organ of Taste
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Comparison With Other Sense Organs
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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
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the other hand, only the receptor[#] 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.
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A receptor is the part of the sense organ in which the
transformation from a physical stimulus to a nerve impulse
occurs.
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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
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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.
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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
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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
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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,
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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.
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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
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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.
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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
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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.:i069#) 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.
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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.
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.ca
Fig. 2.
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[Illustration: Fig. 2.]
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.h3
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.:i069#), 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.
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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
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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
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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.
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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
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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
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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
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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
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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.
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.h2 id=ch06
CHAPTER VI||Sensory Elements of the Taste Mechanism
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Taste Buds and Their General Characteristics
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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
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of the taste mechanism have been reviewed, and
in this one we will describe the transforming
mechanism.
.pi
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
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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.
.sp 2
.h3
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
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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.
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.h3
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[#]
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,
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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.
.pm fn-start // A
Neurone is the name given to a nerve cell, and includes
the cell body with its nucleus, and all of its branches.
.pm fn-end
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:ch05# it was necessary to conclude that
there seemed to be no absolute dependence of
taste sensations upon the presence of taste buds.
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.h3
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
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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
// p085.png
.pn +1
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.
// p086.png
.pn +1
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
// p087.png
.pn +1
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
// p088.png
.pn +1
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.
.if h
.il fn=i088.jpg w=459px id=i088
.ca
Fig. 3.—Diagram showing some of the various courses which
have been advocated for the taste fibers in man. (Courtesy W.
B. Saunders Company.)
.ca-
.if-
.if t
.sp 2
[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.)]
.sp 2
.if-
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.:i088#), after Cushing, will show
// p089.png
.pn +1
the facts about the distribution of the gustatory
fibers.
.sp 2
.h3
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
// p090.png
.pn +1
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.[#] 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.
.pm fn-start // A
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.
.pm fn-end
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
// p091.png
.pn +1
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.
// p092.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER VII||Taste-Producing Substances
.sp 2
.h3
Adequate and Inadequate Stimuli
.ni
.sp 2
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
// p093.png
.pn +1
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.
.sp 2
.h3
Adequate Taste Stimuli
.pi
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,
// p094.png
.pn +1
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
// p095.png
.pn +1
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
// p096.png
.pn +1
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
// p097.png
.pn +1
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.
.sp 2
.h3
Inadequate Taste Stimuli
Our second question concerns the possibility of
other stimuli to taste, or of inadequate stimuli.
// p098.png
.pn +1
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
// p099.png
.pn +1
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
// p100.png
.pn +1
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
// p101.png
.pn +1
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,
// p102.png
.pn +1
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.
// p103.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER VIII||Function of the Taste Mechanism
.sp 2
.h3
Function of Tongue and Salivary Glands
.ni
.sp 2
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.
// p104.png
.pn +1
And it is just in these regions that we find that
the taste organs are located.
.pi
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
// p105.png
.pn +1
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
// p106.png
.pn +1
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.
// p107.png
.pn +1
.sp 2
.h3
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
// p108.png
.pn +1
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
// p109.png
.pn +1
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
// p110.png
.pn +1
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
// p111.png
.pn +1
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
// p112.png
.pn +1
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
// p113.png
.pn +1
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
// p114.png
.pn +1
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
// p115.png
.pn +1
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.
// p116.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER IX||The Development of Taste in the Individual
.sp 2
.h3
Development Before Birth
.ni
.sp 2
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.
.pi
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
// p117.png
.pn +1
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
// p118.png
.pn +1
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.
.sp 2
.h3
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
// p119.png
.pn +1
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.
// p120.png
.pn +1
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
// p121.png
.pn +1
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.
.sp 2
.h3
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
// p122.png
.pn +1
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.
.sp 2
.h3
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
// p123.png
.pn +1
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.
.sp 2
.h3
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
// p124.png
.pn +1
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
// p125.png
.pn +1
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
// p126.png
.pn +1
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.
