TASTE.
The sense of taste is directly connected with the preservation and nutrition of the body. A delicious flavor produces a desire to eat a savory substance. Some writers on hygiene have given this sense an instinctive character, by assuming that all articles having an agreeable taste are suitable for diet. The nerves of taste are distributed over the surface of the tongue and palate, and their minute extremities terminate in well developed papillæ. These papillæ are divided into three classes, termed, from their microscopic appearance, filiform, fungiform and circumvallate. The organ of taste is the mucous membrane which covers the back part of the tongue and the palate. The papillæ of the tongue are large and distinct, and covered with separate coats of epithelium. The filiform papillæ are generally long and pointed and are found over the entire surface of the tongue. The fungiform are longer, small at the base and broad at the end. The circumvallate are shaped like an inverted V and are found only near the root of the tongue; the largest of this class of papillæ have other very small papillæ upon their surfaces. It is now pretty satisfactorily established that the circumvallate, or fungiform papillæ 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.