Page:Food and cookery for the sick and convalescent.djvu/84

52 The pathogenic germs in milk are often causes of typhoid fever, diphtheria, scarlet fever, tuberculosis, and cholera. They are killed at 167° F., a much lower temperature than the micro-organisms which produce souring, and they also occur in smaller numbers.

When in doubt of the milk supply, it is always best to scald it.

If milk is allowed to stand for a few hours, the fat rises to the surface in the form of cream; this is due to its lower specific gravity. Such cream is called gravity cream. When a separator is used for removing cream, the cream thus obtained is called centrifugal cream. It must not be inferred from this that cream contains nothing but fat, for it holds relatively as large a proportion of sugar and proteid as milk itself, the deficiency being in the proportion of water. Cream is an expensive form of fat, and must be regarded as a luxury.

Lactose (sugar of milk) is equal in nutritive value to cane sugar. It has some advantages over cane sugar, for under ordinary conditions it does not ferment, it is not so quickly absorbed, and it is a diuretic. Lactose is not so sweet to the taste as cane sugar, which renders it of value in the sick-room; it is, however, an expensive fuel food.

The proteid of milk is the cheapest form in which animal proteid may be obtained. It consists principally of casein, albumen to a smaller extent, some globulin, and traces of peptone.

Potassium, sodium, calcium, magnesium, iron, sulphur, phosphorus, and chlorine are all found in the ash of milk in the form of oxides, chlorides, or acids.

Milk from which most of the fat has been removed is known as skim milk. The quantity of fat removed depends on the manner in which the work is accomplished. Separator skimmed milk has less fat than that from deep cold setting. Skim milk has more proteid than whole milk, and a slightly larger proportion of milk sugar.