284 



PHYSIOLOGICAL PHYSICS. [Chap. xxm. 



respiration accomplished, when again equilibrium is 

 restored, only, however, to be again disturbed, after a 

 short pause, by a re-enlargement of the chest cavity, 

 and a repetition of the old process. 



Though the phrase chest cavity is used, it must be 

 noted that there is no actual space between the chest 

 walls and their contained organs. The lungs distend 

 pari passu with the enlargement of the chest, and 

 consequently a space is not actually produced. 



The distension of the lungs, then, producing inspi- 

 ration is simply due to diminution of pressure in the 

 chamber in which they are suspended. Reference to 

 page 270 will show that rarefaction of the air in a 

 receiver will cause a bladder contained in it, and 

 partially filled with air, to become expanded by the 

 elastic force of the air it contains. Much more will 

 such distension occur when the bladder is not shut 

 off from the outer air. Fig. 125 shows how the pro- 

 cess of inspiration and 

 expiration may be me- 

 chanically simulated. 



It represents a 

 glass flask with a 

 bottom of leather 4 

 movable by a knob 

 5. The wide mouth 

 of the flask is closed 



Fig. 125. The Mechanism of luspira- by ail air-tight-fitting 



Expirat cork, through which 



passes a glass tube. The tube divides into two 

 branches, the extremity of each having attached to it 

 an indiarubber ba^. The ba}s have 110 communication 



O O 



with the air in the flask, but communicate with the 

 air outside by means of the tube. At one side of the 

 flask is a mercury manometer 3 open to the air in 

 the flask. At the other side a small portion of the 

 wall 6 is formed of indiarubber. In the position 



