12 MODERN METHODS OF TESTING MILK 



have attracted much attention in recent years, namely, 

 milk-enzyms. These are present in very small amounts 

 and have never been isolated in pure forms but they 

 are thought to be nitrogen-containing compounds. 

 They are chemical ferments and have the power of 

 changing other substances without themselves under- 

 going appreciable change. Methods of ascertaining 

 their presence in milk are given later (pp. 158-163). 



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. Milk-casein varies in 

 amount from 2 to 4 per 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 forms 

 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 per 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. 



