608 



THE SENSES 



tongue, and acids along the sides. Individual tests of the fungiform papillae 

 by Oehrwall showed that about half the papillae reacted to sweet, bitter, 

 and acid, but that certain ones reacted only to sweet, or to sweet and bitter, 

 or to acid and bitter. This suggests the specific nature of the taste sensa- 

 tions and tends to prove that there may be a special organ for each kind of 

 stimulus. Experiments have also shown that it is possible to do away with 

 the power of tasting bitters and sweets while the taste for acids and salts 

 remains. This is done by chewing the leaves of an Indian plant, Gymnema 

 sylvestre. It has also been shown that the power of tasting sweet substances 

 disappears before that of tasting bitter. Other experiments have shown that 

 the mechanisms for salt and acid tastes are distinct. 



After-tastes and Contrasts. Verv distinct sensations of taste are 



FIG. 425. Localization of Taste. Bitter ; acid ; salt, ; sweet ; T, tonsils; 



FC, foramen cecum; CF, circumvallate papillae; FP, fungiform papillae. (Hall.) 



frequently left after the substances which excited them have ceased to act 

 on the nerve, as the after-taste of metallic bitter, which remains after breaking 

 the stimulating current. Such sensations often endure for a long time, and 

 modify the taste of other substances applied to the tongue. Thus, the taste 

 of swv^et substances is intensified after the tasting of common salt. After 

 rinsing the mouth with water containing salt, it is said that sweet solutions 

 are perceived that are too dilute to be detected ordinarily. Many other 

 chemicals produce similar results. The application of a sapid substance, 

 acid for example, to one side of the tongue intensifies the sensation produced 

 by a sapid substance applied to the other side. There is a simultaneous con- 

 trast which suggests that the same relation exists between tastes as between 

 colors, of which those that are opposed, i.e., complementary, render each 



