174 BACTERIA IN MILE 
This is really a very useful function, for, whereas soured milk is 
wholesome, putrefied milk is not wholesome, and the lactic acid bac- 
teria thus protect the milk from a decomposition which would be 
far worse than souring. It has also come to be a recognized fact 
that many of the troublesome faults in milk may be remedied by 
using a culture of lactic acid bacteria. In cases of bitter milk, of 
premature curdling, and of other miscellaneous troubles, due to 
undesired bacteria, a remedy is found by putting into the milk a 
culture of a vigorous lactic acid bacterium that will grow rapidly 
and prevent the undesirable bacteria from developing sufficiently 
to cause trouble. The use of this principle in butter- and cheese- 
making has become very widely extended. 
It is this restraining action of the lactic acid bacteria that ex- 
plains the generally recognized fact that sour milk, or butter-milk, 
is not only a wholesome, but a very useful beverage. It seems a 
little strange that these products, containing as they do, bacteria 
reckoned by the hundreds of millions per c.c., should be recom- 
mended as beverages for invalids. <A glassful of well soured milk 
will certainly contain at least 100,000,000,000 bacteria, and yet it 
is a wholesome as well as a refreshing beverage. The explanation 
however, is simple enough. These myriads of bacteria are prac- 
tically all of the type of lactic acid bacteria, which are not only 
harmless in themselves, but which prevent the growth of various 
kinds of putrefactive germs that might produce trouble in the 
intestine. The presence of a goodly number of lactic acid bac- 
teria, therefore, may prevent the growth of certain types of in- 
testinal putrefaction that would otherwise cause trouble. The 
farmer’s belief that butter-milk and sour milk are healthful drinks, 
which seemed hardly credible for a while when the immense num- 
bers of bacteria contained in them were first recognized, appears, 
after all, to be well founded on scientific fact. The use of such 
milk is becoming recommended very widely, and already there are 
on the market commercial preparations of lactic bacteria to be 
used in preparing such milks. These preparations, as a rule, 
