366 



ELEMENTARY PHYSIOLOGY 



The accessory part of the organ of smell may be 

 described as follows : — 



From the arrangements which have been described, it 

 is clear that, under ordinary 

 circumstances, the gentle in- 

 spiratory and expiratory cur- 

 rents will flow along the 

 comparatively wide, direct 

 passages afforded by so much 

 of the nasal chamber as lies 

 below the middle turbinal ; 

 and that they will hardly 

 move the air enclosed in the 

 narrow interspace between 

 the septum and the upper 

 and middle spongy bones, 

 which is the proper olfactory 

 chamber. 



If the air currents are laden 

 with particles of odorous 

 matter, these can only reach 

 the olfactory membrane by 

 diffusing themselves into this 

 narrow interspace ; and, if 

 there be but few of these par- 

 ticles, they will run the risk 

 of not reaching the olfactory 

 mucous membrane at all, 

 unless the air in contact with 

 it be exchanged for some of 

 the odoriferous air. Hence 

 it is that, Avhen we wish to 

 perceive a faint odour more 

 distinctly, we "sniff" or 

 snuff up the air. Each sniff is a sudden inspiration, the 

 effect of which must reach the air in tlie olfactory chamber 

 at the same time as, or even before, it affects that at the 



Fio. 117.— Cells of Olfactory 

 Epithelium. (Max Scbultze.) 



1, From a frog ; 2, from man. 



a, columnar epithelial cell ; 

 ft, olfactory rod-cell ; c, outer 

 limb, d, inner limb of olfactory 

 cell, the former being proloiigod 

 at e into fine hairs, the latter 

 being continuous with a nerve 

 filament from the olfactory 

 nerve. 



