168 AGRICULTURE. 



7 per cent. Butter fat is found In milk in the 

 form of minute drops of oil, called globules. 

 These globules vary in size from xoVir to ^^uwo 

 of an inch in diameter (see A, Fig. 37). The 

 number present in even a small amount of milk 

 is beyond comprehension. This fat is made up 

 of a mixture of ten or more distinct oils, the 

 more important of which are stearin, palmahn, 

 olei?i, and hutyrin. The first two mentioned 

 melt at a temperature above 140° F., while olein 

 is liquid at 32° F. The hardness of a certain 

 lot of butter depends upon the proportion of 

 these oils present. Green food, such as grass, 

 increases the proportion of olein, and accounts 

 for the soft condition usually observed in butter 

 made during the summer months. 



Butyrin is the characteristic fat of butter, and 

 is found only in butter fat. The chemical dif- 

 ference between butter and oleomargarine is 

 largely the absence of butyrin in the latter. 



The size of the fat globules (Fig. ■}^']) in milk 

 varies with the breed of the cow, the feed, and 

 with the individual animal. It is of some im- 

 portance on account of the relation it bears to 

 the separation of cream and to churning. Large 

 fat globules separate from the milk and form 

 cream more quickly than do small ones, and 

 with somewhat less loss of butter fat in the 

 skim-milk. Cream composed of large fat glo- 

 bules churns more rapidly. 



