MILK 37 



peroxydase, catalase, and reductase reactions have been 

 made use of in milk control work. 



Original and Bacterial Ferments. In milk hygiene 

 it is important to distinguish between original and bac- 

 terial ferments. An original ferment is one which is 

 secreted by the cells of the udder, or which is contained 

 in cells like the leucocytes and becomes free in the milk 

 when these cells disintegrate. A bacterial ferment is 

 secreted by the bacteria which gain access to milk after 

 it is formed in the udder. A bacterial ferment increases 

 in quantity after milk is drawn from the udder as a result 

 of the growth of bacteria, and if it is destroyed by heat 

 it will again appear unless the bacteria are all killed and 

 the milk is not reinf ected. On the other hand, an original 

 ferment cannot increase in quantity after the milk leaves 

 the udder, and if it is destroyed by heat it does not reap- 

 pear in the milk. Diastase and peroxydase are original 

 ferments, catalase is both an original and a bacterial 

 ferment, and reductase is a bacterial ferment. 



Diastase. One hundred c.c. of normal milk will di- 

 gest 0.015 to 0.02 gramme of starch in thirty minutes. 

 This action is due to an amylolytic ferment contained in 

 the milk, which has been called diastase. This ferment 

 operates best at a temperature of 45 C. (113 F.) and 

 is destroyed by a temperature of 65 to 68 C. (149 to 

 154 F.) for thirty minutes. It is present in the milk 

 when it is formed in the udder, and is therefore an orig- 

 inal ferment. It is not produced by bacteria. Colostrum 

 is richer in diastase than ordinary milk, and the ferment 

 is also present in greater quantity near the end of lac- 

 tation. The end milk contains more diastase than the 

 first milk drawn from the udder. (See diastase test on 

 page 297.) 



