FERMENTS IN MILK. 53 
approximately twenty minutes for this process of fission to 
take place. 
Some germs develop small bodies within the cell, called 
spores. It is not difficult to destroy the sporeless cell by 
heat, but the spores are very resistant to unfavorable con- 
ditions. The spore-bearing bacteria cannot be destroyed by 
boiling. The heating destroys the vegetative cell, but the 
spores still remain. In order to destroy the germ in the spore 
form, it is essential that the milk be cooled to a temperature 
favorable to growth, and then allow the spore to develop into 
a vegetative cell. If heat is again applied, the milk can be 
rendered entirely sterile. Usually three or four successive 
heatings and coolings are necessary in order to render the milk 
completely sterile. A single heating under pressure (15 minutes 
at 15 pounds) kills them at once. 
It has been demonstrated by several investigators that 
freshly drawn milk is not a good medium for bacteria to develop 
in. In fact, several experiments seem to indicate that milk 
acts as a germicide to certain varieties of bacteria. For instance, 
the cholera germ is to some extent destroyed in fresh milk, 
but it is not known to what extent. Organisms producing 
lactic acid check the multiplications of these pathogenic bac- 
teria. This germicidal property is said to be common, to a 
greater or less extent, to all the animal secretions. 
Effect of Thunder-storms on Souring of Milk.—It is a common 
impression that thunder-storms hasten the souring of milk. 
This was attributed to the electricity in the air accompanying 
the storm. Experiments by several investigators have proved 
that electricity does not have any effect on hastening the fer- 
mentative changes of milk. The reason why milk sours quicker 
when an electrical storm is approaching, is that the air tem- 
perature is usually higher then than at any other time. This 
higher temperature warms the milk and creates more favor- 
able conditions for the rapid multiplication of the germs present 
in the milk. It is for this reason that milk sours quicker during 
or previous to a thunder storm than at any other time. 
