CHAPTER IX 

 NUTRITION 



Nutrition is the earliest and most constant of vital 

 operations. So prominent is the nutritive apparatus, 

 that an animal has been likened to a moving sac, organ- 

 ized to convert foreign matter into its own likeness, to 

 which the complex organs of animal life are but auxil- 

 iaries. Thus, the bones and muscles are levers and cords 

 to carry the body about, while the nervous system directs 

 its motions in quest of food. 



The objects of nutrition are growth, repair, propaga- 

 tion, and supplying energy to perform the work, or 

 functions, of the body. The first object of life is to 

 grow, for no animal is born finished. Some animals, 

 like plants, grow as long as they live; but the ma- 

 jority soon attain a fixed size. In all animals, how- 

 ever, without exception, food is wanted for another 

 purpose than growth, namely, to repair the waste 

 which is constantly going on. For every exercise of 

 the muscles and nerves involves the death and decay 

 of those tissues, as shown by the excretions. The 

 amount of matter expelled from the body, and the 

 amount of nourishment needed to make good the loss, 

 increase with the activity of the animal. The supply 

 must equal the demand, in order to maintain the life of 

 the individual ; and as an animal can not make food, 

 it must seek it from without. Not only the muscles and 

 nerves are wasted by use, but every organ in the body ; 

 so that the whole structure needs constant renewal. An 



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