Yellow Milk.—A yellow tint occurs in ordinary milk and cream, particularly in certain breeding districts—in Normandy, for example, where the butter produced is greatly valued on account of this appearance. Pathological yellow milk is the result of the growth of B. synxanthus Schröter, which secretes a substance resembling rennet, curdles the milk, and finally dissolves the clot, at the same time producing the yellow colour.
Bitter Milk.—Milk which is of a normal character on being withdrawn from the udder may acquire a bitter taste some hours later. At rest, this milk produces a small quantity of yellowish, frothy cream. The organisms which produce the change have been studied in Germany, Switzerland, and Auvergne. We may mention Weizmann’s bacillus of bitter milk, Conn’s micrococcus of bitter milk, and Duclaux’s Tyrothrix geniculatus.
Medicated Milk.—Medicated milk may be divided into two kinds: Firstly, medicated milk proper, which differs from normal milk inasmuch as it contains a certain proportion of drugs, which, when swallowed by milch cows are partly eliminated through the udder. When taken by a young animal or child such milk has a distinct therapeutic effect, depending on the principles employed.
It does not appear, however, that up to the present any very great success has followed this system. It is possible to increase the richness of the milk in phosphates, but as regards mercurial or iodine preparations the failure has been complete.
Secondly, fermented milks, which in addition to their nutritive action are made more digestible.
Fermented milk is easily digested, and is better borne by the weakest stomachs.
In human practice the fermented forms of milk are two, viz., kephyr and koumiss.
Kephyr is prepared in Afghanistan and Persia from camel’s milk, but for some years past it has been made in England with cow’s milk. A certain quantity of cow’s milk is placed in a bottle and the ferment, consisting of kephyr grains, is added. The lactose is converted into carbonic acid and alcohol in consequence of the action of certain lactic microbes.
This milk after ingestion does not require to be coagulated and then digested before absorption, a fact which considerably diminishes peptic digestion.
Koumiss is a milk preparation resembling kephyr; it is made by the Kirghizes with mare’s milk according to the same principles, but the ferment employed gives more alcohol.