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.
[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.