SECTION v.— DAIRY PRODUCTS 



CHAPTER XIX 



Milk 



Milk is the natural secretion of special glands of female mam- 

 mals, and being intended for the nourishment of newly bom 

 animals, naturally contains all the nutrients required for their 

 maintenance and growth, namely, protein, fat, carbohydrates, and 

 mineral salts. The proportions of these constituents vary largely 

 in the case of different animals, but in the case of any one species 

 of animal, such as the cow, the percentages do not usually vary 

 between wide limits. 



From the point of view of milk-production for domestic pur- 

 poses, the cow is by far the most important, and in this volume 

 the word milk applies to cows' milk, unless stated definitely to the 

 contrary. 



ICO-OO ,, 



The protein in milk consists of casein (85 per cent.), lacto- 

 albumin (15 per cent.), and lacto-globulin (traces), and of these 

 the lacto-albumin is coagulated by heat (70° C), the casein is 

 precipitated by rennet or dilute acids, while the lacto-globulin 

 is thrown down by the action of mineral salts {e.g. MgS04). 



Colostrum. — The udder secretion immediately before and after 



175 



