f the four tastes; and the
bitter taste is aroused principally from {202} the back of the tongue,
the sweet from the tip, the sour from the sides, the salty from both
tip and sides.

The stimulus to the sense of taste is something of a chemical nature.
The tasteable substances must be in solution in order to penetrate the
pits and get to the sensitive tips of the taste cells. If the upper
surface of the tongue is first dried, a dry lump of sugar or salt laid
on it gives no sensation of taste until a little saliva has
accumulated and dissolved some of the substance.

Exactly what is the chemical agent that produces a given taste
sensation is a problem of some difficulty. Many different substances
give the sensation of bitter, and the question is, what there is
common to all these substances. The sweet taste is aroused not only by
sugar, but by glycerine, saccharine, and even "sugar of lead" (lead
acetate). The sour taste is aroused by most acids, but not by all, and
also by some substances that are not chemically acids. Thus the
chemistry of taste stimuli involves something not as yet understood.

Though there is this uncertainty regarding the stimulus, on the whole
the sense of taste affords a fine example of success achieved by
experimental methods in the analysis of complex sensations. At the
same time it affords a fine example of the fusion of different
sensations into characteristic _blends_. The numerous "tastes" of
every-day life, though found on analysis to be compounded of taste,
smell, touch, pain, temperature and muscle sensations, have the effect
of units. The taste of lemonade, for example, compounded of sweet,
sour, cold and lemon odor, has the effect of a single characteristic
sensation. It can be analyzed, but it ordinarily appears as a unit.
This is true generally of blends; indeed, what we mean by blending is
that, while the component sensations are still present and can be
found by careful attention, they are not simply present together {203}
but are compounded into a characteristic total. Each elementary
sensation entering into the blend gives up some of its own quality,
as, in the case of lemonade, neither the sweet nor the sour is quite
so distinct and obtrusive as either would be if present alone. The
same is true of the lemon odor, and it is true generally of the odor
components that enter into the "tastes" of food. Were the odor
components in these tastes as clear and distinct as they are when