CHAP, v.] TASTE AND SMELL. 1395 



cells differ from the cells forming the wall of the nest not only in 

 form but in chemical nature, and behave very differently from 

 them towards various reagents ; they stain with gold chloride for 

 instance very readily, and may with this reagent be prepared deeply 

 stained, while the walls of the nest and the rest of the epithelium 

 are hardly stained at all. 



In the dermis underlying the taste-buds, nerve fibres, derived 

 from the glosso-pharyngeal nerve, are abundant ; they may very 

 readily be seen in preparations of the papillae foliate. Some of these 

 are medullated and others sooner or later lose their medulla ; some 

 are distributed to parts other than the taste-buds, but some form at 

 the base of the taste-bud a plexus of non-medullated nerve filaments. 

 From this plexus, fibrils ascend into the substance of the bud and 

 are there lost to view. Some observers state that they have been 

 able to assure themselves of the continuity of the fibrils with the 

 central processes of the rod cells. Be this as it may, the existence 

 of the taste-bud is dependent on its connection, in some manner 

 or other, with the nerve fibres. If the glosso-pharyngeal nerve be 

 divided, and regeneration of the nerve prevented, the rod cells 

 and subsidiary cells degenerate and vanish, and finally the whole 

 taste-bud disappears. There can be no doubt that the specialized 

 cells are in some way the functional endings of the nerve. 



The small albuminous glands occurring as we have said in the 

 mucous membrane of the mouth are especially abundant in the 

 neighbourhood of the taste-buds ; they serve to supply fluid for the 

 solution of substances to be tasted, and as we shall presently see 

 such a solution seems to be a necessary condition for the activity 

 of the sensory organs. The dermis in the neighbourhood of the 

 taste-bud is always very vascular, and venous plexuses, assuming 

 almost the form of venous sinuses, are not infrequent; such a 

 venous sinus is conspicuous in the central ridge of a fold of a 

 papilla foliata. 



Taste-buds are found in other parts of the mouth besides the 

 hind part of the tongue, where as we have said they occur on 

 the fungiform and circumvallate papillas. They are found in the 

 soft palate, and in not inconsiderable numbers on the hinder 

 surface of the epiglottis. They are absent or extremely rare in 

 the front part and sides of the tongue. Their distribution in fact 

 appears not to coincide exactly with that of the sense of taste itself; 

 and we may therefore conclude that gustatory nerve fibres have 

 other terminations besides taste-buds. The only other mode 

 of termination however of which we are at present aware, is 

 that mode by which the nerve fibres, breaking up into fibrillse, 

 are lost among the cells of the epithelium without ending dis- 

 tinctly in any specially modified cell ; but this mode of termination 

 we shall study more closely in dealing with the sense of touch. 



It is obvious that a very complete analogy exists between the 

 taste-buds and the endings of the olfactory nerve. The rod cells 



F. 89 



