CHAPTEE VI 

 THE APPLIED PHYSIOLOGY OF EESPIEATION 



The Air Passages. 



THE nose is an organ whose function it is to protect the 

 lungs in the same way as the mouth protects the 

 stomach. It ' cooks ' the raw external air, if one may 

 use the expression, and renders it fit to enter the lungs. 

 It is enabled to do this by the tortuous course of its 

 airway, and by its succulent mucous membrane so 

 richly supplied with nerves, vessels, and glands. As the 

 air enters the nostrils, any large particles of foreign 

 matter which it contains are entangled by the vibrissse, 

 which like sentinels guard the entrance to the nasal 

 cavities. The current of air then sweeps upwards and 

 backwards in a curved direction to pass over the 

 superior and middle turbinated bodies. In its course it 

 is further purified from foreign particles by the layer of 

 viscid mucus which covers the lining membrane, and 

 which catches particles of dust and bacteria as a 

 fly-paper catches flies. At the same time the air is 

 moistened and warmed. It is moistened by the evapora- 

 tion of the watery secretion produced by the glands 

 embedded in the mucous membrane, and it has been 

 calculated that the nose yields up to the inspired air in 



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