18 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



but these advantages are overbalanced by the expense 

 of the process. 



When milk is shaken or agitated the fat globules 

 gradually unite and form flakes or lumps i.e., butter. 

 Small clumps of butter fat may form in milk during 

 transportation when the container is not full. This 

 change may affect the test for fat. If milk or cream 

 is slightly acid and warm, the clumping of the fat glo- 

 bules is facilitated. Hence cream is usually churned 

 after it has attained an acidity 0.4 per cent., and at a 

 temperature of 21 C. (70 F.). Cream from a cow 

 near the end of lactation may not "butter" because of 

 its alkalinity. 



The fat of milk differs in its chemical and physical 

 properties from both the fat of the tissues and the fat 

 of the food. It consists of a mixture of fats, princi- 

 pally olein, stearin, and palmatin, together with some 

 butyrin and other fats. Its composition varies, being 

 influenced by the breed, feed, external conditions, etc. 

 Cotton-seed meal, for example, increases the olein and 

 raises the melting point. When milk fat decomposes, 

 butyric acid is liberated and produces a rancid odor and 

 taste. The color of the milk fat is more or less yellow. 

 The fat globules, by reflecting the light, are partly re- 

 sponsible for the opacity of milk. 



In regard to the origin of the milk fat, it appears 

 most probable that it is derived in part from the splitting 

 up of albuminous compounds in the udder or in another 

 part of the body, or in both places. It may also be formed 

 from the carbohydrates which are carried to the udder 

 by the blood (Rievel). 



Lactose. This substance, also known as "milk 

 sugar," is in solution in milk. It is a disaccharid and 



