RATE OF BREATHING 



181 



larger. The lungs, which he within this cavity, are filled by the 

 air rushing into the larger space thus made. An expiration is 

 simpler than an inspiration, for it requires no muscular effort ; 

 the muscles relax, the breastbone and ribs sink into place, while 

 the diaphragm retiu'ns to its 

 original position and the air is 

 pushed out. 



Rate of Breathing and Amount 

 of Air Breathed. — During quiet 

 breathing, the rate of inspiration is 

 from fifteen to eighteen times per 

 minute; this rate largely depends 

 on the amount of physical work 

 performed. About 30 cubic inches 

 of air are taken in and expelled 

 during the ordinary quiet respira- 

 tion. The air so breathed is called 

 tidal air. In a " long " breath, we 

 take in about 100 cubic inches in 

 addition to the tidal air. This is 

 called complemental air. By means 

 of a forced expiration, it is possible 



to expel from 75 to 100 cubic inches more than tidal aii-; this air is called 

 reserve air. What remains in the lungs, amounting to 100 cubic inches, is 

 called the residual air. The value of deep breathing is seen by a glance at the 

 diagram, for when we take a deep breath we ventilate the lungs and exercise 

 the deeper-placed air sacs. 



Hygienic Habits of Breathing. — Every one ought to accustom 

 himself upon going into the open air to inspire slowly and deeply 

 to the full capacity of the lungs. A slow expiration should follow. 

 Take care to force the air out. Breathe through the nose, thus 

 warming the inspired air before it enters the lungs. Repeat this 

 exercise several times every day. You will thus prevent certain 

 of the air sacs which otherwise are not often used from becoming 

 hardened and permanently closed. 



Deep breathing should become a habit with growing girls and 

 boys. It can best be practiced in your bedroom, with windows 

 open, after rising in the morning and just before retiring at night. 



Common Diseases of the Nose and Throat. — Catarrh is a dis- 

 ease to which people with sensitive nmcous membrane of the nose 



H. NEW CIV. BIOL. — 13 



Diagram showing the relative amounts 

 of tidal, complemental, reserve, and resid- 

 ual air in the lung capacity of an adult man. 



