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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
[Illustration: Publisher’s Logo]
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
Few people, comparatively, however intelligent and generally
thoughtful, have as yet stopped to consider the surpassing interest
and the unique importance of Our Senses. Living gateways as the sense
organs are between ourselves and our ever-changing surroundings, both
spiritual and material, they constitute the channels not only of our
_life-satisfaction_, but of all our immediate _knowledge_ as well. If,
then, in discussing them, biological imagination and breadth and depth
go hand in hand with technical knowledge of the highest grade, the
volumes comprised should be both human and scientific. And these
volumes are so, and will be. It is because of such possibilities that
a series like the present, authentic yet interesting and inexpensive,
must appeal to the intelligent man or woman of to-day. As
contributions to psychology and to education their value is certain to
be great, as indeed is indicated by the list of their authors, whom it
would be superfluous to praise or even to portray.
Small in number are the topics in all the wondrous range of the science
of living things that are more alluring for their very mystery and
romance than these same gateways by which we may go out into “our world”
and by which this same great world may come into us and, for the little
span of life, lend us a feeling of home-dwelling.
Within the past decade there has been a general popular awakening from
the former uninterested attitude toward these phenomena of the physical
and mental processes by which we keep in touch with the things outside
ourselves. A fair knowledge of the rudiments of biology, of physiology,
and of psychology now has become part of the curriculum of our schools
and colleges. And of these three sciences it is psychology which has
entered so deeply into our everyday life—business life as well as
personal—that at last no one can escape its influence. And no one wishes
to, for psychology in a sense has become the intellectual handmaiden of
all who think in terms of to-day, with to-day’s amazing development of
insight into the mortal meanings of our very selves, body always as well
as soul. Our scientific realization of our true continuity with all
things else goes on apace, and our personal relations to the boundless,
perhaps Infinite, Cosmos of consciousness, life, and energy seem ever
clearer. Thus, in a way, the sense organs give us personal anchorage in
a Sea which else sometimes, from its very immensity and stress, would
overwhelm us. Our range, although the broadest as yet vouchsafed to
life, is as it were but a mere line out into the complexity of the
Actual. The first step to the appreciation of this complexity and its
implications for the human mind is knowledge of the conditions of its
acquirement,—of the sense organs and of the perplexing brain behind
them.
Editorial duty or privilege fails to know much as yet of the detailed
contents of these several volumes. But the editor does know not a little
about the arrangers and expounders of the volumes’ contents, and he
knows that they are women and men of conspicuous sense—trustworthy in
every sense. The books are the best of their kind and are in a class by
themselves. They are the standard authority for ordinary use. These
volumes when disposed as a red-backed set on one’s library shelf will be
a set of books to be proud of. And the high school boys and girls and
their fathers evenings and on Sundays and their mothers at the club all
alike will think of them as highly valued friends, both wise and
agreeable, as pleasant to meet for an hour as the most welcome visitor
well could be. No higher “authority” exists than that which these
authors represent; and it would be hard to find those who could set
forth “authority” more gracefully. Each knows that literary _enjoyment_
usually goes hand in hand with that _wisdom_ which extended is the
director of Life itself.
Although the sense of taste is more strictly a “biological” sense than
any of the other simple senses of man—that is, more particularly
concerned with the underlying bodily life—it plays, nevertheless, a very
important part in our personal psychology. Many of us find in tasting
one of the fairly dependable satisfactions of our everyday living; and
Satisfaction, it seems upon long reflection, comes pretty close to being
the long-sought “highest good.” The wholly needless and harmful bodily
overweight of many of us attests how often this sense is made a
malignant fetish to lure us evilward. Eve tasted—and in that alluring
moment set an example too plain and too significant ever to be ignored.
The sense of taste, none the less, is a wholly respectable and dignified
mode of obtaining satisfaction.
And our respective “research magnificent” would _not_ be quite so
interesting, not so adventuresome, were our sense of taste, instead of a
clear sense experience tingling always with some kind of satisfaction,
were it, I say, only a subconscious instinct, part of the original
organic nature of man, working in the dark of consciousness. And for a
few of us, especially if we be chefs, or cooks, or tea-tasters, or
dyspeptics, or epicures, or gluttons, or taste-perverts, and the like,
taste is, perhaps, one of the most important of all mortal experiences
and of all scientific themes. And to the children how _much_ it is!
Professor Hollingworth and his Columbia colleague, Doctor Poffenberger,
have written a volume which seemingly would satisfy both the scientific
reader and the general readers who from curiosity seek its information.
The business man as well as his wife sitting beyond the living-room
table will both find the something they hoped to find; and the keen
school teacher and the all too infrequent schoolmaster will find part of
that material for the development of intensive sense-training now
obviously indispensable to the further evolution of our school system.
For even taste, least intellectual of our senses, can be intensively and
hence usefully trained and thus education be furthered.
The authors need no introduction to the educated million, but if they
did, this book would furnish one which the most exclusive hardly could
disdain. They are to be congratulated on the success with which they
have put much that is at once interesting and scientific up to the hour
into little space, with “war-time economy.” The authors have covered
their field well.
