40 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
dinger’s reagent, and a little of this solution is added to 
milk, the mixture will also be colored blue, but the color 
will disappear more rapidly. At first the difference in 
the time of reduction was attributed to the difference in 
the composition of the solution, but further research 
demonstrated the presence in milk of two different re- 
ducing agents. The ferment which reduces the methylene 
blue solution is called “‘ M-reductase,” while the one 
which reduces the formalin-methylene blue solution has 
been named “ F'M-reductase.” 
M-Reductase.—This ferment is not secreted in the 
udder with the milk. It is generally regarded as of 
bacterial origin, although the opinion has been expressed 
(Burri and Kiirsteiner) that the cellular elements of 
milk, like all living protoplasm, have a reduction power 
and that the high reduction power of colostrum during 
the first day after parturition and of mastitis milk is due 
to the rich cellular content of these secretions. It has 
been well established, however, that the capacity of milk 
to reduce methylene blue increases with the number of 
bacteria. 
The different species of bacteria vary in their reduc- 
tion power. Reduction power appears to depend first 
upon the species, then upon the number of bacteria, and, 
finally, upon the media in which the organisms are grow- 
ing. The anaerobic organisms usually have a greater 
reduction power than the aerobes, while the facultative 
anaerobes act more powerfully in the absence of oxygen 
than when it is present. The colon bacilli belong to the 
facultative anaerobes of high reduction power. On the 
other hand, the reduction power of the lactic acid bacteria 
is weak. Different samples of fresh milk containing 
about the same number of bacteria may differ greatly in 
