Milk as a Food
Milk contains all the elements necessary in a balanced diet for the adult and furnishes an almost perfect food for the suckling. Milk is lacking in iron and roughage and is therefore not suitable for the sole diet of adults. This is compensated for in the infant by a large amount of iron which is contained in the spleen and furnishes this necessary element during the suckling period. There is no other single food that will so well promote the growth and development in young children. Milk is easily digested, is palatable, and forms one of our best and most important articles of food. It is asserted that the consumption of milk in the United States will average about 0.6 of a pint per capita per day. In many countries there is practically no milk used. In the United States about 16% of the dietary consists of milk and its products.
Milk is an animal secretion produced by the mammary gland and is exceedingly complex in its composition. It consists chiefly of water containing various solids in solution. Cow’s milk consists of 87% water and 13% solids. The solids consist of fats in emulsion, milk sugar, albumin, casein and mineral matter. Milk also contains such gases as oxygen, nitrogen and carbon dioxide. It contains enzymes, phosphatids and vitamins, also antibodies and other substances.
Fresh normal milk is an opaque fluid of white or yellowish-white color and has a sweetish taste and rather pleasant odor. In reaction milk is amphoteric, that is, it is acid to litmus and alkaline to turmeric. The specific gravity of cow’s milk is from 1.027 to 1.035. Under the microscope it is found to contain fat globules and cells, also bacteria and other objects. The oxygen and nitrogen that are found in milk are thought to be carried into it mechanically from the air during the process of milking. Lecithin, cholestrin, citric acid, lactosin, orotic acid and ammonia are found in milk in small quantities.