CHAP, v.] TASTE AND SMELL. 263 



those regions only in which they experience bitter and sweet 

 tastes. 



We have already said that bitter and sweet tastes seem to be 

 on a different footing from acid and salt tastes ; and w r e have a 

 certain amount of evidence that the two former sensations are 

 brought about by means of terminal* organs different from jthose 

 by means of which the two latter are brought about. If some of 

 the leaves of a plant which grows in India and is called Gymnema 

 sylvestre, be chewed, or if the mouth be washed with a decoction 

 of the leaves, for some little time afterwards bitter and sweet 

 tastes are lost, neither quinine nor sugar exciting the usual sen- 

 sations, though acid and salt tastes remained unaffected. We may 

 interpret this result as indicating that the drug in some way or 

 other ' paralyses,' that is to say, suspends the action of, the terminal 

 organs, whatever they may be, by means of which bitter and sweet 

 tastes are developed, but leaves untouched those by which other 

 gustatory sensations are developed. The action of the same drug 

 supports the further conclusion that the terminal organs of bitter 

 tastes are different from those of sweet tastes ; since by using an 

 adequately weak dose of the drug the sweet taste may be abolished 

 while the bitter taste remains distinct. 



Indeed it is probable that the distribution of the several kinds 

 of tastes over different regions of the mouth, which we mentioned 

 above, is dependent on the distribution of different kinds of 

 terminal organs ; it is probable that we experience bitter tastes 

 by means of the back of the tongue because the terminal organs of 

 the bitter taste are limited to, or at least most abundant in, the 

 back of the tongue, those of the sweet taste by the front of the 

 tongue because the terminal organs of the sweet taste are more 

 abundant there ; and so on. If a small quantity of a particular 

 bromine derivative of the . substance which from its remarkably 

 sweet taste has been called ' saccharine,' be placed carefully on the 

 tip of the tongue, a sweet taste is developed; but if the same 

 substance be carefully placed on the back of the tongue the result 

 is not a sweet but a bitter taste. At least this is the result in 

 the case of those individuals who taste bitter at the back of, and 

 sweet at the tip of, the tongue. From this we may infer that, in 

 such tongues, the specific terminal organs of the sweet taste are 

 more or less completely limited to the front, and those of the 

 bitter taste to the back of the tongue, both sets of terminal 

 organs being of such a nature that while quinine affects the one 

 only and sugar the other only, the substance of which we are 

 speaking is able to affect both of them. In a somewhat similar 

 way certain salts, magnesium sulphate for instance, when applied 

 to the back of the tongue excite a bitterish taste, but when 

 applied to the tip of the tongue excite an acid or a sweetish acid 

 taste. 



We said a little while back that a weak interrupted current, 



