Average Composition Of Milk (Snyder)

Milk is the food of the young animal, and hence contains all the nutrients necessary for the support of the body. Owing to the large per cent of water in its composition, milk is a bulky food, and being deficient in starch, is not a satisfactory food for the healthy adult.

Milk is a white, opaque liquid. It consists of a bluish white liquid, called serum, in which float globules of fat, which give the milk the appearance of a white liquid. These fat globules are suspended through the milk in the form of an emulsion, fresh milk being the most perfect example of an emulsion. Upon standing, however, the emulsion is broken and the fat rises to the surface in the form of cream.

Butter is made by separating the fat from cream by churning, thus completely breaking down the emulsion of fat. Skimmed milk contains practically all the ingredients of whole milk with the exception of the fat, and forms a cheap supply of protein. The protein of the milk is largely in the form of casein, which contains both sulphur and phosphorus.

Casein coagulates when an acid is added to it, or when an acid is formed in the milk during the process of lactic fermentation. It forms a clot in the stomach by the action of the enzyme rennin, which is secreted by the stomach, and it then digests as a solid food. In cheese making and in the making of junket, a commercial form of rennin obtained from the second stomach of the calf is added to the milk, thus causing it to clot. The addition of limewater, or some cereal water, as barley water, tends to make the casein form a lighter and more digestible clot, hence they are often added to baby foods.

The albumen of milk, or lact-albumen, coagulates with heat and forms the scum of boiled milk.

Lactose, or milk sugar, is less soluble than cane sugar and does not taste as sweet. It is the sugar which is used in baby foods. It is obtained from the whey left from cheese making after the casein and fat have been removed.

The souring of milk is caused by the action of lactic bacilli present in the milk. The bacilli feed upon the lactose changing it to lactic acid, which acid reacts upon the casein, causing it to coagulate, or form a curd. In the large intestine of the human body are found great numbers of bacteria which feed upon the food residue present there, forming injurious compounds which are absorbed by the blood, with harmful results. The growth of some of these putrefactive bacteria is thought to be checked by the presence of lactic acid and by the action of lactic bacilli; hence, sour milk is considered a healthful, as well as a nutritious food.

The mineral matter in milk consists largely of the phosphates and chlorides of soda, lime, and potash.

Milk contains large numbers of bacteria. Few bacteria are normally present in fresh milk, but they enter the milk on account of the unsanitary conditions attendant upon milking and the subsequent care of milk. They reproduce very rapidly if the milk is not cooled. Typhoid fever, chil-dren's summer diseases of the intestines, tuberculosis, and other diseases are often traced to the milk supply; con-sequently, the most cleanly conditions should be insisted upon by the health authorities, in the stable, the care of the cow, cleanliness of the milkers and of all utensils which hold the milk. Milk should be sold only in bottles which are filled and sealed at the dairy, the seal to be broken by the consumer only.