TASTE AND SMELL. 



[CH. LII. 



(Gymuerna sylvestre) to do away with the power of tasting 

 bitters and sweets, while the taste for acids and salts remains. 



The delicacy of the sense of taste is sufficient to discern i part 

 of sulphuric acid in 1,000 of water. The sense may be improved 

 by practice, as in professional tea-tasters. 



Smell. 



Here again we shall take anatomical considerations before 

 studying the physiology of the sense of smell. 



The nasal cavities are divided into three districts : 



(a) Regio vestibularis \ this 

 is the entrance to the cavity ; 

 it is lined with a mucous meltn- 

 brane closely resembling the 

 skin, and contains hairs (vi- 

 brissce) with sebaceous glands. 



(b) Regio respiratoria in- 

 cludes the lower meatus of the 

 nose, and all the rest of the 

 nasal passages except (c) ; its 

 mucous membrane is covered 

 by ciliated epithelium. The 

 corium is thick and consists 

 of fibrous connective-tissue ; it 

 contains a certain number of 



Fig. 532. Cells from the olfactory region of 

 the rabbit, st, supporting cells ; r, r', 

 olfactprial cells ; /, ciliated cell ; *, 

 cilia-like processes ; b, cells from Bov- 

 man's gland. (Stohr.) 



mucous and serous 



tubular 



glands. 



(c) Regio olfactoria, includes the anterior two-thirds of the 

 superior meatus, the middle meatus, and the upper half of the 

 septum nasi. It is considerably larger in animals like the dog, 

 with a keener sense of smell than we possess. It consists of 

 a thicker mucous membrane than in (b), made up of loose areolar 

 connective-tissue covered by epithelium of a special variety, 

 resting upon a basement membrane. The cells of the epithelium 

 are of several kinds : first, columnar cells not ciliated (fig. 532, st), 

 with the broad end at the surface, and below tapering into an 

 irregular branched process or processes, the terminations of which 

 pass into the next layer : the second kind of cell (fig. 532,*-) consists 

 of a small cell body with large spherical nucleus, situated between 

 the ends of the first kind of cell, and sending upwards a process to 

 the surface between the cells of the first kind, and from the other 

 pole of the nucleus a process towards the corium. The latter pro- 

 cess is very delicate and may be varicose. The upper process 

 is prolonged beyond the surface, where it becomes stiff, and in 



