The Sense of Taste

CHAPTER I. The Qualities of Taste

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 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 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 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.

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