CHAPTER V 



RESPIRATION 



43. Review. We have learned what the cells of 

 the human body consist of, and what they need in order 

 to do their work well and to keep us in good health. We 

 have learned which foods are most nutritious and what 

 substances are harmful. We have also learned what 

 we should drink to keep in perfect health. The foods 

 we eat and the liquids we drink can be used by the cells 

 of the body only when there is a large amount of fresh 

 air (oxygen) in the cells. The oxygen of the air com- 

 bines with the foods, causing a very slow burning or 

 oxidation to take place in the cells. 



We must now learn how the air gets from the room 

 in which we live into each and every cell of the body, 

 where it is used. That whole process we call respi- 

 ration. 



44. The Air Passages. We breathe through the 

 skin as some of the lower animals do, but most of the 

 air gets into the blood through a number of tubes that 

 together are called the air passages. Air enters the 

 body through the nose, which is the beginning of these 

 air tubes. Then follow the pharynx, larynx, trachea 

 (windpipe), two bronchi, many bronchial tubes, and, 



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