516 THE NERVOUS SYSTEM. 



such as the animal and vegetable juices and the soluble salts. Saline 

 substances which are insoluble, such as calomel or lead carbonate, pro- 

 duce no gustatory impression. 



The mechanism of taste is, in all probability, direct and simple. The 

 sapid substances in solution are absorbed by the lingual papillae, and, 

 coming in contact with the terminal nervous filaments, excite sensibility 

 by uniting with their substance. The rapidity with which endosmosis 

 will take place under certain conditions is sufficient to account for the 

 quick perception of sapid substances introduced into the mouth. 



It is on this account that free secretion of saliva is favorable to 

 the gustatory function. If the mouth be dry, food has but little taste. 

 But when the saliva is freely secreted, it is mixed .with the food in 

 mastication, assisting the solution of its sapid ingredients ; and the 

 fluids of the mouth, impregnated with the savory substances, are ab- 

 sorbed by the mucous membrane and excite the gustatory nerves. 



An important part is taken in this process by the movements of the 

 tongue. By these movements the food is carried from one -part of 

 the mouth to another, compressed against the mucous membrane, its 

 solution assisted, and the penetration of fluids into the papillae more 

 rapidly accomplished. If powdered sugar, or a semi-solid bitter ex- 

 tract, be simply placed upon the dorsum of the tongue, little or no 

 effect is produced ; but when pressed by the tongue against the roof 

 of the mouth, in the movements of eating or drinking, its taste is 

 immediately perceived. This is explained by the well-known fact that 

 movement and friction facilitate the liquefaction and imbibition of 

 soluble substances. The nervous papillae of the tongue may therefore 

 be regarded as the essential instruments of taste, and the lingual 

 muscles as its accessory organs. 



Impressions of taste made upon the tongue remain for a certain 

 time afterward. When a very sweet or a very bitter substance is 

 taken into the mouth, its taste is retained for several seconds after it 

 has been ejected or swallowed. Consequently, if 'different savors be 

 presented to the tongue in rapid succession, they become undistinguish- 

 able, and produce only a confused combination of several impressions. 



If the substance first tasted have a particularly marked savor, its 

 impression will preponderate over that of the others. A similar effect 

 is produced by substances which excite the general sensibility of the 

 tongue, such as acrid or stimulating powders ; and it belongs, in the 

 greatest degree, to substances which are at the same time sapid, pun- 

 gent, and aromatic, like sweetmeats flavored with the volatile oils. 

 Advantage is sometimes taken of this in the administration of disagree- 

 able medicines. By first taking into the mouth some highly flavored 

 and pungent substance, nauseous drugs may be immediately swallowed 

 with but little perception of their qualities. 



