324 PRODUCTIVE FARMING 



is always a little albumen present. It is similar to the white 

 of raw egg. The casein is the main tissue-forming part of 

 the milk when used as food. 



Milk sugar is the heat-producing part of milk when used 

 as food. When milk sours it is due to the action of bacteria 

 which changes the sugar into an acid, called lactic acid. 



The mineral matter in milk is made up of the same minerals 

 required by the bones and other body tissues. They are 

 very beneficial when milk is used as human food. When 

 milk is pasteurized by heating, it loses much of the mineral 

 value and is no longer a suitable food for growing children. 

 The bones are apt to be too soft when such milk is used 

 regularly. 



Composition Varies Naturally. — The milk from dairy 

 animals varies in its composition from several causes. The 

 main factors are given below : 



1. Breed of animal; as Jerseys have more fat in the milk 

 than Holsteins. 



2. Period of lactation; the milk being richer in fat just 

 before a cow dries up. 



3. Different parts of same milking; the first is poor in 

 fat, the last is rich. 



4. Kinds of feed; this influences quantity of milk chiefly; 

 but the character of butter fat is influenced by feed; for 

 example, cottonseed meal makes the fat harder than does 

 linseed meal. 



Exercise. — Difference in Milk. — Have one of the pupils 

 or a farmer save in two separate bottles some of the first 

 of the morning's milking and some of the strippings from 

 the same cow. One-fourth pint of each will be enough. 

 These two bottles may be kept in a cool place for a day 

 until the cream has all risen. The difference will then be 

 shown by measuring the thickness of the layer of cream in 

 each bottle. It is not a bad plan to use the first pint of each 

 milking for pigs or calves instead of for human food. 



