THE SENSE OF TASTE. 



411 



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Fig. 206.— Section through one of the taste-buds 

 of the papilla foliata of the rabbit (from Quain, 

 after Ranvier), highly magnified: p, gustatory 

 pore ; «, gustatory cell ; r, sustentacular cell ; in, 

 leucocyte containing granules; e, superficial epi- 

 thelial cells ; a, nerve-fibres. 



gustatory fibres arise from the brain as part of the glossopharyngeal 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. In the condition of anosmia 

 the ability to discriminate between tastes is much below par. Sight has also 

 an important 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 eves are bandaged. 1 



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. 2 



The sensitiveness of taste-sensation is greatest when the exciting substance 

 is at the temperature of the body. Weber 3 found that when the tongue was 

 dipped during one-half to one minute in water either at the freezing tempera- 

 ture or warmed to 50° C, the sweet taste of sugar could no longer be appre- 

 ciated by it. It is probable that sapid substances reach the sensory endings 

 of the nerves of taste only after being dissolved in the natural fluids of the 

 mouth, and any artificial drying of the buccal surfaces or alteration of their 

 secretion must affect taste-perceptions. 



1 Cf. Patrick: "Studies in Psychology," Univ. Iowa, 1899, vol. ii. 

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

 3 Archivfiir Anaiomie wnd Physiologie, is 17, S. 'M2. 



