CHAP, v.] TASTE AND SMELL. 261 



course in either the above two nerves will produce sensations 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. 



866. It is essential for the development of taste, that the 

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

 the glands, which as we have seen 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 

 substances 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 distinct 

 sensations when rubbed between the tongue and the soft palate ; 

 indeed we generally make use of this movement known as " smack- 

 ing 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 sensitive 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 remain- 

 ing 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 quinine 

 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 different kind, 

 is frequently influenced by its predecessor, being sometimes aug- 

 mented, 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 localisation. When we place 

 quinine in our mouth, the resulting sensation of taste gives us no 

 information as to where the quinine is, though we may learn that 

 by concomitant general sensations arising in the buccal mucous 

 membrane. And it must be remembered that all our gustatory 

 sensations are always accompanied by tactile or other sensations. 

 We do not, as in the case of smell, experience the specific sensation 



