200 COMPOSITION OF MILK. 



appear to float in the watery matter. On more minute 

 examination, these butter-globules are seen to be 

 enclosed in a thin film of caseous matter. They are so 

 minute that they filter through the finest paper. Milk 

 readily assimilates with water and other sweet and 

 unfermented liquids, though it weighs four per cent, 

 more than water. Cold condenses, heat liquefies it. 



The elements of which it is composed, not being 

 similar in character or specific gravity, undergo rapid 

 changes when at rest. The oily particles, being lighter 

 than the rest, soon begin to separate from them, and 

 rise to the surface in the form of a yellowish semi-liquid 

 cream, while the greater specific gravity of the serous 

 matter, or whey, carries it to the bottom. 



A high temperature very soon develops acidity, and 

 hastens the separation of the cheesy matter, or curd, 

 from the whey. And so the three principal elements 

 are easily distinguished. 



But the oily or butyraceous matter, in rising to the 

 surface, brings up along with it many cheesy particles, 

 which mechanically adhere to it, and give it more or 

 less of a white instead of a yellow color ; and many 

 watery or serous particles, which make it thinner, or 

 more liquid, than it otherwise would be. If it rose up 

 free from the adhesion of the other elements, it would 

 appear in the form of pure butter, and would not need 

 to undergo the process of churning to separate it from 

 other substances. The time may come when some 

 means will be devised, either mechanical or chemical, 

 to separate the butter particles from the rest instan- 

 taneously and completely, and thus avoid the often long 

 and tedious process of churning. 



The coagulation, or collecting together of the cheesy 

 particles, by which the curd becomes separated from 

 the whey, sometimes takes place so rapidly, from the 



