246 Life and Health 



front, while two other passages open into the pharynx 

 behind. 



To increase the area of the air passages the two light, 

 spongy turbinated bones, one on each side, form narrow, 

 winding channels. The mucous membrane, with the 

 branches of the olfactory nerve, lines the dividing wall 

 and the inner surfaces of these winding passages. 



381. The Sense of Smell. The sense of smell is excited 

 by the contact of odorous particles contained in the air 

 with the fibers of the olfactory nerves, which are distributed 

 over the delicate surface of the upper parts of the nasal 

 cavities. 



In ordinary quiet breathing, the air simply flows along the 

 lower nasal passages into the pharynx, scarcely entering the 

 olfactory chamber at all. This is the reason why, when we 

 wish to perceive a faint odor, we sniff up the air sharply. 



The delicacy of the sense of smell varies greatly in dif- 

 ferent individuals and in different animals. It is generally 

 more acute in savage races. Many animals are more highly 

 endowed with this sense than is man. The dog appears to 

 depend on the sense of smell almost as much as on sight. 

 Deer, wild horses, and antelopes probably surpass all other 

 animals in vividness of the sense of smell. 



382. Association of Smell and Taste. Smell has been 

 denned as "taste at a distance," and it is obvious that 

 these two senses not only form a natural group, but are 

 clearly associated in their physical action, especially in 

 connection with the perception of the flavor of food. The 

 sense of odor gives us information as to the quality of food 

 and drink, and more especially as to the quality of the air 

 we breathe. 



Taste is at the gateway of the alimentary canal, while 

 smell acts as the sentinel of the respiratory tract. Just as 



