THE SENSE OF TASTE. 297 



possessing one or other of these tastes, by means of a fine camel- 

 hair brush to different portions of the tongue, after drying this 

 somewhat with a towel. Bitter taste is absent from all parts of 

 the tongue except the base, hence a mouthful of a, weak solution 

 of quinine sulphate has practically no taste until it is swal- 

 lowed, when however, it tastes intensely bitter. Sweet and sour 

 tastes are most acute at the tip and sides of the tongue. Saline 

 taste is more evenly distributed. 



This location of taste sensations is not a hard and fast one, 

 for neighboring taste buds in, say, the bitter area at the root of 

 the tongue may appreciate different tastes; thus, if a solution 

 containing quinine and sugar be applied to one papilla, it may 

 taste sweet, whereas when applied to a neighboring one, it tastes 

 bitter. With weak solutions one taste may neutralize another; 

 thus the addition of a small amount of salt to a weak sugar solu- 

 tion may remove its sweet taste. This neutralization of one 

 taste by another does not occur when the solutions are stronger ; 

 thus a mixture of acid and sugar, as in lemonade, causes stimu- 

 lation of both "acid" and "sweet" taste buds. The stimula- 

 tion of one kind of taste bud may cause other taste buds to be- 

 come more acutely sensitive, which explains the sweetish taste of 

 water after washing out the mouth with a solution of salt. 



Attempts have been made to correlate the chemical structure 

 of organic substances with the taste which they excite, but with 

 little success. Thus pure proteins have very little taste, whereas 

 half -digested protein is intensely bitter; on the other hand, the 

 pure amino acids, which form a large proportion of the de- 

 composition products in such a digest, are sweet. In the case of 

 acids and alkalies, however, it has been established that the acid 

 taste is due to the H-ion and the alkaline to the OH-ion. Some 

 acids, such as acetic, taste more acid than we should expect from 

 their degree of dissociation into H-ions. This is because of 

 their power of penetration into the cells of the taste buds. When 

 platinum terminals from a battery are applied to the tongue, 

 the positive pole tastes alkaline and the negative acid, because 

 OH-ions accumulate at the former and H-ions at the latter. 



ASSOCIATION BETWEEN TASTE, TOUCH AND SMELL. But the 



