MILK 41 



reduction power because of the difference in the species 

 of bacteria present. But, according to B'arthel and O. 

 Jensen, when milk is stored under suitable conditions, 

 the relative proportion of the different species of bac- 

 teria present is almost always changed in favor of the 

 lactic acid organisms, so that in the case of market milk 

 there is usually correspondence between the reduction 

 time and the number of bacteria. 



The reduction power of a microorganism is not con- 

 stant, but depends upon the vitality of the organism; it 

 will therefore decrease with the age of the organism and 

 also when nutritive conditions are unfavorable. Hence, 

 the reduction activity of milk rich in bacteria is relatively 

 less than milk containing fewer bacteria. These factors 

 render the reductase test less exact than the plate method 

 for estimating the number of bacteria in market milk, 

 but not for judging the " keeping qualities " of the 

 milk, since the more vitally active the contained bacteria 

 the more rapidly will the milk undergo bacterial decom- 

 position. 



The reduction power of cream is greater than that 

 of skim milk. The reduction power is greatest just be- 

 fore curdling. In curdling, the ferment is precipitated 

 with the curd. The ferment operates best at a tem- 

 perature of 40 to 55 C. (104 to 131 F.) and is 

 destroyed by a temperature of 70 to 80 C. (158 to 

 176 F.). 



FM-Reductase. The knowledge concerning this 

 ferment is not sufficiently definite at this time to be of any 

 value in the practice of milk hygiene. FM-reductase 

 is present in colostrum on the first day after parturition 

 and is then absent from the udder secretion for two to 

 three weeks, when it again appears in the milk. Schern 



