54 



HUMAN PHYSIOLOGY 



CHAP. 



53. Changes in the Air. The air we inhale is a mix- 

 ture of oxygen, nitrogen, carbon dioxid, argon, and more 

 or less moisture. As it comes from the lungs the same 

 things are found in it, but their proportion has been very 

 much changed, as is shown by the following table : 



1. The air has lost oxygen. The cells all over the 

 body consume oxygen in performing their various func- 

 tions. Oxygen is a very important element that easily 

 combines with many substances. 



2. The air has gained a large amount of carbon 

 dioxid. When the foods are oxidized in the cells to 

 furnish heat and energy, a large quantity of carbon 

 dioxid is formed, which is a waste and must be removed 

 from the blood. There seems to be an exchange in the 

 lungs, oxygen going into the blood and carbon dioxid 

 leaving it. 



3. Good fresh air is quite free from organic impuri- 

 ties. In the body a large amount of these wastes is con- 

 stantly made and poured into the blood. These wastes 

 are removed in part through the lungs. The character- 

 istic odor of exhaled air is due to this decaying animal 

 matter. 



4. The amount of watery vapor in the inhaled air 

 varies from time to time, depending upon the amount of 



