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 CHAPTER IV

Milk is first of all the food for the young,—until a certain age the only food, and a perfect food. It contains but little refuse or waste and is under favorable conditions almost wholly digestible.

NUTRIENTS

All foods contain certain groups of nutrients which may be classified according to various functions in nutrition and their chemical composition.

Protein.—The protein group of nutrients contains nitrogen and is necessary for building up the tissues of the body, the muscles and the tendons which also contain nitrogen. Only by this group can tissues wasted by constant wear and tear be rebuilt. Proteins are the flesh-forming group. To some degree the proteins or albuminoids are also active in producing fat in the body, but the other groups of nutrients, especially the fats, also contribute.

Fats and Carbohydrates.—Another important function of food is to produce and maintain the animal heat. The main sources of this necessity are the fats and the carbohydrates, so called because they consist of the element carbon combined with oxygen and hydrogen, the last two in the exact proportion in which they are combined in water. All of these three groups furnish the fuel, so to speak, for the body, but they