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 the temperature of the 

 surrounding medium it will, as a rule, 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 ordinary milk in 

 immense numbers, and under favorable conditions of 

 temperature multiply rapidly, feeding on the milk sugar 



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

 men from the total nitrogen in the milk, although 6.37 would be more 

 correct, since these substances, according to our best authorities, con- 

 tain on the average 15.7 per cent, of nitrogen ( y 1 -^ = 6.8?) 



