MILK, the fluid designed for the nou rishment of young animals, and which is secreted in particular organs by the fe males of the class Msmmalis, is a white opaque fluid, having a sweetish taste, and a specific gravity somewhat greater than that of water. When milk newly taken from the animal is allowed to remain at rest, it separates into two parts ; a thick white fluid, called cream, collects on the surface, and the thud beneath is more watery. The quantity of cream obtained from milk, and the time it requires to separate, vary ac cording to the nature of the milk, and the temperature of the atmosphere. When the milk is allowed to stand after the spontaneous separation of the cream, it suffers another change : it first be. comes acescent, and then coagulates. When the coagulum is pressed gently, a serous fluid is forced out, and the re mainder is the caseous part of milk, or pure cheese. Butter and cheese are ob tained artificially ; the former by the operation of churning, and the milk which remains after the butter has been separated, or, as it is called, the butter milk, has all the properties of milk from which the cream has been separated. Cheese is obtained by the addition of ren net to the milk, which is prepared by di gesting the inner coat of the stomach of young animals, especially that of the calf. The quality of the cheese depends upon the quantity of cream that remains in the milk. The best cheese is obtained by co agulating the milk at the temperature of 100°, and expressing the whey slowly and gradually, without breaking down the curd. Whey expressed from coagulated milk, if boiled, and the whole curd pre cipitated, becomes transparent and co lourless. By slow evaporation it depo sits crystals of sugar, with some muriatc of potash, mu/late of soda, and phos phate of lime. The liquid which re mains after the separation of the salts is converted, by cooling, into a gelatinous substance. If whey be kept, it becomes sour, by the formation of an acid, which is the lactic acid; and it is to this that the spontaneous coagulation of milk after it remains at rest is owing. Milk may, af ter it is sour, be fermented, and it wilt yield a vinous intoxicating liquor. This is practised by the Tartais on the milk of the mare. Milk is likewise susceptible of the acetous fermentation. The results of very minute experiments prove that the constituent parts which enter into the composition of milk, are Milk Muriate of soda Oil Muriate of potash Curd Phosphate of lime Gelatine Sulphur.
Sugar of milk The milk of different animals is found to be composed of nearly the same sub stances; but the proportions vary so much, as to give them very different properties.
We shall give a brief account of the analysis of the French chemists Deyeux and Parmentier.
1. Every kind of milk, when left at rest, produces cream on the surface ; but it is different in the milk of different ani mals. In that of the cow it is copious, thick and yellow. In women's milk the quantity is small, and it is white and more liquid. Goat's milk produces abundance, and it .is thicker and whiter than that from the cow. Ewe's milk produces as much as that of the cow, and of nearly the same colour. The cream from milk resembles women's. In mare's milk it is very fluid, and similar in colour and consistence to good cow's milk before the cream appears on the surface.
2. Butter obtained from thonilk of dif ferent animals is thus composed. That of the cow differs in colour ; but has always much consistency. That from women's milk is small in quantity, insipid, and of a pale yellow. The butter of asses' milk is always white, soft, and disposed to be rancid. That -from goat's milk is abun. dant, white, and soft. The butter from ewe's milk is yellow and soft : that from mare's has but little consistence, and is readily decomposed.
3. The caseous part of milk varies in different animals, That from the milk of the cow is bulky, and retains much se. rum. That from women's milk is small in quantity, has an unctuous feel, and bul a small portion of whey' The curd 01 asses' milk is similar to that of the wo men's, but not unctuous. Curd from tilt milk of the goat is abundant, of a firmer consistence than that of the cow, and re tains less whey. Curd from ewe's milk is fat and viscid : that from mare's milk ii very similar to what is obtained from wo men's milk.
4. The serum, or whey, constitutes a great proportion of the milk, and shews the following varieties. That from the milk of the cow has a greenish cast, a sweet taste, contains sugarof milk and neutral salts. The whey from women's milk has little colour ; but contains much saccharine matter. The whey of eases' milk is colourless, and contains less salts, and more sugar than that of the cow. Whey of the goat is yellowish, and con tains very little sugar and saline matter. The latter is muriate of lime. The whey of ewe's milk is always colourless, and contains the smallest quantity of sugar, and but a small portion of muriate and That of mare's milk has little co our, and contains a large pro portion of saccharine matter, and of saline substances.