COMMON DISEASES OF THE NOSE AND THROAT 407 



cavity for the air to rush in. Then the diaphragm relaxes and 

 rises and the muscles between the ribs relax. This pressure forces 

 the air out of the lungs, thus producing expiration. During these 

 processes an exchange of oxygen in the air and of carbon dioxide 

 in the blood takes place. 



Practical Exercise 6. Explain the difference between breathing and respi- 

 ration. 



Hygienic habits of breathing. Every one ought to accustom 

 himself to inspire slowly and deeply in the open air. A slow 

 expiration should follow. Take care to force all the air out. 

 Breathe through the 

 nose to warm the in- 

 spired air before it 

 enters the lungs. Re- 

 peat this exercise 

 several times every 

 day. This will prevent 

 certain of the air sacs, 

 otherwise used only in- 

 frequently, from be- 

 coming hardened and 

 permanently closed. 

 Deep breathing should 

 become a habit with 

 growing girls and 

 boys. It can best be 

 practiced with win- 

 dows open, after rising 

 in the morning 

 just before retiring at 

 night. 



Common diseases of the nose and throat. Catarrh is a dis- 

 ease to which many people with sensitive mucous membrane of 

 the nose and throat are subject. It is indicated by the constant 

 secretion of mucus from this membrane. Chronic catarrh should 

 be attended to by a physician. Often we find children breathing 

 entirely through the mouth because the air passages in the nose 



^KJcu.in., 



Diagram showing the capacity of the lungs. The tidal air 

 is that taken in an ordinary breath. Complemental air is 

 and that taken in a very long breath. In a forced expiration we 

 can expel from 75 to 100 cubic inches of reserve air. What 

 is left in the lungs is residual air. 



