SOURCES OF BACTERIA IN MILK 63 



spores. It is not difficult to destroy the sporeless cell by heat, 

 but the spores are very resistant to unfavorable conditions. 

 The spore-bearing bacteria are difficult to kill ; boiling for a short 

 time will not destroy them. Hammer is satisfied that they are 

 destroyed by prolonged boiling. Another method is to heat the 

 milk to destroy all the organisms in the vegetative stage, then 

 cool it to a temperature favorable to growth and allow the spores 

 to develop into the vegetative stage, and again apply heat. In 

 this way milk can be rendered entirely sterile. A single heating 



FIG. ii. The wrong and the right kind of a milk-pail. A, the ordinary type of 

 pail showing sharp angle between sides and bottom; B, the same properly 

 flushed with solder so as to facilitate thorough cleaning. The lower figure 

 represents a joint as ordinarily made in tinware. The depression a affords 

 a place of refuge for bacteria from which they are not readily dislodged. This 

 open joint should be filled completely with solder. (From Bui. 62, Wis.) 



under pressure (fifteen minutes at 1 5 pounds pressure) 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 bacteria. This germicidal 

 property is said to be more or less common to all the animal 

 secretions. 



