864 



OF SENSATION, AND THE ORGANS OF THE SENSES. 



of the saliva. And, as Dr. Baly has pointed out, 1 "if the end of the finger 

 be made to strike quickly, but lightly, the surface of the tongue at its tip, or 

 its edge near the tip, so as to affect not the substance of the organ, but merely 

 the papillae, a taste sometimes acid, sometimes saline, like the taste produced by 

 electricity, will be distinctly perceived. The sensation of taste thus induced 

 will sometimes continue several seconds after the application of the mechanical 

 stimulus." On the other hand, as Wagner has truly remarked, if the surface 

 of the tongue near the root be touched with a clean dry glass rod, or a drop of 

 distilled water be placed upon it, a slightly bitterish sensation is produced ; and 

 this, if the pressure be continued, passes into that of nausea, and, if the pres- 

 sure be increased, even excites vomiting. The feeling of nausea may be excited 

 by mechanical irritation of any part of the surface of the fauces and soft palate ; 

 and this feeling is certainly much more allied to that of taste than to that of 

 touch. Further, it has been observed by Henle that, if a small current of air 

 be directed upon the tongue, it gives rise to a cool saline taste like that of salt- 

 petre. Thus we find that the peculiar effects of sapid substances upon the 

 nerves of taste may be imitated to a certain extent by other agencies ; and it 



also appears that the sensations excited 



Fig. 197. by these vary according to the part of 



the gustative surface on which they 

 operate ; mechanical or electrical stimu- 

 lation of the front of the tongue giving 

 rise to a kind of saline taste, whilst 

 mechanical stimulation applied to the 

 back of the tongue and fauces excites 

 the feelings of bitterness and nausea. 

 One of the conditions requisite for the 

 due exercise of the gustative sense is a 

 temperature not departing far on either 

 side from that which is natural to the 

 body. It appears from the recent ex- 

 periments of Prof. E. H. Weber, 3 that if 

 the tongue be kept immersed for nearly 

 a minute in water of about 125, the 

 taste of sugar brought in contact with 

 it, either in powder or solution, is no 

 longer perceived ; the sense of touch, 

 usually so delicate at the tip of the 

 tongue, being also rendered imperfect. 

 A similar imperfection of taste and 

 touch was produced by immersing the 

 tongue for the same length of time in 

 a mixture of water and broken ice. 



869. The surface of the tongue is 

 undoubtedly the special seat of gusta- 

 tive sensibility in Man; though the 

 sense of Taste is not by any means 

 restricted to that organ, being diffused 

 in a less degree over the soft palate, 

 the arches of the palate, and the fauces. 

 It is on the Tongue alone, however, 

 that the papillary apparatus is fully 



Tongue seen on its upper surface : a. One of the 

 "circumvallate papillae. 6. One of the fungiform 

 papillae. Numbers of the conical papillae are seen 

 about d, and elsewhere, e. Glottis, epiglottis, and 

 glosso-epiglottidean folds of mucous membrane. 

 From Soemmering. 



1 Translation of "Miiller's Physiology," p. 1062, note. 



2 "Muller's Arclriv.," 1847, S. 342. 



