204 



THE HUMAN BODY 



it is fatigued. One may notice a bad odor upon entering a room, 

 but in a few minutes ceases to perceive it because his olfactory 

 apparatus has become fatigued. For this reason the sense of 

 smell is wholly untrustworthy as a guide by which to regulate 

 the ventilation of a room. 



Taste. The organ of taste is the mucous membrane on the 

 dorsum of the tongue * and, in some persons, of the soft palate 

 and fauces. The nerves concerned are the glossopharyngeals, 

 distributed over the hind part of the tongue, and the lingual 

 branches of the. inferior maxillary division of the trigeminals 

 on its anterior two-thirds. It has been shown that the nerves 

 of taste which reach the tongue by way of the trigeminal 

 nerve spring from the medulla as part of the sensory branch 

 of the facial. 



On the tongue most of the sensory nerves run to papillae; the 

 circumvallate have the richest supply, and on these are peculiar 



FIG. 77. Taste-buds. 



end organs (Fig. 77) known as taste-buds; they are oval and em- 

 bedded in the epidermis covering the side of the papilla. Each 

 consists, externally, of a number of flat, fusiform, nucleated cells 

 and, internally, of six or eight so-called taste-cells. The latter are 

 much like the olfactory cells of the nose, and are probably con- 

 nected with nerve-fibers at their deeper ends. The capsule formed 

 by the enveloping cells has a small opening on the surface; each 

 taste-cell terminates in a very fine thread which there protrudes. 

 Taste-buds are also found on some of the fungiform papillae, and 

 it is possible that simpler structures, not yet recognized, and con- 



* A description of the tongue will be found on p. 400. 



