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, l^sually 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 destroj'ed 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. 



