Chap, v.] TASTE AND SMELL. 1031 



sensations was uncertain. We have no satisfactory evidence 

 whatever that direct stimulation of the gustatory fibres along 

 their course in either the above two nerves will produce sensa- 

 tions of taste. As far as the sense of taste is concerned we 

 have no adequate evidence that specific gustatory impulses can 

 be developed in the gustatory fibres apart from changes in the 

 nerve endings. But the evidence is negative only ; and the 

 case is one not suited for experiment, since both nerves along 

 their whole course are mixed nerves containing other afferent 

 fibres than those of taste. 



§ 641. It is essential for the development of taste, that the 

 substance to be tasted should be dissolved; hence, the value of 

 the glands, which are especially abundant in the neighbourhood 

 of the taste-buds. The effect is also increased by friction ; and 

 the tongue and lips may be regarded as a subsidiary apparatus 

 which by their movements assist in bringing the sapid sub- 

 stances into contact with the mucous membrane of the mouth. 

 A substance may give rise to hardly any sensation of taste when 

 simply placed on the extended tongue, and yet excite very dis- 

 tinct sensations when rubbed between the tongue and the soft 

 palate ; indeed we generally make use of this movement known 

 as "smacking the lips," when we desire to obtain strong taste 

 sensations. In this act however we not only make use of the 

 most sensitive surfaces and call in the aid of friction, but we 

 also increase the sensation by employing a large area of sensi- 

 tive surface; for the larger the surface the more intense is the 

 sensation. 



The sensation takes some time to develope, and endures for 

 a long time, though this may be in part due to the stimulus 

 remaining in contact with the terminal organs. 



A temperature of about 40° is the one most favourable for 

 the production of the sensation. At temperatures much above 

 or below this, taste is much impaired. A weak solution of qui- 

 nine readily tasted at the normal temperature of the mouth is 

 not tasted if, immediately before, very cold or very hot water be 

 held in the mouth for a little while. 



We may experience at the same time coincident taste sensa- 

 tions of different kinds, such for instance as one of bitterness 

 with one of saltness ; but in some cases one sensation interferes 

 with the other, as for instance bitterness and sweetness. A 

 taste sensation following upon a previous sensation of a differ- 

 ent kind, is frequently influenced by its predecessor, being 

 sometimes augmented, sometimes inhibited. 



Though we can hardly be said to project our sensations of 

 taste into the external world, as we do those of sight, hearing 

 and smell, we assign to them no subjective localization. When 

 we place quinine in our mouth, the resulting sensation of taste 

 gives us no information as to where the quinine is, though we 



