CHAPTER XLIII 

 EXCRETORY SYSTEM 



General. A furnace must not only be supplied with 

 fuel and air, but from it must constantly be removed 

 smoke and ashes. Every boy, at least, appreciates the 

 amount of ashes formed and the importance of their 

 removal. 



We already know how our bodies are supplied with 

 food and oxygen. We also know that in the process of 

 living, parts of the body are constantly being oxidized 

 and other parts are being worn out. As a result of 

 these destructive processes, tcaste products are formed. 

 Chief among these are carbon dioxide, water, and urea. 



The organs used in- the elimination of these Avastes 

 are the lungs, the skin, the kidneys, and to some extent, 

 the liver. These are known as excretory organs. Which 

 of the waste products are removed by the lungs? 



The kidneys. The kidneys are organs through which 

 urea (nitrogenous waste) and water are removed from 

 the blood. In addition to these the kidneys excrete 

 some carbon dioxide, salts, and small quantities of other 

 substances. On each side of the backbone in the 

 abdominal cavity lie two bodies about five inches long. 

 These are the kidneys. In the figure notice the shape 



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