Skim milk may be advantageously used by the poorer classes. Its deficiency in fat may be made up, easily, by obtaining it from cheaper sources than whole milk.
Buttermilk.
Buttermilk is obtained from cream during its manufacture into butter. Its composition differs but little from that of skim milk. It contains less proteid and sugar and more fat.
It has a slightly acid taste, which makes it an agreeable beverage, and it is well borne by people of weak digestion.
It acts as a laxative.
Whey.
When milk is clotted by the action of rennet, wine, or an acid, and after standing a few minutes is strained through a double thickness of cheese cloth, the liquid obtained is known as whey. It is a slightly laxative fluid of small nutritive value.
Koumiss, Kefir, and Matzoon.
Koumiss, originally fermented mare's milk, was first made, hundreds of years ago, in the steppes of Russia and Southwestern Asia. A double fermentation takes place in its manufacture,—lactic and alcoholic. Lactic fermentation begins first, while alcoholic lasts longer. It is the purpose of the Koumiss maker to hinder lactic fermentation as far as possible. Koumiss is made in the United States from cow's milk, yeast being the ferment used.
The alcohol (C2H5OH) and carbon dioxid (CO2) formed during fermentation render the milk more easily digested and absorbed than in its natural state. It is consequently of great value in the sick-room, and is the one form in which milk seldom fails to be retained by the patient.
Kefir and Matzoon are fermented cow's milk, varying but little in composition from Koumiss. Koumiss and
