170 DAIRY FARMING 



of the cow, (4) interval between milkings, (5) portion of 

 the milking, fore milk or strippings. 



As food, fat serves as fuel to supply heat for the body, and 

 energy to keep up the body functions. The surplus is stored 

 as body fat, which serves as a storehouse of reserve material 

 for future use. Fat does not make growth of bone or muscle. 



156. Protein. The protein varies in amount from 2.5 to 

 4.2 per cent in extreme cases. Mixed milk usually varies 

 between 3 and 3.5 per cent. Protein contains nitrogen 

 combined with hydrogen, carbon, and small quantities of 

 phosphorus and sulphur. The proteins in milk are a mix- 

 ture of several kinds. Two only need to be mentioned since 

 they make up nearly the entire amount. These are casein 

 and albumin. The casein is that part of milk which curdles 

 on souring. It also gives the white color to the milk. In 

 cheese making rennet is added to the milk to coagulate the 

 casein, which takes most of the fat with it in a mechanical 

 way. The albumin is present to the amount of about 0.7 

 per cent. It is much like the albumin of an egg or that in 

 blood. It is coagulated by heating and may be seen as a 

 scum on the surface of boiled milk. It goes into the whey 

 in cheese making. 



The protein may be said to be the most valuable food con- 

 stituent of milk. It supplies material necessary for the growth 

 of bone and muscle and to keep up the repair of the body. 

 Part of the casein is in a semi-dissolved condition. A portion 

 of the undissolved part, and insoluble impurities that were 

 in the milk, make up the well-known separator slime. 



157. Sugar. The form of sugar known as lactose is found 

 only in milk. Its chemical composition is practically the same 

 as that of cane sugar, although it is less sweet in taste. It 

 has the same food value as ordinary sugar and like it fur- 



