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.