CHAP, in.] HEARING, SMELL, AND TASTE. 571 



either the glossopharyngeal or lingual nerves, would give rise to a 

 sensation of taste and nothing else, the proof is not forthcoming ; 

 since both these nerves are mixed nerves containing other afferent 

 fibres as well as those of taste. 



When the constant current is used as a means of exciting taste, 

 gustatory sensations are found to be developed in the back, edges 

 and tip of the tongue, the soft palate, the anterior pillar of the 

 fauces, and a small tract of the posterior part of the hard palate. 

 They are absent from the anterior and middle dorsal, and under 

 surface of the tongue, the front portion of the hard palate, the 

 posterior pillars of the fauces, the gums and the lips. Sapid 

 substances are unsuitable as a test for this purpose, on account of 

 their rapid diffusion. Bitter substances produce most effect when 

 placed on the back of, and sweet substances when placed on the tip 

 of the tongue ; but the tasting power of the tip of the tongue varies 

 very much in different individuals and in many seems almost 

 entirely absent. It is said that acids are best appreciated by the 

 edge of the tongue. 



It is essential for the developement of taste, that the substance 

 to be tasted should be dissolved ; and the effect is increased by 

 friction. The larger the surface the more intense 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. 

 The nerves of taste are, as we have said, the glossopharyngeal and 

 the lingual or gustatory. The former supplies the back of the 

 tongue, and section of it destroys taste in that region. The latter 

 is distributed to the front of the tongue, and section of it similarly 

 deprives the tip of the tongue of taste. There is no reason for 

 doubting that the gustatory fibres in the glossopharyngeal are 

 proper fibres of that nerve ; but it has been urged by many, that 

 the gustatory fibres of the lingual are derived from the chorda 

 tympani, and that those fibres of the lingual which come from the 

 fifth are employed exclusively in the sensations of touch and 

 feeling; the evidence in favour of this view is however incon- 

 clusive. 



