734 



SMELL 



[CH. LI II. 



It will thus be seen that there are many facts pointing to the 

 conclusion, that the varieties of gustatory like those of cutaneous 

 sensation are due to the stimulation of different end organs. 



When diluted sweet and salt solutions are simultaneously applied 

 to the tongue, they tend to neutralise one another, but a true indifferent 

 point is difficult or impossible to reach. Sweet and bitter, sweet and 

 acid-tasting substances are antagonistic to a similar but less perfect 

 extent. Contrast-effects of one taste upon another are matters of 

 common observation, but can only be experimentally investigated with 

 great difficulty. 



Smell. 



The entrance to the nasal cavity is lined with a mucous membrane 

 closely resembling the skin. The greater part of the rest of the 



cavity is lined with ciliated epi- 

 thelium; the corium is thick and 

 contains numerous mucous glands. 

 The olfactory region in man is 

 limited to a portion of the mem- 

 brane covering the upper turbinal 

 bone, and is only 245 square milli- 

 metres in area. This area is larger 

 in animals with a keener sense of 

 smell than we possess. The cells 

 of the epithelium here are of several 

 kinds: first, columnar cells not 

 ciliated (fig. 535, st), with the broad 

 end at the surface, and below 

 tapering into an irregular branched 

 process or processes, the termina- 

 tions of which pass into the next layer: the second kind of cell 

 (fig. 535, r) 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 process is very delicate and may be varicose. 

 The upper process is prolonged beyond the surface, where it becomes 

 stiff, and in some animals, like the frog, is provided with hairs. 

 These cells, which are called olfactorial cells, are numerous, and the 

 nuclei of the cells not being on the same level, a comparatively 

 thick nuclear layer is the result (fig. 537, b). In the corium are 

 a number of serous glands called Bowman's glands. They open 

 upon the surface by fine ducts passing up between the epithelium 

 cells. 



FIG. 535. Cells from the olfactory region of 

 the rabbit, st, Supporting cells ; r, r 1 , 

 olfactorial cells ; /, ciliated cells ; s, cilia- 

 like processes ; b, cells from Bowman's 

 gland. (Stohr.) 



