Composition of Milk and Its Products. 15 



milk, obtained by multiplying the total nitrogen con- 

 tent of the milk by 6.25. 1 



The quantity of casein in normal cow's milk will vary 

 from 2 to 4 per cent., and of albumen, from .5 to .8 per 

 cent. The total content of casein and albumen ranges 

 between 2.5 and 4.6 per cent, the average being about 

 3.2 per cent. Milk with a low fat content will contain 

 more casein and albumen than fat, while the reverse is 

 generally true in case of milk containing more than 3.5 

 per cent, of fat. 



19. Milk sugar or lactose belongs to the group of 

 organic compounds known as carbohydrates. It is a 

 commercial product manufactured" from whey and is 

 obtained in this process as pale white crystals, of less 

 sweet taste and less soluble in water than ordinary 

 sugar (cane sugar, sucrose). About 70 per cent, of the 

 solids in the whey, and 33 per cent, of the milk solids, 

 are composed of milk sugar. 



When milk is left standing for some time, viz., from 

 one to several days, according to its cleanliness and 

 the temperature of the surrounding medium, it will 

 turn sour and soon become thick and loppered. This 

 change in the composition and appearance of the milk 

 is brought about through the action of acid-forming 

 bacteria on the milk-sugar. These are present in ordi- 

 nary milk in immense numbers, and under favorable 

 conditions of temperature multiply rapidly, feeding on 



1 The factor 6.25 is generally used for obtaining the casein and albu- 

 men from the total nitrogen in the milk, on the theory that protein 

 compounds contain 16% N. ; the factor 6.37 would, however, be more 

 correct, since casein and albumen, according to our best authorities, 

 contain on the average 15.7 per cent of nitrogen 



