Chap, v.] TASTE AND SMELL. 1035 



the terminal organs for tactile sensations, and from the structures 

 Avhatever they may be which are concerned in general sensibility. 

 Further, we have a certain amount of evidence that these ter- 

 minal organs are at least chiefly present in the fungiform and 

 circumvallate papillae. By careful manipulation it is possible, 

 under a lens, by means of a finely pointed brush to limit the 

 application of a minute drop of a sapid liquid, such as syrup, 

 solution of quinine and the like to a single papilla, and to 

 appreciate the sensation thus caused before the material has had 

 time to spread by diffusion. When this is done, it is found that 

 taste sensations are readily produced if the sapid substance 

 be applied to a papilla, but not at all or less readily if it be 

 applied between the papillae. Further, some papillae are found 

 especially sensitive to sweet, or to bitter or to acid substances, 

 or to two of these to the exclusion of the other. And somewhat 

 similar results are obtained by a limited application of the electric 

 current. Since the taste-buds are especially developed on these 

 circumvallate and fungiform papillae, we may infer that the name 

 taste-bud has been wisely chosen. But the development of taste 

 sensations, including bitter sensations, at the tip of the tongue, 

 from which taste-buds are said to be absent, presents a difficulty. 

 Unless we suppose that taste-buds, though often absent from 

 the tip of the tongue, are present in those cases in which sensations 

 are developed, we must conclude that gustatory sensations may 

 originate by the help of some kind of nerve ending other than 

 that of taste-buds. It might be suggested that bitter and sweet 

 tastes are developed by means of taste-buds and acid and salt 

 tastes by means of other endings 3 but there is no satisfactory 

 evidence of this. 



§ 643. The question which nerve or nerves subserve taste 

 and what is the course of the gustatory fibres is one which pre- 

 sents great difficulties. The front surface of the tongue is sup- 

 plied by the lingual or gustatory branch of the fifth nerve, the 

 hind surface by the glossopharyngeal nerve, which nerve also 

 supplies the soft palate, though a branch (palatine) of the fifth 

 nerve goes there also. The nerves traced to the taste-buds in the 

 papillae foliatee and circumvallatae belong to the glossopharyn- 

 geal nerve, and it can hardly be doubted that gustatory fibres 

 run in the branches of that nerve which go to the back of the 

 tongue. On the other hand in the cases in which sensations 

 are distinctly developed in the tip of the tongue we must infer 

 that gustatory fibres run in the lingual branch of the fifth, since 

 no glossopharyngeal fibres are distributed to this part of the 



tongue. 



But it by no means follows from this that gustatory fibres 

 pass straight both up the trunk of the glossopharyngeal nerve, 

 and up the trunk of the fifth nerve to their respective nuclei in 

 the bulb. 



