CHAPTER III 



FOOD AND DIGESTION 



Digestion is the process by which physical and chem- 

 ical alterations of foodstuffs, which fit them for absorp- 

 tion, are effected. Animal and vegetable tissues contain 

 foodstuffs of the same chemical composition; but some 

 animals can not convert certain forms of vegetable mat- 

 ter into food, while others can. When an animal feeds 

 upon other animals it is called carnivorous and feeds 

 upon tissues similar to its own. When it feeds upon 

 vegetables it is called herbivorous and feeds upon tis- 

 sues containing the same chemical elements but so ar- 

 ranged as to be not easily digested by carnivorous ani- 

 mals. With the aid of light, heat and moisture, vege- 

 tables take up chemical elements from air and soil and 

 combine them into the proper constituents of food for 

 herbivorous animals, and these in turn, convert them into 

 the similar, but more digestible foodstuffs required by 

 man. 



Of the elements of the chemist, only about twenty en- 

 ter into the composition of our tissues ; and of these, five 

 form so much of our bulk that the others may be men- 

 tioned as traces. The elements which chiefly concern us 

 occur as follows, in every hundred parts : 



Carbon, 53 



Oxygen, 22 



Nitrogen, 16 



Hydrogen, 7 



Sulphur, 2 

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