MILK 41 
reduction power because of the difference in the species 
of bacteria present. But, according to Barthel 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 microérganism 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 181° 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. F'M-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 