* * * * *
The editor takes this first opportunity to invite criticism of whatever
trend, and to ask for suggestions, whether from sense-gluttons or from
philosophers, for the better conduct and the furtherance of this series
and of that other series, on “The Life of the Child,” which he is
editing. As is true in a wholly different field of conquest, here, too,
lies safety in numbers, and where there are many men there are many
minds. As all authors at least will hasten to agree, not even an editor
knows all that might be known.
G.V.N.D.
CAMBRIDGE, MASSACHUSETTS,
_January, 1917_.
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PREFACE
The sense of taste is in numerous ways the most paradoxical of all the
senses. Although, as a source of sense impression, it can afford the
keenest immediate feelings of pleasure and delight, the books on
æsthetics and art have little or nothing to say about it. Skill in the
compounding of tastes and flavors, or discrimination in their relish,
brings the expert neither artistic recognition nor social eminence.
Taste, it is constantly asserted, is one of the “lower senses,” and
neither in the enjoyment of it nor the ministration to it is there to be
acquired the merit and general esteem that readily distinguish an art
from a service.
Nevertheless we commonly use the word “taste” for the expression of just
those qualities of fine discrimination and delicate perception which are
most conspicuously the marks of æsthetic appreciation. In our choice of
figures of speech we reserve “vision” for the impersonal and remote
intuition of the seer and the philosopher. “Touch” we use to express
such intimate and personal impressions as sympathy and pity. “Sound”
seems best to indicate, through “noise” or “tone,” either the
self-seeking clamor of aggression or the mere passive possession of a
certain richness of quality. “Odor,” in its most common figurative use,
suggests the reprehensible and undesirable motive. “Warmth” and “chill”
bespeak at once the depth of emotion or affection. But the special
fineness of soul which shows itself in the active and judicious choice
of the appropriate and the harmonious, the subtly fitting and the
delicately adapted, seems best expressed by the name of one of the
“lowest” and most “vulgar” of senses,—“taste.” Whether the judgment be
exercised in the choice of color harmony or musical composition, costume
or personal ornament, architecture, monument, design or arrangement,
poetry or passing jest, rug, menu, pastime or associates, it is the
sense of taste which furnishes the apt name for the critical capacity.
Not only is it in the usages of language that taste is a paradoxical
sense; it is at the same time one of the most ancient of the special
senses and also one about which exact knowledge is most difficult to
acquire. It seems to afford a multitude of varying and distinctive
_nuances_ of sensation, yet it can boast but a meager equipment of four
fundamental sense qualities. It is a primitive and well-established
sense in the evolution of man, and individuals might therefore be
expected to resemble each other closely in their experience of it; yet
the most trite of proverbs insists that “there is no accounting for
tastes.” Indeed, in some languages it is even impossible to find
distinctive names for such common taste experiences as bitter or even
salt and sour. A survey of the phenomena and laws of the sense of taste
reveals, in fact, no end of curious and interesting situations.
Of particular interest are the recent demonstrations of the great
importance of taste for the general well-being of the organism. With the
development of civilized modes of living men cease to rely implicitly or
entirely on the sense of taste in their discrimination between wholesome
and deleterious foods. They substitute for taste the evidence of the
commercial trade-mark, the label, and the pure-food guarantee. It might
have been supposed that under such circumstances the sense of taste
would deteriorate through loss of function. But recent studies show that
sensations of taste do far more than serve as clues to the acceptance or
rejection of food. Such sensations appear, in fact, to be the initial
stimulus to the whole series of digestive and assimilative processes on
which the well-being of the organism depends. In much the same way the
dulling or perversion of the taste sensations is often seen to
constitute an early warning of grave disorder in the system as a whole,
and their restoration to presage the return to normal health.
Developing as one of the earliest forms of sensitiveness, intimately
associated with the vital processes of life and growth, affording
manifold richness of pleasure and aversion, full of paradoxical
surprises and puzzling problems, and figuratively expressing one of the
rarest of human qualities, “the sense of taste” constitutes one of man’s
most interesting contacts with the outer world.
In the chapters which follow an attempt is made to portray this contact
in a manner which is both clear and concrete, yet scientifically
accurate and technically complete. There are first considered the actual
experiences which the sense of taste affords, their character, their
analysis into the elementary qualities, and the classification,
relations, and manner of combination of these qualities. A consideration
of the delicacy of the taste sense, the precision of taste
discrimination, and their methods of measurement, is followed by a
discussion of the time relations of taste sensations, and a description
of various special characteristics and phenomena of normal and abnormal
tastes.
At this point there is presented a detailed description and illustration
of the mechanism and function of the organ of taste, its gross structure
and anatomy, its accessory apparatus, its more minute nervous basis and
composition, and its evolution in the individual and in the lower animal
forms. Chapters are given to the nature of the external stimulus which
provokes taste sensations, to disorders of the taste sense, to the
differences between individuals, and to the function of sensations of
taste in the higher mental processes of imagination, association,
memory, and emotion. Finally, an account of the function of taste in the
life of the organism is followed by a consideration of the place of the
sense of taste in æsthetics and art, and in the complex interplay of
human thought and social communication.
