740 PHYSIOLOGY. 



Varieties of Substances. Of the gustatory substances there are 

 four: (1) sweety (2) bitter, (3) acid, and (4) saline. In addition 

 to these fundamental substances there are compound gustatory im- 

 pressions, or a confusion of gustatory sensations with those which are 

 tactile or olfactory. Thus, there is known the piquant taste of 

 cheese, the caustic taste of mustard, and the aromatic taste of 

 strawberries. 



The acid and sweet tastes are best perceived at the tip and edges 

 of the tongue; the salty and bitter tastes are comprehended at the 

 base. This leads to the result that some substances have a different 

 taste, dependent upon whether they touch the tip or the base of the 

 tongue. Thus, acetate of potassium at the tip of the tongue is acid, 

 and at the base it is bitter. 



Fig. 302. Sternberg's Gustometer. 



The four primitive tastes are not all perceived at the exact time 

 of their impression upon the tongue. The salty is first perceived, 

 then the sweet, next the acid, and last the bitter. 



Tactile sensations by astringents (tannic acid) or thermal sensa- 

 tions (mustard) are usually confounded with taste proper. The taste 

 of vanilla is but an olfactory impression. 



Drugs. By the action of drugs one is able to abolish certain 

 tastes more readily than others. Cocaine upon the tongue abolishes 

 tactile sensations and the taste for bitter things, but does not inter- 

 fere with voluntary movement. 



The leaves of Gymnema sylvestre, when chewed, destroy the sense 

 of taste for bitters and sweets, while that for salts and acids remains. 



The Taste-center, to which the gustatory nerves send their im- 

 pressions, lies in the uncinate gyrus. 



Sternberg's Gustometer. This instrument consists of a Richard- 

 son double-bellows rubber bulb, which is attached to a two-way stop- 

 cock. The two-way stopcock is connected by rubber tubes with two 

 glass bulbs fitted with an entrance and an exit tube. Both glass 

 bulbs contain small pieces of sponge, to increase the surface fof 



