CHAPTER XXXVIII 

 THE VENTILATING SYSTEM OF THE BODY 



227. Respiration. In the animal or plant body, energy is 

 secured by oxidizing the food, that is, by combining the oxygen 

 of the air with the carbon contained in the food (103, 105). 

 Much of the energy used in our factories is derived in essen- 

 tially the same way by combining oxygen with the carbon 

 in coal. The oxidation of the food in living things takes place 

 in the cells, and the process is quite different from breathing 

 which is properly Only the inspiration and expiration of the 

 air by the lungs. All living things respire, but many cannot 

 strictly be said to breathe since they have neither lungs nor 

 other organs for the purpose. In the simplest animals, indeed, 

 each cell obtains the necessary oxygen for respiration from its 

 immediate surroundings, but, in animal bodies consisting of a 

 multitude of cells, means must be found for getting oxygen 

 to the more distant ones whose situation prevents their ob- 

 taining it for themselves. Thus have arisen gills, trachea, 

 lungs, and a circulatory system. 



228. Organs of Breathing. The nose, throat, trachea or 

 windpipe, the bronchial tubes, and the lungs are the organs of 

 breathing in man. The transfer of gases between the blood 

 and the air goes on only in the lungs, and the other organs 

 of breathing, therefore, serve chiefly to form a passageway 

 between the lungs and the surface o f the body. The air passes 

 through the nose into the throat and is thereby warmed, 

 moistened, and, to a large extent, freed from any dust it may 

 contain. From the throat the air enters the trachea. This 

 is a short tube kept open by Oshaped rings of cartilage. 



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