ii 4 VETERINAKY PHYSIOLOGY 



pharyngeal nerve. The anterior two-thirds are supplied by 

 the lingual of the fifth and the chorda tympaui of the seventh. 

 It has been maintained that all these fibres enter the medulla by 

 way of the Gasserian ganglions and the root of the fifth nerve ; 

 but the study of cases in which the ganglion has been removed 

 does not support this view, and the evidence seems to indicate 

 that the fibres enter the medulla by the roots of the nerve 

 in which they run. 



The position of the receiving centre in the brain is con- 

 sidered on p. 205. 



3. Physiology. As to the way in which this mechanism 

 is stimulated our knowledge is very imperfect. In order to 

 act, the substance must be in solution. The strength of the 

 sensation depends on the concentration of the solution, upon 

 the extent of the surface of the tongue acted upon, upon 

 the duration of the action, and upon the temperature of 

 the solution. If the temperature is very high or very low 

 the taste sensation is impaired by the feelings of cold or 

 heat. 



It is most difficult to classify the many various taste sensa- 

 tions which may be experienced, but they may roughly be 

 divided into four main groups : 



1. Sweet. 3. Acid. 



. 2. Bitter. 4. Saline. 



"Whether different sets of terminations react specially to 

 each of these is not known, but it has been found that sub- 

 stances giving rise to the sensation which we call bitter act 

 best on the back of the tongue, while substances producing 

 sweet or acid sensations act on the sides and front. Again, 

 chewing the leaves of gymnema sylvestre abolishes sensations 

 of sweet and bitter, but does not interfere with those of acid 

 and saline, and leaves the tactile sense unimpaired. On the 

 other hand, cocaine paralyses the tactile sense before it inter- 

 feres with the sense of taste. 



The sense of taste is very closely connected with the sense 

 of smell, and, when the latter is interfered with, many sub- 

 stances seem tasteless which under normal conditions have a 

 marked flavour. 