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CONTENTS
CHAPTER PAGE
EDITORIAL INTRODUCTION vii
PREFACE xiii
I THE QUALITIES OF TASTE 1
The Taste Manifold—The Classification
of Tastes—Taste Blends and Fusions—The
Poverty of Taste—Psychological
Analysis of the Taste
Qualities—Distribution of the Taste
Qualities—The Vocabulary of Taste.
II THE ORGANIZATION OF THE TASTES 27
System and Organization in Other
Senses—Taste Mixtures and
Compounds—Compensation, Antagonism,
and Neutralization—Contrast
Phenomena—After Images of Taste—The
Schema of Taste Relations.
III THE SENSITIVENESS OF TASTE 43
Various Measures of Sensitiveness—The
Threshold of Taste Sensation—Relative
Sensitivity of Taste and Smell—The
Discrimination of Tastes—Adaptation
and Fatigue—Acquired Tastes—The Early
Development of Taste.
IV TIME RELATIONS OF TASTE QUALITIES 55
The Inertia of the Taste
Organs—Reaction Time to Taste
Stimuli—Determinants of Reaction Time
to Taste.
V THE SENSE ORGAN OF TASTE 60
Comparison with other Sense Organs—The
Salivary Glands and Their Activity—The
Tongue: Its Muscles and Covering
Membranes—Classification of
Papillæ—The Determination of the Taste
Areas.
VI SENSORY ELEMENTS OF THE TASTE MECHANISM 78
Taste Buds and Their General
Characteristics—Supporting Cells,
Gustatory Cells, and Nerve
Filaments—Relations Among the
Structures within the Taste Bud—The
Sensory Nerves of Taste—The Cerebral
Taste Centers.
VII TASTE-PRODUCING SUBSTANCES 92
Adequate and Inadequate
Stimuli—Adequate Taste
Stimuli—Inadequate Taste Stimuli.
VIII THE FUNCTION OF THE TASTE MECHANISM 103
The Function of Tongue and Salivary
Glands—The Function of the Taste Buds.
IX THE DEVELOPMENT OF TASTE IN THE 116
INDIVIDUAL
Development Before Birth—Development
of Taste in Infancy and
Childhood—Taste in the
Adult—Structural and Functional
Differences Among
Individuals—Individual Differences Due
to Pathological Changes—Racial
Differences in the Structure and
Function of the Taste Organs.
X EVOLUTION OF TASTE 128
Sensitivity of the Unicellular
Organisms—“The Chemical
Sense”—Chemical Sense in
Fishes—Land-Dwelling Animals.
XI GUSTATORY IMAGINATION AND MEMORY 144
The Nature and Frequency of Mental
Images—Mental Images of Taste—Taste in
Dreams and in Hallucinations.
XII UNUSUAL AND ABNORMAL TASTE EXPERIENCES 151
Gustatory Hallucinations and
Auræ—Partial and Complete
Ageusia—Taste Hallucinations of the
Insane—Synæsthesias of
Taste—Perversions of Taste.
XIII FOOD AND FLAVOR 158
The Biological Rôle of Taste—Taste and
Digestion—Experimental Evidences—The
Function of Taste in the Organic
Economy.
XIV THE ÆSTHETIC VALUE OF TASTE 168
The Higher and Lower Senses—Bounty of
Nature and Ecclesiastical
Censorship—The Psychophysical
Attributes—The Tendency to
Adaptation—Spatial Attributes of Taste
Qualities—Immediate Affective Value of
Taste—Development in the Individual
and the Race—The Imaginative Value of
Taste—The Non-Social Character of the
Lower Senses—The Unsystematic
Relations of Taste Qualities—The
Motive of Æsthetic Products.
INDEX 197
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ILLUSTRATIONS
Diagram showing relations between the 40
taste qualities
Sketch of the tongue 69
Diagram showing some of the various 88
courses which have been advocated for
the taste fibers in man
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THE SENSE OF TASTE
CHAPTER I
THE QUALITIES OF TASTE
_The Taste Manifold_
THE casual observer would probably feel that any attempt to enumerate
and arrange in a logical scheme the infinitude of tastes and flavors
would be an impossible task. To him it might seem that nearly everything
in the world possessed its own peculiar taste. Such an observer would
also be likely to think it impossible and thankless to attempt to reduce
to their necessary limits the various kinds of substance of which this
infinitude of things is made up. But the chemist would readily be able
to show him that the infinitude of substances consisted, as a matter of
fact, only of various forms and combinations of less than one hundred
“elements,” and that from these elements one could produce, by
appropriate selection and apportionment, any one of the infinitude of
substances.
Is it then possible, in the field of our sensations, to reduce to
elemental categories or units the manifold[1] of concrete sense
experience? In the case of visual sensations almost everybody knows that
there are certain so-called “primary” colors, from which can be produced
the whole range of color experiences known to man. Blue and yellow, red
and green, these are the primary colors, and if to these, in their
varying intensities, be added gray, with its range of brightnesses, we
have the elementary components of all our visual experience. Such a
distinctive color as that of fire clay, for example, may thus be said to
contain, in specified degree and proportion, red, yellow, and gray,
while the familiar color of a wild flower may contain, in specified
relations, red, blue, and gray.