.sp 2
.h3
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
// p127.png
.pn +1
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.
// p128.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER X||Evolution of Taste
.sp 2
.h3
Sensitivity of the Unicellular Organisms
.ni
.sp 2
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.
.pi
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
// p129.png
.pn +1
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.:ch06#) 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
// p130.png
.pn +1
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.
// p131.png
.pn +1
.sp 2
.h3
“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
// p132.png
.pn +1
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
// p133.png
.pn +1
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
// p134.png
.pn +1
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
// p135.png
.pn +1
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
// p136.png
.pn +1
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.
.sp 2
.h3
Chemical Sense in Fishes
In the fishes, again, the distinction between the
senses of smell and taste becomes more difficult,
// p137.png
.pn +1
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
// p138.png
.pn +1
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,
// p139.png
.pn +1
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.
.sp 2
.h3
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
// p140.png
.pn +1
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
// p141.png
.pn +1
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
// p142.png
.pn +1
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
// p143.png
.pn +1
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.
// p144.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER XI||Gustatory Imagination and Memory
.sp 2
.h3
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
// p145.png
.pn +1
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
// p146.png
.pn +1
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.
.sp 2
.h3
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
// p147.png
.pn +1
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:
// p148.png
.pn +1
.sp 2
.ta l:12 r:5
Vision | 57%
Hearing | 20%
Smell | 6%
Taste | 6%
Touch | 4%
Movement | 3%
Temperature | 2%
Organic | 1%
Emotional | 1%
.ta-
.sp 2
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
// p149.png
.pn +1
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.
.sp 2
.h3
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:
.ta l:10 c:10 c:10
| | Percentage of Occurrences |
| Sensory Mode |381
Dreams\
|300
Dreams
Vision | 84.5% | 67%
Hearing | 67.7% | 26%
Touch | 10.8% | 8%
Smell | 6.9% | 1%
Taste | 6.3% | 1%
.ta-
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
// p150.png
.pn +1
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.
// p151.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER XII||Unusual and Abnormal Taste Experiences
.sp 2
.h3
Gustatory Hallucinations and Auræ
.ni
.sp 2
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.
// p152.png
.pn +1
.pi
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.
.sp 2
.h3
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.
.sp 2
.h3
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
// p153.png
.pn +1
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.
.sp 2
.h3
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
// p154.png
.pn +1
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
// p155.png
.pn +1
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
// p156.png
.pn +1
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.
.sp 2
.h3
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
// p157.png
.pn +1
“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.
// p158.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER XIII||Food and Flavor
.sp 2
.h3
The Biological Rôle of Taste
.ni
.sp 2
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.
// p159.png
.pn +1
.pi
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
// p160.png
.pn +1
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?
.sp 2
.h3
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”
// p161.png
.pn +1
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:
.sp 2
.h3
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
// p162.png
.pn +1
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,
// p163.png
.pn +1
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
// p164.png
.pn +1
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
// p165.png
.pn +1
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.”
.sp 2
.h3
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
// p166.png
.pn +1
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
// p167.png
.pn +1
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.
// p168.png
.pn +1
.sp 2
.pb
.sp 4
.h2
CHAPTER XIV||The Æsthetic Value of Taste
.sp 2
.h3
The Higher and Lower Senses
.ni
.sp 2
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
// p169.png
.pn +1
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.
.pi
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
// p170.png
.pn +1
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.”
// p171.png
.pn +1
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,
// p172.png
.pn +1
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,
// p173.png
.pn +1
as well as those who busy themselves with
them, are quite likely to be esteemed “coarse”
and “nasty.”
.sp 2
.h3
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.
// p174.png
.pn +1
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.
.sp 2
.h3
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
// p175.png
.pn +1
// p176.png
.pn +1
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.
