CHAPTER XXV 

 RESPIRATION 



Most of us know how the fires in our stoves and 

 heaters are affected by the amount of air that draws 

 through the fuel. Close the air draft and the fire 

 smoulders or dies; open it and flame and heat increase. 

 So necessary is the oxygen of the air that in great boiler 

 rooms of ships and factories where much power is re- 

 quired, air is forced through the fires under pressure to 

 bring about better combustion. 



So, in our wonderful complicated body machines, air 

 is necessary that the food fuel may generate enough heat 

 to warm us and enough energy for our other needs. This 

 air supply is so vital that we cannot stop it for any length 

 of time without serious danger. 



Our respiratory apparatus works like an automatic 

 machine to supply air and to remove waste gases. But 

 it should be used in the right way and the air supply should 

 be fresh. If we understand the workings of our respira- 

 tory system we will know better how to safeguard it to 

 protect and strengthen our health. 



Respiration is the life process, or function, by which energy is 

 made available to the body. It includes breathing and oxidation. 



In man, breathing is the process by which air is taken into the 

 lungs and carbon dioxide is exhaled from them. 



Oxidation is the process by which oxygen, taken from the air 

 in the lungs, is combined with digested food substances in the 

 cells of the body, thus releasing energy for the body's needs. In 

 this process the circulation of the blood plays an important part. 



The blood, in circulating through the lungs, absorbs oxygen 

 from the air, and in circulating through the walls of the stomach 

 and other digestive organs it absorbs digested food substances. 

 By means of capillaries, a network of minute tubes, the blood 

 carries both the oxygen and the food substances to all cells in 

 the body. Oxidation, or burning, of food substances goes on in 

 every cell. The wastes from this burning are gathered up and 



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