386 



BIOLOGY FOR BEGINNERS 



Air Capacity. The total capacity of the lungs is about 350 cubic 

 inches of which our ordinary breathing utilizes but about 30. By 

 extra effort we can take in and force out an extra hundred or more, 

 while there is about another hundred cubic inches which we can- 

 not get out at any one breath. When we realize the great import- 

 ance of oxygen to the tissues these facts ought to be an argument 

 for fresh air, deep breathing, and loose clothing. We use little 

 RESP.RAT.OH CHART. enough of our lungs, at 



best, so every effort ought 



, to be made to increase 



their activity. The one- 

 third of the air which can- 

 not be forced out of the 

 lungs provides for continu- 

 ous osmosis. Breathing is 

 an intermittent process but 

 the blood's supply of air 

 has to be continuous, 

 hence the need for some 

 air always in the lungs. 

 A reason for deep breath- 



(30 





FIG. 124. Compare capacity utilized by 

 ordinary breathing with that of deep 

 breathing. 



ing is to mix as much 

 fresh air with this " resi- 

 dual air " as is possible 

 at each breath. 



Breathing Movements; The process of getting air into and 

 out from the lungs is rather complicated and consists of two sets 

 of operations, inspiration (breathing in) and expiration (breath- 

 ing out) which we somewhat wrongly call the acts of respira- 

 tion. 



Inspiration: The Diaphragm. The chief breathing organ is the 

 diaphragm, a muscle (not a mere partition) which extends across 

 the body, curving upward, as a floor to the lung cavity. When 

 its muscles contract it tends to pull down straighter across the body, 

 thus giving the lungs more room, but compressing the abdominal 

 organs beneath it at the same time. 