Footnote 1:
By a “manifold” is meant a great variety of objects or experiences
organized into one system or constituting one field.
In a strict psychological sense, it remains true that each color
experience is relatively unique and distinct. But it can readily be
shown that these psychological fusions and compounds are elaborations of
more unitary experiences which have as their basis distinct mechanisms
in the nervous system and sense organs. For example, the sensation of
“heat” is a readily recognizable and identifiable experience, yet the
physiologist tells us that there is no separate sensory apparatus for
this impression. Cold and warmth, we are told, depend on the stimulation
of specific nerve endings. When these two types of endings, in the same
general region of the skin, are simultaneously stimulated, as the result
of the application of a stimulus with very high temperature, there
arises that new experience of “hot,” which is in this sense a
combination of warmth and cold.
Is it similarly possible to reduce to elementary units the rich manifold
of taste and flavor? If this can be done, in what way must such an
analysis proceed? What principles of classification are revealed, and
what and how numerous are the elementary taste qualities? The various
attempts that have been made to analyze the taste manifold are as
interesting as their results are instructive.
_The Classification of Tastes_
One method of classifying sense qualities that has often been advocated
uses as its basis the varieties of objects, agencies, or stimuli[2] by
the application of which the sense qualities are produced or aroused.
Thus the whole field of sense experience might be divided into thermal,
electrical, mechanical, photic (produced by light), etc. But such
sensations as are aroused by electrical stimuli, for example, may be
auditory, visual, cutaneous, gustatory (having to do with taste), etc.,
while these same varieties of sensory experiences may be aroused in some
cases by mechanical stimulation. Hence the classification of stimuli
does not yield an adequate analysis of modes of sensation. In the field
of taste this method, although it has been seriously attempted, is
equally futile. Thus various writers have attempted to group taste
sensations according to the species of plants and animals whose tissues
possessed sapid (taste-producing) qualities. It is obvious that this
method is unsatisfactory, since it is by no means true that all
specimens of a given vegetable taste alike. Even different parts of the
same plant have widely different tastes, and indeed the taste of a given
part varies widely with time and circumstances.
Footnote 2:
By a “stimulus,” in this connection, is meant any object, force, or
agent that acts upon a sense organ.
Even Chevreul, a famous early student of the sense of taste, adopted a
chemical classification, on the basis of the composition of the
substance tasted. Here again it is true that substances chemically very
dissimilar may possess tastes which are strikingly alike. Thus acetate
of lead, chloroform, and cane sugar, which, chemically considered, are
very dissimilar, may easily be mistaken for each other if their taste
alone is relied on; while starch, which is chemically closely related to
sugar, has no taste. It is also true that such different tastes as sweet
and bitter may characterize substances which are chemically very closely
related.
It is, however, true that certain broad lines of chemical classification
may be drawn. Thus those substances belonging to the colloid[3] group
are tasteless, the crystalloids all being sapid. When substances are
arranged according to the “periodic law” of chemistry, the elements
present in sweet-tasting substances are in general neither extremely
positive nor extremely negative. While it is the general rule that
soluble alkaloids are bitter, acids sour, sugars sweet, and salts salty,
there are many curious exceptions in every case. “It is true that we get
the taste of salt only from chemical salt; but there are chemical salts
that taste sweet, others that taste bitter, others again that have no
taste at all.” Similarly, while it is true that sour tastes belong to
acids, it is by no means true that all acids taste sour. Moreover, sugar
of lead, which is a salt, tastes sweet; while sulphate of magnesia and
other salts taste bitter.
Footnote 3:
Resembling jelly or glue, uncrystalline in character.
Indeed, it is true that there are substances which have more than one
taste, the taste varying with the region of the tongue at which the
substance is applied. Thus saccharine, sulphate of magnesia, and acetate
of potassium are said to have sweet or acid taste if applied to the side
or tip of the tongue; whereas they are bitter if applied to the
posterior part. There are various other substances which show similar
changes in taste according to the point of their application. However
such facts may be explained, it is clear that the classification of
taste along chemical lines is not only beset with difficulties, but that
even in attempting such classification we resort to the use of a more
immediate classification, indicated by such words as sweet, sour, etc.
This resort to an immediately descriptive classification suggests that
the various taste experiences, regardless of the stimulus provoking
them, have certain similarities as direct experiences. This further
suggests that a strict psychological classification, based on the
attributes of tastes themselves, should be found through analysis. In
the case of sensations in general, such a type of classification is the
one that seems most satisfactory. Certain sense experiences, such as
red, yellow, orange, seem, as a matter of immediate experience, to
belong together and to be essentially different from such experiences as
warmth, tickle, noise, dizziness, etc. Furthermore, it is found possible
to pass by gradual steps of transition from red to yellow, through an
intervening orange, while there exists no such intermediate region
between red and tickle. As a matter of immediate experience, then, and
regardless of the nature of the stimulus, or, so far as we may be aware,
of the part of the body stimulated, certain sense experiences seem to
belong together, to constitute a certain _mode_ of sensation, such as
pressure, sound, etc.
