12 MODERN METHODS OF TESTING MILK 



ing able to coai^'iilate milk-casein and then digest it 

 or make it soluble. It is ])resent in very small amounts 

 in milk and its action is very slow. It has never been 

 isolated from milk in \)Uvq form. It is ])robably a nitro- 

 gen-containing substance. Our knowledge of galac- 

 tase is very far from complete. 



Amounts of casein and albumin in milk. — In single 

 milkings of individual cows, the casein and albumin, 

 taken together, vary from 2.5 to 6 per cent, and 

 average about 3.2 per cent. INIilk-casein varies in 

 amount from 2 to 4 j^er cent, and averages about 2.5 

 per cent. Albumin varies from 0.5 to 0.9 per cent. 

 and averages about 0.7 per cent. The amount of ca- 

 sein in relation to albumin varies greatly. On an 

 average, milk contains about 3.6 parts of casein for 

 one of albumin, or, stated another way, casein consti- 

 tutes about 80 per cent, of the nitrogen compounds of 

 milk. 



The amount of casein and albumin in milk is influ- 

 enced by many conditions, such as influence the gen- 

 eral composition of the milk, among which are individ- 

 uality, breed, advance of lactation, etc. As the lacta- 

 tion period advances, there is a general tendency on 

 the part of casein and albumin in milk to increase. 



Relation of fat and nitrogen compounds in milk. — 

 In normal milk containing over 3 ])er cent, of fat, the 

 amount of casein and albumin is rarely greater than 

 the amount of fat, especially in the milk of herds of 

 cows. When the per cent, of fat is less than that of 

 the nitrogen compounds, the milk may generally be 

 regarded as skimmed, especially in the case of milk 

 from herds. 



