THE THORAX AS A BELLOWS 



147 



It thus appears that the thorax, the lungs, and the 

 trachea constitute a sort of bellows without a valve, in 

 which the thorax and the lungs represent the body of the 

 bellows, while the trachea is the pipe ; and the effect of 

 the respiratory naovements is just the same as that of 



Fig. 48. — Diagrammatic Sections of the Body in 



A, inspiration ; £, expiration ; Tr, trachea ; St, sternum ; D, diaphragm ; 

 Ab, abdominal walls. The shading roughly indicates the stationary air. 



the approximation and separation of the handles of the 

 bellows, which drive out and draw in the aii' through the 

 pipe. There is, however, one difference between the 

 bellows and the respiratory apparatus, of great importance 

 in the theory of respiration, though frequently overlooked ; 

 and that is, that the sides of the bellows can be brought 



L 2 



