98 GROWTH OF BACTERIA IN MILK. 







SAME MILK AFTER 6 

 FRESH MILK. HOURS AT 70 F. 



No. of bacteria per c.c 1,950 1,900 



32,000 23,600 



13,000 9,175 



After a time this decrease in bacteria ceases and then 

 begins an increase, which soon becomes very rapid. The 

 length of time during which this initial decline, or failure 

 to increase continues, is variable and depends, among other 

 things, upon the temperature. At a high temperature 

 (90 F.), it is short, being not more than three hours. At 

 70 it is longer, lasting from six to nine hours or even more. 

 At about 50 it lasts longer yet, and milk at this temperature 

 will remain frequently for forty hours without showing any 

 increase in bacteria, and commonly at thirty hours will 

 actually contain fewer bacteria than at the start. In all cases, 

 however, this period of initial decline eventually comes to an 

 end, and the bacteria begin to grow more or less rapidly. 



To what this initial decline of bacteria is due is not known. 

 It has been attributed to what has been called the " germi- 

 cidal power " of milk, the assumption being that there is 

 present in milk some substance which acts unfavorably 

 upon the bacteria, a substance akin to the similar supposed 

 substance existing in fresh blood. By others the phenom- 

 enon has been attributed simply to the fact that the bacteria 

 which get into the milk are placed at once in a medium for 

 which they are not immediately adapted. Some of them are 

 so unfavorably affected that they do not grow at all and 

 soon die, while others require some little time to adapt them- 

 selves to the new medium. There is consequently a short 

 period during which a few poorly adapted forms disappear 

 while others are adapting themselves to the new conditions 

 before they begin any rapid growth. During this time 

 there is no noticeable growth of any species, but an actual 

 disappearance of some of the poorly adapted forms. If this 

 is the explanation, it is not proper to speak of any germicidal 



