LUNG CAPACITY 



329 



Go'mplein'ental 



Air 



luO cit. in. 



great pressure that disease of these parts may restilt. Such 

 tight clothing is evidently a menace to the health of the 

 body and is to be deplored. 



It is especially important that the growing child should 

 have free play of the chest cavity, and in exercising the 

 increased demands of the muscles for oxygen can be met 

 only by allowing free play to the lungs and walls of the 

 chest cavity. 



Lung capacity. — The amount of air respired in a breath- 

 ing depends, of course, upon the 

 extent of chest enlargement, and 

 the size of the individual. In 

 ordinary breathing, the amount 

 of air respired by all individuals 

 represents only a small propor- 

 tion of the total capacity of the 

 lungs. Even in deep expira- 

 tions, the lungs are never en- 

 tirely emptied of air. The figures 

 for an average adult are as fol- 

 lows: 



After the fullest possible in- 

 spiration the lungs contain about 

 three hundred and thirty cubic 

 inches of air. After the fullest 

 possible expiration following such 

 an inspiration they still contain 

 one hundred cubic inches of air. 

 The difference, two hundred and thirty cubic inches of air, 

 represents the greatest possible amount of air that can 

 enter and leave the lungs in a single respiration. This is 

 called the vital capacity of the lungs. In quiet breathing 



Tidal Air 

 30 cu. in. 



Reserve 

 Air 

 100 Cii 



111. 



Fig. 153 — Lung capacity. 



