MILK AND ITS CARE. 169 



2. Casein a7id Albumen. — These constituents 

 vary less in {quantity than does butter fat. They 

 are very similar in composition, and serve the 

 same purposes as food, but differ widely in ap- 

 pearance. They differ from other parts of milk 

 by containing sulphur, nitrogen, and phos- 

 phorus. 



(i) Casein. — This constituent of milk may be 

 seen as the curd which forms when milk sours. 

 It is present in milk in a very finely divided con- 

 dition in combination with lime. When milk 

 sours, the acid unites with the lime, and the 

 casein then becomes insoluble, and appears as 

 the common curd of sour milk. 



When milk is used for butter-making, the 

 most of the casein remains in the skim-milk, 

 some goes into the buttermilk, and a small 

 amount into the butter, making upon the aver- 

 age I per cent, of the latter. 



Casein is an important part of cheese, com- 

 posing approximately one-third of common 

 cheese. 



{2) Albumen. — This substance, as found in 

 milk, is practically the same as the white of an 

 eo-cr. It differs from casein in being entirely in 

 solution, making about .5 per cent. When milk is 

 heated to i6o°F., or above, the albumen is coag- 

 ulated, and is seen as a tough scum on the sur- 

 face. 



When milk is used for butter-making, the 



