222 



STUDIES IN PHYSIOLOGY 



from purple to scarlet, undergone by the blood in the pul- 

 monary capillaries, is due, as we proved on p. 121, to the 

 absorption of oxygen. The various exchanges that take 

 place between blood and air in the air sacs of the lungs may 

 be stated in tabular form as follows : 



4. HYGIENE OF THE RESPIRATORY ORGANS 



Hygienic Habits of Breathing. We have called attention 

 (p. 211), to the admirable provisions in the nose for filtering 

 and warming the air. No such arrangements are provided 

 in the mouth cavity. Hence, if one breathes through the 

 mouth, one is likely to take in considerable quantities of dust 

 and bacteria, and these, in the long run are likely to cause 

 inflammation or other form of disease. Catarrh is an acute 

 inflammation of the mucous membranes of the throat and 

 nose, and it sometimes becomes so bad that these air pas- 

 sages are more or less closed. If one has this trouble with 

 breathing, one should at once consult a physician. 



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 in larger quanti- 

 ties, and more wastes are eliminated. .Deep breathing is a 

 prime requisite for healthful living, 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 

 pulmonary regions which 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 



