CHAPTER XII 



THE SKIN AND THE KIDNEYS 



113. Review. We have traced the foods from the 

 time they entered the mouth through the many changes 

 of digestion, absorption, circulation, and oxidation in 

 the cells, until they were finally changed into useless 

 substances. They have served their purpose. The re- 

 moval of the wastes from the body is just as important 

 to health as the taking of nutritious foods. A large 

 city has trains and boats bringing food to supply its 

 inhabitants, but equally important and often more diffi- 

 cult to solve is the problem of how to get rid of the 

 garbage and sewage. 



In the body we find certain organs whose chief busi- 

 ness it is to remove the wastes from the blood and to 

 eliminate them from the body. The lungs, intestines, 

 skin, and kidneys together keep these useless and harm- 

 ful products from accumulating in the blood. They are 

 the organs of excretion. We have learned that the 

 lungs remove carbon dioxid, and the large intestine 

 removes certain indigestible parts of the foods and 

 wastes poured into the alimentary canal. We shall now 

 study the skin and the kidneys to see what part they 

 play in removing the wastes from the body. 



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