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.