.sp 2
.if h
.dv class=font80
.ta |h:08 |h:15 |h:14 |c:14 |c:14|
=
Order of Æsthetic Value | Number of Discriminable Qualities|\
Sharpness of Discrimination |
Average Speed of Reaction|\
Average Duration of a Sensation, Degree of Inertia
_
Sight | About 40,000 | Difference of 1% |.189 sec. | About .030 sec.
| | | |
Hearing | About 15,000 | Difference of 33% |.146 sec. | About .002 sec.
| | | |
Smell | Nine classes, each with hundreds of qualities|\
Difference of 25% | Difficult to determine |Very long and difficult to determine
| | | |
Touch | Three or four classes with qualities no easily determined|\
Difference of 33% | .149 sec. | .001 to .002 sec.
| | | |
Taste | Four classes with number of qualities not determined |\
Doubtful | .300 sec. to 1.000 sec. | Very long and difficult to determine
| | | |
Kinæsthetic (Movement, Strain, etc.)|Four or five classes with number of degrees not determined|\
Difference of 5%| Difficult to determine | Undetermined
| | | |
Temperature | Two classes, degrees not determined |Variable and difficult to determine|\
.150 sec. to .180 sec | Difficult to determine
| | | |
Organic | About six classes | Unknown | Unknown | Unknown
_
.ta-
.dv-
.if-
.if t
.nf b
+——————+————————+———————+—————+——————+
| | | | | 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 | | | |
+——————+————————+———————+—————+——————+
.nf-
.if-
.sp 2
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
// p177.png
.pn +1
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
// p178.png
.pn +1
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
// p179.png
.pn +1
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?
// p180.png
.pn +1
.sp 2
.h3
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.
// p181.png
.pn +1
.sp 2
.h3
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
// p182.png
.pn +1
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.
.sp 2
.h3
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
// p183.png
.pn +1
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
// p184.png
.pn +1
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.
.sp 2
.h3
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
// p185.png
.pn +1
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.
.sp 2
.h3
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
// p186.png
.pn +1
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
// p187.png
.pn +1
basis of æsthetic value, ethical value, and genetic
development.
.sp 2
.h3
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
// p188.png
.pn +1
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
// p189.png
.pn +1
comment from Miss Calkins’ chapter on “Perception”
in her “Introduction to Psychology.”
As she there writes:
.pm letter-start
“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.”
.pm letter-end
// p190.png
.pn +1
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.
.sp 2
.h3
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
// p191.png
.pn +1
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,
// p192.png
.pn +1
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?
.sp 2
.h3
The Motive of Æsthetic Products
There is some further reason why the æsthetic
sense impressions are those which are genetically
// p193.png
.pn +1
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
// p194.png
.pn +1
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
// p195.png
.pn +1
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.
// p196.png
.pn +1
// p197.png
.pn +1
.sp 2
.pb
.sp 4
.h2
INDEX
.sp 2
.ix
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:uglytable#
Dreams, and taste, #124#, #149#, #186#
// p198.png
.pn +1
Drugs, effect of, #20#, #150#
Duration, of sensations, #175:uglytable#
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#
// p199.png
.pn +1
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:uglytable#
Quinine, taste of, #13#, #22#, #32#
Race differences, #126#
Rainey, #53#
Ramsay, #111#
Reactions, instinctive, #11#
time of, #56#, #175:uglytable#
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#
// p200.png
.pn +1
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#
.ix-
.sp 2
.pb
\_ // this gets the sp 4 recognized.
.sp 2
.dv class=tnbox // TN box start
.ul
.it Transcriber’s Notes:
.ul indent=1
.it Missing or obscured punctuation was silently corrected.
.it Typographical errors were silently corrected.
.it Inconsistent spelling and hyphenation were made consistent only when a\
predominant form was found in this book.
.if t
.it Text that was in italics is enclosed by underscores (_italics_).
.if-
.ul-
.ul-
.dv- // TN box end
\_ |