CHAPTER II. 



COMPOSITION OF THE ANIMAL BODY— DIGESTION- 

 METABOLISM. 



I. Composition of the Anijial Body. 



Division III of the preceding chapter sets forth the yield and 

 composition of an acre of Indian corn, thereby showing the man- 

 ner in which the several nutrients of feeding stuffs are elaborated 

 by the plants of the farm. We will next consider the nature and 

 composition of the bodies of farm animals, which are built up and 

 nourished by plants. 



19. The animal body. — The unit of the animal body is the proto- 

 plasmic life-holding cell, which, associated with myriads of others 

 and modified in innumerable ways, makes up the body structure. 

 Both the cell envelop and its contents are of nitrogenous material 

 in most complex combination. 



In studying the higher animals we may regard their bodies as 

 consisting of a bony skeleton of mineral character 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 dis- 

 solving, assorting, distributing, and utilizing the nutritive matters 

 of the food and for conveying and disposing of the waste. Finally 

 there are the nerves, which control and direct all body actions. 



20. Composition of animal bodies. — To aid in a study of the com- 

 position of the bodies of farm animals we have the following in- 

 valuable data gathered by those greatest of agricultural students, 

 Lawes and Gilbert^ of the Rothamsted (England) Experiment Sta- 

 tion, whose classic investigations stand as models in agricultural re- 

 search. 



21. Mineral matter. — The first division of the table shows the 

 composition of the entire body (fasted weight) of the animal. Re- 

 ferring to the first column we learn that in each 100 lbs. of the body 

 of the fat calf there are 3.80 lbs. of mineral matter, or ash. That 

 is, if the body of the calf were burned, there would remain that 



' Jour. Roy. Agr. Soc. Eng., 1898 ; U. S. Dept. Agr., Office Expt. Sta., Bui. 22. 



