CHAPTER II 



THE ANIMAL BODY— DIGESTION— METABOLISM 



I. The Composition of the Animal Body 



Having studied the composition of plants and the manner in which 

 they grow, let us now study the composition of the bodies of farm 

 animals, which are nourished by plants. 



The animal body. — The bodies of the higher animals consist of a 

 bony skeleton, chiefly of mineral matter, surrounded by an elaborate 

 muscular system. Fatty tissue permeates the bones and muscles, filling 

 in and rounding out the body form, and around all is the enveloping 

 skin. Within the body cavity are the various special organs, such as 

 the heart, stomach, etc., designed for dissolving, distributing, and 

 utilizing the nutrients of the food and for disposing of the waste. 

 All these organs are nitrogenous or protein in nature, as are also a 

 part of the organic matter of the bones and a large portion of the 

 nerves, which control and direct all body activities. 



Therefore, one of the fundamental differences between plants and 

 animals is that in animals the walls of the body cells are made chiefly 

 of protein, while in plants the walls of the cells are composed of cellu- 

 lose, which is a carbohydrate. Furthermore, in plants starch, another 

 carbohydrate, is the chief form in which reserve food is stored. In 

 animals, on the other hand, nearly all the reserve food is stored in the 

 form of fat. Tho small amounts of glucose and glycogen, or animal 

 starch, perform important functions in the bodies of animals, as we 

 shall see later in this chapter, these carbohydrates at no time form an 

 appreciable part of the animal's weight. 



Composition of animals. — Over 60 years ago Lawes and Gilbert, 

 the famous English agricultural scientists, analyzed the entire bodies 

 of several farm animals — a task involving much labor. During recent 

 years similar studies have been made at certain of the American experi- 

 ment stations. The following table,^ which summarizes some of these 

 investigations, shows that the composition of the bodies of farm animals 

 varies greatly according to their age and degree of fatness: 



1 Data for cattle from Haecker, Proc. Amer. Soc. Anim. Prod., 1914, and for 

 sheep and swine from Lawes and Gilbert, Philosophical Transactions, 1859. 



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