TYPES OF BACTERIA FOUND IN MILK 16 5 
to a temperature of boiling water. Such milk still contains a 
considerable number of spore-bearing bacteria that resist this 
temperature. The milk does not sour, inasmuch as all lactic acid 
bacteria are killed, since they never produce spores. The class of 
enzyme-forming bacteria, however, are very commonly spore 
bearers, and resist the temperature of boiling water. Milk which 
has been boiled, therefore, not infrequently undergoes changes 
which affect its taste and its chemical nature, due to the class of 
bacteria here considered. Occasionally they are of significance in 
cheese-making. During the long ripening of cheese they have a 
better chance to grow than in milk. Whether they have much 
influence upon hard cheeses seems doubtful, but in the ripening of 
soft cheeses they sometimes produce very bad results, causing 
much loss to the cheese-makers. While, therefore, they are of 
little importance to the one who handles milk, they play a consid- 
erable part in the making of cheese. 
This class of liquefying bacteria usually produces no acid; 
but there is a small group of the same class that differs from the’ 
others in producing both a digesting enzyme and an acid. They 
are sometimes called acid liquefiers. It has been thought that they 
play a part in the ripening of cheese, but this is by no means 
certain and in general they are of little significance. 
Udder Cocci.—When freshly drawn from the udder, without 
exterior contamination, milk contains various kinds of cocci, 
If this carefully drawn milk is kept at body heat, these cocci de- 
velop to large numbers; but in ordinary market milk they are 
comparatively few. Many of these are of the Micrococcus type 
and appear to come just as frequently from healthy as from dis- 
eased udders. Others are of the Sivepiococcus type, and form long 
chains (see Fig. 9, d, page 13). The Streptococci, as already men- 
tioned (page 149) come from infected udders, and are often found 
in large numbers in the milk from cows having garget. 
If these cocci are grown in milk in the absence of all other 
organisms, they produce acid, but under practical conditions, 
