CHAPTER IX 

 BREATHING AND VENTILATION 



42. Breathing. From the chapter on Oxidation we 

 learned that a fire is kept burning by a continuous supply 

 of air which contains oxygen, and that the oxidation of 

 carbon compounds produces heat. Our bodies are kept 

 warm by oxidizing the food that we eat. The energy 

 necessary to move and to do work is produced in our 

 bodies by oxidation. In order to live, this oxidizing 

 process must never stop. It is the fire of life, and when 

 it stops life itself ceases. The body has two organs, the 

 lungs, whose work it is to get oxygen into the blood for 

 distribution to all parts of the body. 



Breathing, then, consists of the process of allowing 

 the air to flow into the lungs and forcing it out again. 

 By the action of the muscles of the chest and the dia- 

 phragm, the chest cavity containing the lungs is enlarged 

 and the air flows in because the pressure of the air on the 

 outside is greater than the pressure of the air in the lungs. 

 Air always flows to the place where the pressure is least. 

 When the lungs are full of air, the muscles of the chest 

 contract and force the air out. The air flows out because 

 the pressure in the lungs is then greater than the pressure 

 of the air on the outside. 



Lamps do not burn brightly or fires abundantly if the 

 supply of oxygen is for any cause insufficient. So it is 

 with our bodies. We shall not be bright and happy and 



