MILK, BUTTER, CHEESE AND EGGS.CHAPTER XLI.
General Observations on Milk, Butter, Cheese, and Eggs, their Nutritious Properties, and Distinguishing Features, etc.
Milk is obtained only from the Mammalia, and is intended by nature for the nourishment of their young. All young animals live upon it for the first months of their existence, and it is the only food that, taken alone, can support adult life. The fat rises in the form of cream; curd is the nitrogenous matter; and the whey contains sugar and milk lactose with saline or mineral matter. For the majority of those who lead healthy, simple lives, milk is an excellent article of diet, but the milk of each animal is distinguished by some peculiarities; and as that of the cow is by far the most useful to us, the following remarks will chiefly have reference to that source of supply. When drawn from the cow, the milk is of a yellowish-white colour, and is most yellow at the beginning of the period of lactation. Its taste is agreeable, and rather saccharine. The specific gravity of milk is somewhat greater than that of water, but varies somewhat in the milk produced from different individuals. On an, the specific gravity of milk is 1.032, water being 1.
Milk, as it is drawn from the cow, is slightly alkaline, but afterwards lactic acid is formed, so that it becomes at first neutral, then acid, and the acidity goes on increasing until it is easily perceptible to the taste. This acidity is said to assist in the rising of the cream. Most schemes for preserving milk fresh consist in the addition of some alkali to correct this acidity. A pinch of bi-carbonate of soda is efficacious, and with it decidedly sour milk can often be boiled without curdling, but it gives an unpleasant flavour. Preparations are sold of which the principal constituent is boracic acid, and it is said that most of the milk that comes to London is treated in this way.