CHAPTER XVII 

 ANIMAL NUTRITION 



116. Purposes of Animal Food. Food serves the animal 

 in three ways. 



1. To act as a fuel to keep up the temperature above 

 that of the surrounding air. This is accomplished by the 

 oxidation of the combustible portion of the food through- 

 out the body in the capillaries wherein the oxygen in the 

 blood corpuscles comes in contact with combustible matter 

 in the blood serum. 



2. To furnish energy by which the mechanical or mental 

 work of the body may be produced. 



3. To build up or keep in repair the bodily structures. 



117. Classes of Foods. Plants can sustain themselves 

 upon very simple foods such as water, carbon dioxide and 

 mineral salts, while animals are so constructed that they de- 

 mand more highly organized foods and are therefore depen- 

 dent upon plant structures or upon animals that subsist 

 upon vegetable food. 



Foods of animals fall into one of four classes: 



1. Proteins. These are composed of carbon, hydrogen 

 and oxygen with a rather large amount of nitrogen (16 per 

 cent) and generally small portions of sulphur and iron. The 

 amount of protein is calculated by multiplying the nitrogen 

 content of the material by the factor 6.25. Proteins are 

 utilized by animals to build up worn-out muscular tissue. 

 They are found in the gluten of flour, beans, nuts and 

 generally in the seeds of plants, in lean meat, milk, cheese 

 and whites of eggs, as well as in various feeds. 



2. Carbohydrates. These are made up of carbon, hydro- 

 gen and oxygen, the two latter in the same proportion as 



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