642 



THE SENSES 



are especially developed at the tip and sides of the tongue, while bitter tastes 

 are almost absent in the front, but especially developed on the basal region, 

 and in the fauces and pharynx. Salts are more stimulating to the tip of the 

 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 sensations 

 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 mech- 

 anisms for salt and acid tastes are distinct. 



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



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



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

 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 sweet 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- 



