2. MILK 



tated by many substances, among which are 

 acids, rennet, and magnesium sulfate, but not 

 by heat. Acids precipitate it by breaking up 

 the combination with phosphates. The action 

 of rennet is complex and probably partly hy- 

 hydrolytic, splitting the casein into several 

 proteins, some of which are precipitated in 

 the curd. Films of protein matter occur abun- 

 dantly in milk, for which reason it is distinctly 

 opaque, even when nearly all the fat has been 

 removed by contrifugal action. 



The albumin of milk appears to be a distinct 

 form, and is called lactalbumin. It is not 

 precipitated by dilute acids, but is coagulated by 

 heating to 70° — 75°. The proportion in cow's 

 milk is usually from 0.35 to 0.50%, but col- 

 ostrum may contain much larger proportions. 



Globulin is present only in minute amounts 

 in normal milk, but colostrum may contain as 

 much as 8%. It is coagulated on heating. 



Lactose. — This is a sugar peculiar to milk. 



Citric acid is a normal constituent of the nulk 

 of various animals. In human milk, the quantity 

 is about 0.5 gram to 1000 c.c; in cow's milk, 

 from I to 1.5 grams. It is not dependent on 

 the citric acid present in the food. 



Enzyms. — Several enzyms occur in milk but 

 they are chiefly known by effects and not as 

 isolated substances. Some are proteolytic, others 



