70 BODILY MOTION. 



inches = 3480 cubic centimeters. A woman 5 feet 5 inches 

 in height and of average girth, has a vital capacity of 

 not more than 160 cubic inches. From observations 

 made on a large number of male adults of ordinary 

 heights, it has been found that on the whole the vital 

 capacity varies according to the height of the individual, 

 in such a way that a difference of I inch in height 

 makes a difference of 150 centimeters, i.e. about 9 

 cubic inches in vital capacity ; and further, that be- 

 tween two men of the same height, but different girth, 

 there will be a difference of about the same amount, 

 viz., 9 cubic inches for every inch difference in girth. 

 Similar laws have been found to hold good as regards 

 female adults. In individual instances this result is 

 much affected by the flexibility of the chest, the mus- 

 cularity of the individual, and other circumstances, the 

 influence of which it is difficult to estimate. After the 

 most complete expiration possible, a quantity of air re- 

 mains in the thorax, which is sometimes called " residual," 

 and amounts to about 90 cubic inches. In the equilibrium 

 position the chest contains about 190 cubic inches ; when 

 fully expanded, about 300, of which 210 can be expelled. 



Two sounds are heard in listening to the normal chest, 

 viz., the vesicular inspiration sound, and the bronchial 

 sound, which is chiefly expiratory. The former has its 

 seat in the infundibula, the latter in the rima glottidis. In 

 each case the production of the sound is dependent on the 

 sudden widening of the channel along which the air flows. 



BODILY MOTION. 



Action of Voluntary Muscles on the Skeleton. With the 

 exception of those cases in which voluntary muscles act 

 peristaltically, the effect of muscular contraction in produc- 

 ing motions of the whole body, or of parts of it, is always 



