MECHANISM AND CHEMISTRY OF RESPIRATION 197 



Complemental Air 



lOOCu. in. 



Air that can be taken 

 in with a deep breath 



Tidal Air 3OCu in _ 

 Taken in with each breath. 



THE CAPACITY OF THE LUNGS 



With each inspiration, a certain amount of air is drawn 

 into the lungs and with each expiration it is forced out. The 

 lungs, however, are never completely emptied in expiration 

 and never filled in an ordinary inspiration. At each inspira- 

 tion, the average person takes into his lungs about 30 

 cubic inches of new air. This is called the tidal air. With 

 some effort, about 100 cubic inches 

 of complemental air can be inhaled and 

 exhaled in addition to the tidal air. 

 After an expiration of the tidal air, one 

 can, by effort, expel an additional 100 

 cubic inches of so-called supplemental 

 air. Even after the greatest effort 

 of expiration there remain in the lungs 

 about 60 cubic inches of residual air 

 which cannot be expelled; Fig. 104. 

 These figures are only the average, and 

 different individuals have very differ- 

 ent breathing habits, i.e. some, even in 

 quiet breathing, inspire three times as 

 much air as others. 



Thus with an ordinary breath only 

 about 30 cubic inches of the 190 

 cubic inches of air in the lungs of the 

 normal individual is changed. The 

 larger bronchi can hold 10 cubic 

 inches of air without much difficulty 

 and, therefore, much of the air 

 breathed in and out is merely used in ventilating these tubes. 

 Hence the air in the deepest parts of the lungs that in 

 the alveoli, or air sacs is not wholly changed. The lungs, 

 therefore, are never entirely filled with fresh air. The only 

 way that fresh air usually gets into the air sacs, where it 



Supplemental Air 



100 Cu. in 



Air that can be expelled 

 with a deep expiration 



Residual Air 



60 Cu. in. 



Air that cannot be 

 driven from the lungs 



FIG. 104. DIAGRAM 



Showing relative amount 

 of air in lungs under dn- 

 ferent circumstances. 



