CHAPTER IX. 

 NUTRITION. 



The Wastes of the Body. A man takes into his body 

 daily several pounds of foods of various kinds, as meats, 

 bread, vegetables, and water, yet he grows no heavier; it is, 

 therefore, clear that his body must in every twenty-four 

 hours "return, on the average, to the outside world about as 

 great a weight of matter as it receives from it. Even in 

 childhood, while growth is taking place and the body be- 

 coming heavier, the gain is never nearly equal to the weight 

 of the foods swallowed. The materials given off daily from 

 the body to the external universe, and compensating more 

 or less accurately for the receipts from the outside world, 

 are its wastes, and are chiefly things which cannot be 

 burned. Much of the food taken in can be, and is, oxi- 

 dized to enable us to move and keep warm. When burned 

 it is of no further use to us, and would only clog up the 

 various organs, as the ashes and smoke of an engine would 

 soon put its fire out if they were allowed to accumulate in 

 the furnace. The chief wastes of the body are carbon di- 

 oxide gas, water, and a kind of ammonia called urea. 



Receptive and Excretory Organs. Those organs of the 

 body whose function it is to gather new material from 

 outside for its use are known as receptive organs. There 



What facts make it clear that a man must daily give off several 

 pounds weight of matter from his body? Does a child's increase in 

 weight equal the weight of the food it has eaten? What is meant by 

 the "wastes" of the body? How do most foods differ from wastes 

 in regard to oxidation? Why must wastes be removed from the body? 

 Name the chief wastes of the body. 



What is meant by the receptive organs? 



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