Is it now possible to apply a similar test to the various _qualities_
which comprise the _mode_ or _sense_ of taste, and thus arrive at an
adequate classification and analysis of these qualities? The earliest
attempts to analyze the tastes by this psychological method were often
amusingly miscalculated. Thus Chatin, in 1880, presented a scheme in
which the total manifold of taste was first divided into agreeable
tastes and disagreeable tastes. The agreeable tastes were typified by
those we call sweet, and the disagreeable by those we call bitter. It
was, of course, at once necessary to indicate certain intermediate
conditions in this scheme for a variety of tastes which were neither
clearly agreeable nor markedly unpleasant. Moreover, it is a matter of
common experience that a taste which is agreeable to one person (such as
tobacco, olives, mustard) may be decidedly obnoxious to another person,
or, indeed, even to the same person on a different occasion; so that
such a classification cannot be said to represent in any fundamental way
an analysis of tastes.
There have been a great variety of classifications proposed on this
direct descriptive basis, and a comparison of the various schemes at
once suggests that the task is by no means as simple as it might seem.
The number of elementary tastes ranges widely, some investigators
enumerating five or six times as many fundamental taste qualities as
others have recognized.
Haller enumerated twelve different qualities—stale, sweet, bitter, sour,
sharp, tart, spicy, salt, urinous, putrid, spirituous, nauseating. It is
evident that this classification represents only a transition step
toward a psychological analysis and that it is by no means free from the
suggestion of provoking substances (spirituous, putrid) and the
suggestion of effects produced (nauseating).
Linnæus recognized somewhat fewer categories,—giving the following ten
as fundamental,—sweet, spicy, oily, mucous, salt, styptic,[4] bitter,
sour, aqueous, and dry.
Footnote 4:
Styptic,—causing contraction of tissues.
Other authors have been content with indicating eight elementary tastes.
Both Bain and Wundt have proposed a sixfold classification, as
follows,—sweet, bitter, saline, alkaline, acid, and astringent or
metallic. Most modern authorities reduce the number of elementary tastes
to four,—sweet, salt, sour, bitter,—while at least three investigators
have advocated a simple twofold classification, into sweet and bitter.
_Taste Blends and Fusions_
These divergent accounts of the elementary taste qualities are in large
measure to be explained by the exceeding complexity of those experiences
which we in everyday life refer to as “tastes.” It was long ago shown
that a classification of the various senses on the basis of the gross
“sense organs” or parts of the body involved is as inadequate as one
based on the nature of the stimulating agent. The eye as a gross sense
organ yields experiences of pressure, pain, temperature, and strain, as
well as experiences of color and brightness. But these varied sensations
we recognize as belonging, as experiences, to quite distinct modes. Even
more complex are the varied sense experiences which we may receive
through stimulation of the tongue and the surrounding tissues. For the
tongue as an organ yields not only sensations of pure taste quality,
whatever these may be, but it also gives rise to experiences of pressure
with the varying characteristics of smooth, rough, moist, dry, contact,
tickle, etc.; to experiences of pain, with the ranging characteristics
and intensities, such as sting, smart, prick, burn; to experiences of
temperature, such as cold, warmth, heat; and to a vast complex of
kinæsthetic or muscular experiences of contraction, torsion, strain,
expansion.
In common experience these qualities of pressure, pain, temperature, and
kinæsthesis are scarcely discriminated from the purely gustatory or
taste qualities themselves. Thus we speak of “oily,” “fatty,” and
“greasy” tastes, in which the “smoothness” is certainly identical with
that felt by the fingers and other parts of the skin. Similarly the
pungent, astringent, puckering, biting “tastes” may come from substances
which have no taste at all in a strict sense, but which produce definite
smarting or stinging sensations when applied to the surface of the skin
or to exposed nerve endings (pepper, camphor). The puckering quality can
be shown by the characteristic muscular reaction to be largely
kinæsthetic and tactual in its origin. The difference in “taste” between
cold ice cream and the same substance when melted indicates how much of
the flavor is due to touch sensations and sensations of temperature. One
observer, indeed, reports the experience of four different qualities of
sensation from the stimulation of a single papilla,—a touch, a
temperature, a taste, and a pain sensation.
Further, many substances, in addition to these locally aroused
experiences of touch, temperature, pain, and movement, set up strong
organic reactions in more or less remote regions as well as strong
affective reactions: such as choking, nausea, and vomiting, on the one
hand, and extreme unpleasantness, disgust, distress, strain, and shock,
on the other. In many cases these immediate reactions seem to be reflex
or instinctive in their origin, and in other cases they seem to be
conditioned reactions, based on past experiences and associations. Thus
in one case the “taste” of ice cream, which was once agreeable enough,
has come to be immediately nauseating in character.
In spite of all these facts many of the classifications of taste
qualities have included the “oily,” the “nauseous,” the “astringent,”
etc., as primary taste experiences. Even if the complications we have
thus far alluded to were the only ones concerned, it would be clear
enough that the “tastes” and “flavors” of everyday conversation
represent very complex fusions and compounds, and that an analysis of
the true taste qualities, if such there be, must take these factors into
account in some very careful experimental way.
