978 PRACTICE OF AGRICULTURE Part III. 



Sect. I. Of the Chemical Principles of Milk, and the Properties of the Milk of different 



Animals. 



6284. The milk used by the human species is obtained from various animals, but chiefly 

 the cow, ass, ewe, goat, mare, and camel ; that in most general use in British dairying is 

 the milk of the cow, which in modern times has received great improvement in quantity as 

 well as quality, by ameliorations in the form of milch cows, in their mode of nourishment, 

 and in the management of the dairy. Whatever be the kind of animal from which milk 

 is taken, its external character is that of a white opaque fluid, having a sweetish taste, and 

 a specific gravity somewhat greater than that of water. Newly taken from the animal, 

 and allowed to remain at rest, it separates into two parts ; a thick white fluid called cream, 

 which collects on the surface in a thin stratum ; and a more dense watery body, which re- 

 mains below. The quantity and quality of cream, and the time it requires to separate 

 from the milk, vary according to the nature of the milk and the temperature of the at- 

 mosphere. Milk which has stood some time after the separation of the cream first be- 

 comes acescent, and then coagulates. When the coagulum is pressed gently, a serous 

 fluid is forced out, and the remainder is the caseous part of milk, or pure cheese. 



6285. Butter, or soliditied cream, one of the most valuable products of milk, is obtained 

 artificially by churning ; an operation analogous in its effects to shaking or beating, by 

 which the cream separates from the caseous part and serum, in a more solid form tlian 

 when left to separate spontaneously. It is afterwards rendered still more solid by beat- 

 ing with a wooden spatula. 



6286. Cheese is obtained by first coagulating the milk, either with, or deprived of, its 

 cream, and then expressing the serum or whey ; the consolidated curd so produced forms 

 cheese. The milk may be coagulated in various ways, but that effect is chiefly produced 

 by the use of rennet, which is prepared by digesting the coat of young ruminating 

 animals, especially that of the calf. The rennet is poured into the milk when newly 

 brought from the cow, or the milk is warmed to 90" or 100" for that purpose. The 

 richness of cheese depends on the quantity of cream which the milk may have con- 

 tained ; its quality of keeping to the quantity of salt added ; and the degree of pressure 

 used to exclude the whey. 



6287. Whey expressed from coagulated milk, if boiled, and the whole curd precipi- 

 tated, becomes transparent and colorless. By slow evaporation it deposits crystals of 

 sugar, with some muriate of potash, muriate of soda, and phosphate of lime. The 

 liquid which remains 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 called the lactic acid ; and it is to this that the spontaneous coagulation of milk 

 after it remains at rest is owing. Milk may after it is sour be fermented, and it will 

 yield a vinous intoxicating liquor. This is practised by the inhabitants of the most 

 northerly islands of Europe, with butter-milk, and by the Tartars with the milk of the 

 mare. Milk is likewise susceptible of the acetous fermentation. 



6288. Tlie constituent parts of milk are found to be oil, curd, gelatine, sugar of milk, muriate of soda, 

 muriate of potash, phosphate of lime and sulphur. These substances enter into the milk of all animals, 

 but the proportions vary in different species. The various milks in use as food are thus distinguished. 



6289. Cow's milk produces a copious, thick, and yellow cream, from which a compact 

 consistent butter is formed ; the curd is bulky, and retains much serum, which has a 

 greenish hue, a sweet taste, and contains sugar of milk, and neutral salts. The milk of 

 the buffalo is essentially the same as that of the cow, 



6290. Ass^s milk throws up a cream resembling that of woman's milk ; the butter 

 made from it is white, soft, and disposed to be rancid ; the curd is similar to that of the 

 woman, but not unctuous ; the whey is colorless, and contains less salts, and more sugar^ 

 than that of the cow. 



6291. Eive'smilk throws up as much cream as that of the cow, and of nearly the 

 same color ; the butter made from it is yellow and soft ; the curd is fat and viscid ; the 

 whey is colorless, and contains the smallest quantity of sugar of any milk, and but a 

 small portion of muriate and phosphate of lime. 



6292. Goafs milk produces abundance of cream, which is thicker and whiter than 

 that from the covt^ ; the butter is white and soft, and equally copious, and so is the curd, 

 which is of a firmer consistence than that of the cow, and retains less whey. 



6293. Mare's milk produces a very fluid cream, similar in color and consistence to 

 good cow's milk before the cream appears on the surface ; the butter made from it has 

 but little consistence, and is readily decomposed. The curd is similar to that obtained 

 from woman's milk, and the whey has little color, and contains a large proportion of 

 saccharine matter, and of saline substances. 



6294. Camel's milk throws up little cream, which is whitish and thin, and affords an 

 insipid whitish butter ; the curd is small in quantity, and contains but little whey, which 

 is colorless and somewhat saccharine. 



