62 



PURE AIR 



and the consequent filling of the lungs with air is known 

 as an inspiration. After we have raised the ribs, we al- 

 low the muscles which pull them up to relax ; as the ribs 

 sink back and the diaphragm expands curving up into 

 the chest cavity, the chest cavity becomes smaller and 

 pushes the air from the lungs. This is an expiration. 



Distinction between breathing and cell respiration. 

 Most boys and girls think that breathing takes place in 



the lungs. This is 

 true, but we would 

 soon die if the oxygen 

 stopped there. As a 

 matter of fact the 

 lungs are simply or- 

 gans which serve to 

 pass oxygen over to 

 the blood and to take 

 carbon dioxide and 

 waste matter from it. 

 The real respiration 

 takes place in the cells of the body which do work for 

 us. If we work the muscle of the arm, then that muscle 

 in order to do its work must oxidize some fuel or food 

 material which has been carried to it by the blood. If 

 we work with the brain, then food must be oxidized in 

 the brain cells in order that energy may be released there. 

 The blood, like a railroad train, carries the oxygen from the 

 lungs to all places in the body where oxygen is needed. 

 In the blood are little cells known as red corpuscles. These 

 cells have the peculiar ability to carry oxygen. They are 

 also able to give up this oxygen where it is needed in the 

 body. Thus the blood becomes a medium of exchange 



The respiration of cells. 