But we have left until this point a single complicating factor which in
itself is sufficiently serious to call for very careful technical
procedure in the examination of the sense of taste. This is the fact
that a very great number of our so-called tastes are not tastes at all,
but really odors. The sense organ of smell is so situated that it may be
stimulated not only in the ordinary way, through particles borne into
the nostrils by currents of air from the outside, but also by particles
and vapors which pass up, from the mouth cavity, behind the soft palate,
by way of passages called the “posterior nares.”
In this way it happens that tasteless substances, with definite odor,
are mistakenly supposed to have taste. In 1824 Chevreul reported a very
simple experiment with which his name has since been universally
associated. He pointed out that it is impossible to separate the action
of a substance on the touch corpuscles of the tongue from its action on
the taste buds themselves. He observed, however, that by a very simple
expedient it is possible to eliminate to some degree the factor of odor.
His classical experiment consisted in excluding the sense of smell in
large part by pressing the nostrils with the fingers while the substance
to be examined was presented to the tongue. In this manner he observed
that a piece of camphor gum which had seemed to have a very distinctive
taste had in reality no taste at all. When the nostrils were closed all
that could be observed as the result of placing camphor on the tongue
was a peculiar pricking sensation of touch, similar to that produced by
various other substances. The sensation produced by the camphor was thus
not a taste at all, but a fusion of odor and touch.
If, under the simple conditions of Chevreul’s experiment, the various
substances be reduced to a state of like consistency, so that they
cannot be recognized by the tactile sense, observers are usually much
amazed to discover that through taste alone it is impossible to
distinguish between quinine and coffee or between apple and onion. Many
familiar experiences of daily life testify to the large contribution
which the sense of smell makes to the supposed taste. How “tasteless”
are our fruits, wines, cigars, and vegetables when one has a cold in the
head, and the free passage of odorous particles to the organ of smell is
obstructed! How often has the nasty taste of medicine been softened by
Chevreul’s simple technic of “holding the nose”! There are some cases in
which the reverse of this situation occurs and volatile substances,
entering the mouth through the nostrils, stimulate the taste buds in the
upper and back part of the mouth. In such relatively rare cases the real
taste is mistakenly interpreted as an odor. In this way chloroform seems
to have the characteristic odor which is in all probability a sweet
taste due to stimulation of the taste buds by the chloroform vapor.
Why should it be the rule that, since the taste and smell qualities are
to be confused, smell should so commonly sacrifice its claim, so that
odors are called tastes rather than vice versa? No doubt this is true
largely because of the customary presence of sensations of pressure,
temperature, movement, and resistance which are localized in the mouth
and in the organ of taste. These accompanying sensations suggest that
the taste organs are active in determining the result, even when no true
taste qualities are present. It is common for sensations to be displaced
in some such way as this, just as the blind man, who is really getting
sensations from stimuli in the palm of his hand, seems to be getting
them at the end of his walking stick; or just as a faint sound may seem
to come from any source to which we direct our attention. Similarly, the
whole complex of touch, taste, and odor experienced as the result of
“sniffing” at a particular substance are quite likely to be credited
entirely to the sense of smell.
_The Poverty of Taste_
Here, then, is a most interesting situation, which has been described by
the use of two apt phrases: “the poverty of taste” and “the
self-sacrificing character of smell.” Our analysis has tended constantly
to rob the sense of taste of the richness which we ordinarily credit to
it. In fact, modern authorities agree that there are only four qualities
which can be truthfully classed as tastes, namely, sweet, salt, sour,
and bitter. What we took to be the taste manifold is really a meager
equipment of four qualities, with such variations of intensity and
combination as these may possess. Both the richness and the manifoldness
come from qualities of other senses, parading under the guise of taste.
Smell especially is prone to sacrifice its claim in favor of its
neighbor, and it is common indeed for us even to use taste names in
describing odors; we speak of “sweet odors” and “sour smells,” although
sweet and sour are primarily taste qualities. Smell, then, not only
entirely yields many of its qualities to the various “taste blends,” but
allows some of its own sensations to pass under taste names.
Patrick has reported extended observations in which he studied the taste
experiences of an anosmic,—a person who had lost the sense of smell. In
some of his experiments this woman, with two other women as control
subjects, after having been blindfolded, attempted to identify various
substances taken into the mouth. The general principles on which the
experiments were based are stated as follows: “In theory those
substances not recognized by any of the observers depend for their
recognition upon sensations of sight; those recognized by the normal
observers but not by the anosmic depend upon sensations of smell for
their recognition; while those recognized by all observers depend upon
either taste, touch, or muscle sensations.” It was further suggested
that those substances recognized by the anosmic but not by the normal
subjects would seem to depend in the main upon touch or muscle
sensations.
These experiments disclosed many curious and unexpected facts. Breads
and meats, butter, cream, olive oil, and various fruits and vegetables
could not be easily identified when only sight was excluded. One of the
women, a housekeeper of long experience, could not recognize raw turnip,
raw potato, boiled pumpkin, cranberry sauce, or fresh pear when she was
blindfolded.
