176 



ADVANCED PHYSIOLOGY 



pharynx, or throat. The main current of air does not enter 

 the spaces high up in the nose, between and somewhat below 

 the level of the eyes, yet it is the lining of these upper passages 

 that is especially constructed for smelling. The two chief 

 kinds of cells in this lining are: mucous cells, which are cylin- 

 drical and rather large, and 

 the true olfactory cells, which 

 are slender and rod-like; Fig. 

 97. 



Just what happens to the 

 olfactory cells when scented 

 air enters the nose, is not 

 known; but in some way they 

 are irritated and hand over 

 to nerve fibres connected with 

 them a message which is car- 

 ried to the brain; and this 

 message produces a sense of 

 smell. 



The olfactory area is too 



surface of the nasal passages, the rest of high in the nOS6 f Or the main 

 the cells and fibres being within the p 11rr ^ n f<3 rf air fn rkaaa niror 

 other soft tissues in the nose. (Schafer) 



it. Consequently, when one 



wishes to perceive very faint odors, the muscles of the nose 

 contract slightly, widening the passages, and one " sniffs" the 

 air. By this we mean that one draws in the air in short, 

 quick breaths, which dislodge the air already in the smelling 

 region, and fill it with a new supply. These movements of 

 the nose and the sniffing process are seen most plainly in 

 animals, like dogs or foxes, which use this sense in locating 

 food. 



Adenoid Growths. Adenoids are unusual growths just 

 back of the nasal canals, in the region where these open 

 into the pharynx. Occasionally they occur as far down 

 as the tonsils, in which case the tonsils, too, are generally in- 



Celb lining the I , , , , ir ,, rjL 



Nasal fcyeUUfcIl:JJB*-*Af ucou Cells 



Of factory Celt! 

 FIG. 97. THE NERVES AND CELLS 



CONNECTED WITH THE SENSE OF 



SMELL 



The olfactory and mucous cells are on the 



