ed V and are found only near the
root of the tongue; the largest of this class of papillae have other
very small papillae upon their surfaces. It is now pretty satisfactorily
established that the circumvallate, or fungiform papillae are the only
ones concerned in the special sense of taste.

The conditions necessary to taste are, that the substance be in solution
either by artificial means, or by the action of the saliva; and that it
be brought in contact with the sensitive filaments imbedded in the
mucous membrane. The nerves of taste are both _general_ and _special_ in
their functions. If the general sensibility of the nerves of taste is
unduly excited, the function of sensibility is lost for some time. If a
peppermint lozenge is taken into the mouth, it strongly excites the
general sensibilities of taste, and the power of distinguishing between
special flavors is lost for a few moments. A nauseous drug may then be
swallowed without experiencing any disagreeable taste.

Paralysis of the facial nerve often produces a marked effect in the
sensibility of the tongue. Where this influence lies has not been fully
explained; probably it is indirect, being produced by some alteration in
the vascularity of the parts or a diminution of the salivary secretions.

TOUCH.

By the sense of touch, we mean the _general sensibility of the skin_.
Sensations of heat and cold are familiar illustrations of this faculty.
By the sense of touch, we obtain a knowledge of certain qualities of a
body, such as form consistency, roughness, or smoothness of surface,
etc. The tip of the tongue possesses the most acute sensibility of any
portion of the body, and next in order are the tips of the fingers. The
hands are the principal organs of tactile sensation. The nerves of
general sensibility are distributed to every part of the cutaneous
tissue. The contact of a foreign body with the back, will produce a
similar _tactile_ sensation, as with the tips of the fingers. The
sensation, however, will differ in _degree_ because the back is supplied
with a much smaller number of sensitive filaments; in _quality_ it is
the same.

* * * * *

CHAPTER XIV.

CEREBRAL PHYSIOLOGY.

By means of the nervous system, an intimate relation is maintained
between mind and body, for nervous energy superintends the functions of
both. The fibres of nervous matter are universally present in the
organization, uniting the phy