Chicken, turkey, and quail were found to differ surprisingly little in
actual taste, especially if their characteristic texture, smoothness,
and other tactual qualities were eliminated or disguised. The various
values placed upon different meats, breads, etc., in the general esteem
would seem to depend in great measure on associated ideas and emotions,
rather than on their actual qualities for taste.
Especially interesting is the list of substances which were recognized
and correctly named by both of the normal women in these experiments,
but which the anosmic was unable to identify. Patrick enumerates
twenty-seven such common substances. Among them, by way of example, were
vanilla extract, pineapple syrup, banana, grape, quince, strawberry,
tea, chocolate, sour milk, kerosene, claret, rhubarb, onion, eggs, and
boiled turnips. The results suggest that these substances, although they
seem to have very characteristic tastes, are actually differentiated and
recognized on the basis of their olfactory rather than their gustatory
or tactual qualities.
One justification of this olfactory sacrifice is suggested by the fact
that biologically one of the most important functions performed by smell
is that of aiding in the discrimination of food. Through smell the
animals perceive at a distance a substance which may offer itself as
possible food. Biologically, the immediate guide to the acceptance or
refusal of food is the sense of taste. In so far as smell is in part a
subordinate servant in this matter, and hence becomes easily associated
with such reactions as “eating” or “not eating,” no injury is produced
through the occasional confusion of the two modes.
We have thus reduced the rich manifold of taste to the qualities of
sweet, salt, sour, and bitter,—four meager qualities as compared with
the numerous unanalyzable qualities of various of the other sensory
modes. We have now to show by what logic, through what technic, and on
the basis of what evidence, we are compelled to grant to taste four
qualities rather than two or twelve, and why the final grant consists of
these particular four rather than others.
_Psychological Analysis of the Taste Qualities_
As Chatin long ago observed, “The three senses,—taste, touch, and
smell,—are so intimately combined that they seem to refuse to yield
themselves to minute analysis.” These associations seem to be even
stronger than those between the various taste qualities, of which Ladd
and Woodworth have remarked, “On the whole it appears as if the four
tastes were rather isolated from each other, each representing almost an
independent sense. There is much blending, to be sure, but the amount is
apparently no greater between one taste and another than between tastes
and odors.”
We may now fairly ask how these four qualities may be made to reveal
their elementary and independent character, once we have eliminated the
complicating factors introduced by the intrusion of qualities from other
senses.
The first appeal is to common observation and experience, according to
which the four taste qualities,—sweet, sour, salt, and bitter,—stand out
as conspicuous classes within which may be placed a great variety of
“taste blends.” Thus many substances, while having more or less
distinctive flavors, resemble each other in that unanalyzable quality
which we call sweetness. The only question here is whether or not we
should also include qualities other than these four as ultimate and
irreducible. If we refer back to the lists of tastes proposed, we find
that many of them are such as can be shown to be analyzable into one or
more of these four qualities, plus the intrusion of tactile, thermal,
kinæsthetic, and olfactory qualities. Such tastes as nauseating,
aqueous, astringent, styptic, putrid, etc., are easily ruled out on this
score alone. Introspectively, by simple experimental variation, or by
casual observation, the complex character of many of these tastes is
easily revealed, and when the non-gustatory components are eliminated
the residue falls readily under one or other of our four qualities.
These reductions are borne out by definite experiment. The tactile
(touch), thermal (temperature), and kinæsthetic (movement) factors are
kept constant and reduced to a minimum by applying minute amounts of
various solutions to single papillæ or very small regions of the tongue.
Smell may be, under these conditions, in great measure eliminated by
closing the nostrils with cotton or wax, and by letting the tongue be
somewhat advanced beyond its usual position. When these conditions are
observed, it is found that the main sense qualities experienced are
those of salt, sour, sweet, and bitter, along with such touch sensations
as may be unavoidable. Temperature may be eliminated by having the
solutions maintained at the temperature to which the tongue is already
adapted.
The evidence on this point is not absolutely consistent. Some observers,
for example, feel impelled to add metallic and alkaline to the group,
making six elementary qualities instead of four. Other observers,—most,
in fact,—are persuaded that the metallic and alkaline qualities
represent mixtures of the salt, sour, sweet, and bitter, along with
unavoidable sensations of touch and smell. Thus, by a suitable mixture
of strong solutions of salt and sweet substances, the alkaline taste may
be very well produced. “It has been suggested that the metallic taste is
due to the simultaneous development of salt and sour tastes. The failure
to produce exact alkaline and metallic tastes synthetically is in part
due to the difficulty of imitating the tactual and other sensations with
which they are bound up.” Still other observers are convinced by careful
elimination of smell sensation that the unique character of the alkaline
and metallic qualities is really a question of odor.
