THE SENSE OF TASTE. 553 



the lingual branch of the fifth nerve is the seat of sensations of 

 taste in the anterior part of the tongue: and it is also certain, 

 from the marked manifestations of pain to which its division 

 in animals gives rise, that it is likewise a nerve of common sen- 

 sibility. The glosso-pharyngeal also seems to contain fibres 

 both of common sensation and of the special sense of taste. 



The concurrence of common and special sensibility in the 

 same part makes it sometimes difficult to determine whether 

 the impression produced by a substance is perceived through 

 the ordinary sensitive fibres, or through those of the sense of 

 taste. In many cases, indeed, it is probable that both sets of 

 nerve-fibres are concerned, as when irritating acrid substances 

 are introduced into the mouth. 



The impressions on the mind leading to the perception of 

 taste seem to result, as already said, from certain changes in 

 the internal condition of the nerves produced by the contact 

 of sapid substances with the papillae in which the fibres of these 

 nerves are distributed. This explanation, obscure though it 

 be, may account generally for the sense ; but the variations of 

 taste produced by different substances are as yet inexplicable. 

 In the case of hearing, we know that sounds differ from one 

 another according to the differences in the number of undula- 

 tions producing them ; and in the case of vision, it is reasonably 

 inferred that different colors result from differences in the num- 

 ber of undulations, or in the rate of transit, of the principle of 

 light. But, in the cases of taste and smell, no such probable 

 explanation has yet been offered. It would appear, indeed, 

 from the experiments of Horn, that while some substances 

 taste alike in all regions of the tongue's surface, others excite 

 different tastes, according as they are applied to different pa- 

 pillae of the tongue. This observation, if confirmed, would 

 seem to show that, in some cases at least, different fibres are 

 capable of receiving different impressions from the same sapid 

 substance. 



Much of the perfection of the sense of taste is often due to 

 the sapid substances being also odorous, and exciting the sim- 

 ultaneous action of the sense of smell. This is shown by the 

 imperfection of the taste of such substances when their action 

 on the olfactory nerves is prevented by closing the nostrils. 

 Many fine wines lose much of their apparent excellence if the 

 nostrils are held close while they are drunk. 



Very distinct sensations of taste are frequently left after the 

 substances which excited them have ceased to act on the nerve ; 

 and such sensations often endure for a long time, and modify 

 the taste of other substances applied to the tongue afterwards. 

 Thus, the taste of sweet substances spoils the flavor of wine, 



