208 BACTERIA IN BUTTER AND OLEOMARGARINE 
readily in warm than in cold temperatures. At temperatures be- 
low freezing rancidity does not occur. If butter is, therefore, kept 
cool and in large masses, it may be held for a long time without 
the appearance of any very noticeably strong flavor. In the end, 
however, the rancidity is sure to appear. To what extent bacteria 
are concerned in this change we do not yet know, although most 
investigators have concluded that they are prominently concerned 
in the phenomenon. Rancidity may certainly be looked upon as 
a fermentation change, and the only method the dairyman has of 
controlling it is by cool temperatures, by packing the butter in 
large masses, by paraffining the butter tubs, and by keeping it from 
the light. It may be delayed by pasteurizing the cream and 
by using pasteurized water for washing, facts that show its close 
relation to bacteria. Fortunately, it is a matter of no very great 
importance, because butter can be kept without difficulty for some 
months, and it is almost always possible to market it before it has 
spoiled. 
BACTERIA IN OLEOMARGARINE PRODUCTS 
The materials out of which oleomargarine is made are chiefly 
stearin, lard, cottonseed oil, and other oils. These are warmed to 
the melting-point, are thoroughly mixed, and then drawn off into 
cold brine, which chills the oils into a hard mass. The process 
is certainly a useful method of utilizing quantities of oils which 
would otherwise be waste products. It makes a wholesome, 
digestible food, which could have no objection raised against it 
if it could only be sold upon its own merits, instead of under the 
false guise of butter. In order to make the product the more 
resemble butter, it has been customary to color it; but this prac- 
tice is now largely prevented by a prohibitive tax on colored oleo- 
margarine. The bacteria normally present in oleo products are 
commonly much less numerous than in butter, and the oleomar- 
garine is, on the whole, less likely to distribute infectious diseases 
