RESPIRATION AND ENERGY IN MAN 



133 



and the lungs. Less efficient arrangements for this purpose 

 are found in the mouth cavity. Hence, if one breathes 

 through the mouth, one is likely to take in considerable 

 quantities of dust and bac- 

 teria, which may, in time, 

 cause inflammation or 

 other forms of disease. 



192. Effect of exercise 

 on respiration. Not only 

 does the heart beat more 

 rapidly during exercise, but 

 the rate of breathing also 

 increases. Oxygen is thus 

 supplied to the cells in 

 larger quantities, and more 

 wastes are eliminated. 

 Deep breathing is a prime 

 requisite for healthful liv- 

 ing, since in this way the 

 air is changed throughout 

 the lungs. In short, quick 

 breathing, on the other 

 hand, it is only the air in 



the upper regions of the lungs that is thus affected. The 

 " second wind " that the runner gets after a short time is 

 due to the expansion of all portions of the lung tissue. In 

 order to keep the chest walls flexible and capable of full en- 

 largement, a certain amount of regular exercise should be 

 persisted in throughout life. 



193. Effect of tight clothing upon respiration. In an 

 earlier part of this chapter we learned that air is forced into 

 the lungs when the front ends of the ribs are elevated and the 



A = inspiration. 



B = expiration. 



FIG. 42. Diagram to show changes in 

 the size of the chest cavity during in- 

 spiration and expiration. 



Ab = abdominal wall. 

 D = diaphragm. 

 St breastbone. 

 Tr = windpipe. 



