166 RESPIRATION 



and without water for a considerable number of days, 

 because of storage within the body; but without air, 

 life is limited to minutes. 1 



Nose as an air passage. The mechanism for supply- 

 ing oxygen to the blood consists of two elastic bags or 

 reservoirs, the lungs, which lie within the chest walls and 

 are entered by way of the mouth and nose and the wind- 



meatus 



FIG. 97. Section through nose, showing how the turbinate bones are arranged to 

 increase the surface over which the air must pass. (Testut.) 



pipe, or trachea. So far as breathing is concerned, the 

 mouth and nose act mainly as canals through which the 

 air passes to the trachea. They are lined with a moist 

 membrane which catches the dust and thus helps to 

 prevent the entrance of irritating particles into the 

 lungs. This membrane also warms and moistens the air, 

 that irritation of the lungs by extreme cold and dryness 

 may be avoided. The nose is especially planned to serve 

 this purpose, in that it is provided with projections, the 

 turbinate bones, which divide the nasal passage into 

 several smaller passages and thus greatly increase the 



1 The longest recorded period of being under water with subse- 

 quent recovery is about fifteen minutes. 



