PRINCIPLES OF VENTILATION 



315 



* 



COMPLEMENTAL AIR. 



120 cu. in. 



Air that can be, but seldom is, 

 taken in. 



TIDAL AIR. 20 to 30 cu. in. 



Taken in and sent out at each breath 



RESERVE AIR. 

 100 cu. in. 



Air that can be, but seldom is, 

 driven out. 



RESIDUAL AIR. 

 100 cu. in. 



Air that can not be driven 

 out. 



o3 



.^ CO 



O '-' 



<M 



Is 



is 



Diagram Illustrating Lung Capacity 



From this diagram, we see that the average amount of air 

 in the lungs is 210 to 215 cu. in., while the tidal air is only 20 to 

 30 cu. in. Now, as already stated, it is known that exhaled tidal 

 air contains about 4 per cent, carbon dioxide. It must be re- 

 membered that the exhaled tidal air is the very purest air in 

 the lungs. The 100 cu. in. of RESERVE AIR is somewhat mixed 

 with the 30 cu. in. of tidal air and therefore diluted by it. 

 But the 100 cu. in. of RESIDUAL AIR, being the air in the 



