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MANUAL OF PHYSIOLOGY. 



tremities of these rod-shaped filaments expand to surround a nu- 

 cleus, and are then continued into a network of filaments, into 

 which prolongations of the epithelial cells also seem to pass, and 

 in which the delicate fibrils of the olfactory nerve can be traced. 

 The existence of direct communication between the nerves and 

 the rod-shaped filaments and the epithelial cells is satisfactorily 

 established. 



The odorous particles must be in the form of gases, in order to 

 be carried by the air into the olfactory region, and the air must 

 be kept in motion, by sniffing it in and out of the nasal cavity, in 



FIG. 214. 



Section through tho mucous membrane of the nusal lassu in the level of 

 the olfactive region. a, Epithelial cells and bundles of nerves ; 6, Glands 

 separated from each other by bundles of nerves, c. (Cadiat.) 



order to excite the nerve terminals, which are not influenced by 

 the odors of air absolutely at rest, though it be in contact with 

 the mucous membrane of the olfactory tract. 



The extreme delicacy of appreciation of odors by the olfactory 

 nerve terminals is very remarkable. Even in human beings, 

 whose sense of smell is but poorly developed when compared with 

 that of animals, an amount of odorous substance can be perceived 



