852 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



fined to the fungiform papillae, seen often as red dots scattered over the upper 

 surface ; to the circumvallate papillae, the pores of the buds opening into the 

 groove around the papilla; and to an area just in front of the anterior pillar 

 of the fauces, which somewhat resembles the papilla foliata of the rabbit. 



The sensory nerves distributed to the tongue include filaments from the 

 glosso-pharyngeal, the lingual branch of the fifth, and the chorda tympani. 

 The relation of these nerves to the sense of taste has been the occasion of 

 much dispute. The weight of evidence probably favors the belief that the 

 glosso-pharyngeal is the nerve of taste for the posterior third of the tongue, 

 while the lingual and, to some extent, the chorda carry taste-impressions from 

 the anterior two-thirds. Clinical cases have been cited to show that all the 

 gustatory fibres arise from the brain as part of the glosso-pharyngeal nerve, 

 whatever may be their subsequent course to the tongue. On the contrary, 



other cases have shown a marked loss 

 of taste-sensation following upon lesions 

 of the fifth nerve at or near its origin 

 from the brain, while still others indi- 

 cate that some of the taste-fibres may 

 arise in the seventh nerve. The point 

 is of practical importance in diagnosis, 

 in the interpretation of loss of taste 

 over any given part of the tongue, but 

 the contradiction in the clinical cases 

 reported has led to the general belief 

 that the origin and course of the gusta- 

 tory fibres are subject to considerable 

 individual variations. 



Our taste-perceptions are ordinarily 

 much modified by simultaneous olfac- 

 tory sensations, as may easily be dem- 

 onstrated by the difficulty experienced 

 in distinguishing by taste an apple, an 

 onion, and a potato, when the nostrils are closed. Sight has also an import- 

 ant influence, at least in quickening the expectancy for individual flavors. 

 Every smoker knows the blunting of his perception for burning tobacco 

 while in the dark ; various dishes having distinctive flavors are said to lose 

 much of their gustatory characteristics when the eyes are bandaged. 



The intensity of gustatory sensation increases with the area to which the 

 tasted substance is applied. The movements of mastication are peculiarly 

 adapted to bring out the full taste value of substances taken into the mouth, 

 and the act of swallowing, by which the morsel is rubbed between the tongue 

 and the palate, has been proved to develop tastes not appreciable by simple 

 contact with the sensory surface. A considerable area in the mid-dorsum of 

 the tongue is said to be devoid of all taste-sensibility. 1 



1 Shore : Journal of Physiology, 1892, vol. xiii. p. 191. 



FIG. 293. Section through one of the taste-buds 

 of the papilla foliata of the rabbit (from Quain, 

 after Ranvier), highly magnified: p, gustatory 

 pore ; s, gustatory cell ; r, sustentacular cell ; m, 

 leucocyte containing granules; e, superficial epi- 

 thelial cells ; n, nerve-fibres. 



