The
reason is, that the tip of the tongue is supplied only with nerves which
are really nerves of touch, not nerves of taste proper; they belong to a
totally different main branch, and they go to a different centre in the
brain, together with the very similar threads which supply the nerves
of smell for mustard and pepper. That is why the smell and taste of
these pungent substances are so much alike, as everybody must have
noticed, a good sniff at a mustard-pot producing almost the same
irritating effects as an incautious mouthful. As a rule we don't
accurately distinguish, it is true, between these different regions of
taste in the mouth in ordinary life; but that is because we usually roll
our food about instinctively, without paying much attention to the
particular part affected by it. Indeed, when one is trying deliberate
experiments in the subject, in order to test the varying sensitiveness
of the different parts to different substances, it is necessary to keep
the tongue quite dry, in order to isolate the thing you are
experimenting with, and prevent its spreading to all parts of the mouth
together. In actual practice this result is obtained in a rather
ludicrous manner--by blowing upon the tongue, between each experiment,
with a pair of bellows. To such undignified expedients does the pursuit
of science lead the ardent modern psychologist. Those domestic rivals of
Dr. Forbes Winslow, the servants, who behold the enthusiastic
investigator alternately drying his tongue in this ridiculous fashion,
as if he were a blacksmith's fire, and then squeezing out a single drop
of essence of pepper, vinegar, or beef-tea from a glass syringe upon the
dry surface, not unnaturally arrive at the conclusion that master has
gone stark mad, and that, in their private opinion, it's the microscope
and the skeleton as has done it.
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