By the application of specific drugs to the organ of taste further
indications are secured that these four qualities, unanalyzable to
introspection, also function in relative independence. Thus, the juice
of gymnema leaves temporarily destroys the qualities of sweet and
bitter, while sensitiveness to sour and salt remains unimpaired. “The
true acid or sour taste may be separated from the astringent effect
which accompanies it by painting the tongue several times with a five to
ten per cent solution of cocaine. Cocaine first abolishes the sour
taste, and after several minutes begins to abolish the astringent action
of the acid solution. Later, the sour sensation begins to return, while
the astringent effect is still in abeyance, so that the application of
an acid solution at a certain stage during recovery enables the true
taste character of sour to be differentiated.” It is also reported that
when gymnemic acid and cocaine are applied to the tongue, the one
abolishes the sweet and the other the bitter, thus leaving the two other
tastes relatively unimpaired. Certain mixtures seem to paralyze both
sweet and bitter, but the former sooner than the latter.
_Distribution of the Taste Qualities_
To these four elementary tastes we are not equally sensitive on all
parts of the sense organ. Roughly speaking, sweet is best tasted at the
tip of the tongue, and many forms of candy are prepared so as to allow
as much as possible the employment of this part of the taste organ.
Bitter, on the other hand, is best tasted at the back or root of the
tongue, which explains why many substances do not taste bitter until we
have swallowed them. The edges of the tongue are most sensitive to sour,
while in adults the central area does not commonly yield taste qualities
at all. In children, however, the taste buds extend not only over the
whole surface of the tongue, but are also found in the walls of the
cheek, the palate, and even on the larynx and epiglottis. Titchener has
suggested that these facts may explain “the childish tendency to take
big mouthfuls.”
Attempts have been made to determine whether these elementary taste
qualities depend on separate taste buds or papillæ. Experiments show it
to be true that some points respond only to sweet, sour, etc. But there
are others which yield two or three or even all four qualities, while
some yield no taste at all. In one such experiment thirty-nine papillæ,
in a certain region, were separately stimulated by acid, sugar, salt,
and quinine. Of these thirty-nine, thirty-one responded to salt, and the
same number to sweet, twenty-nine to sour, twenty-one to bitter. Four
yielded no taste at all, one responded only to bitter, and one to sweet.
In another case of one hundred and twenty-five papillæ examined by
solutions of sugar, quinine, and tartaric acid, sixty gave sensations of
all three qualities (sweet, sour, bitter), twelve gave both sweet and
sour, twelve sour only, seven bitter and sour, four bitter and sweet,
and three sweet only. None of them seemed to give a bitter quality alone
and this seems to be the general rule.
It is of course difficult in these experiments to restrict the
application of the stimulus to single taste buds or even to single
papillæ. But these experiments, along with the effects of drugs which we
have already described, suggest that the taste buds are not all alike in
function, even though they seem quite similar so far as appearance and
structure are concerned.
_The Vocabulary of Taste_
Several investigators have been interested in the study of the taste
names found in different languages and communities. It has been
suggested that such a study might throw light on the order of
development of the various taste qualities.
Kiesow found that both children and adults quite commonly confused
bitter with salt and sour. Myers found, in studying the taste names of
primitive people in the region of the Torres Straits, that they had no
word for bitter. In some primitive languages the same word is used for
sweet and salt. When there is a word for salt it is usually some
derivative of the word for sea water. Salt and sour are also often
confused. In Polynesia, indeed, a single word is used in describing
salt, sour, and bitter tastes. This is analogous to the fact that in
primitive languages it is often found that the same word is used to
indicate blue and black.
Attempts to argue from these facts of vocabulary to facts of
sensitiveness and order of development are, of course, open to many
sources of error. As Myers points out, “The differences between sour and
bitter are considered less striking than their common unpalatability.”
It has often been pointed out that in our own language sweet is probably
the only taste word that had from its very origin a gustatory meaning.
In some languages even the word for sweet means literally “tasting
good.”
Vocabularies do not develop in order that structural and functional
facts may be recorded for the information of forthcoming scientists.
Words arise in response to the demands of practical life. It is
practically more important that some substances “taste good,” and others
“taste bad,” than that there are just four elementary taste qualities.
Hence for certain primitive circumstances two taste words are all that
are needed in ordinary conversation. It by no means follows from this
that the salt, sour, and bitter, which all fall in the “bad taste”
category, are not discriminable from one another by the taste organs of
the savage. It would be just as cogent to insist that, since we have
only one word for the taste of various sour things, all of these various
tastes must be indistinguishable to us.
Nor is the argument safe that those sense qualities for which specific
names exist must be more ancient than those qualities for which names
are borrowed. Many of our color names are not primarily color names at
all,—as violet, rose, olive, turquoise, lemon, straw, orange, and,
perhaps, pink and green. Red, blue, and yellow seem to be more
essentially color names. Yet, it is difficult to suppose that an
organism sensitive to red and yellow should not also be sensitive to
orange, which may be produced by a mixture of red and yellow light.
In the case of the odors, which we have every reason to believe are
extremely ancient sense qualities, we have in our own language almost no
exclusively olfactory names. Smells are designated by the objects with
which they are associated,—as lilac, lavender, musk; or names are
borrowed from other sensory modes, as sweet, sour, heavy; or still more
descriptive and perceptual names are used, such as fresh, flat, rancid,
foul, nauseating. Interesting as the vagaries of vocabulary may be, they
yield very little information concerning the primitiveness,
elementariness, sensitiveness, or distribution of the various taste
qualities.
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