14 Dairy Bacteriology. 



that the process of cell division under favorable condi- 

 tions takes place in a few moments. Barber has shown 

 that one of the forms of bacteria constantly found in 

 milk will divide in 17 minutes at 98 F. and that a single 

 organism kept at this temperature for ten hours would 

 increase to 1,240,000,000. If the temperature is reduced 

 to 50 F., the time required for division is increased to 

 several hours. The explanation for the rapid spoiling of 

 milk that is not well cooled is thus apparent. The in- 

 itial rapid rate of increase cannot be maintained for any 

 length of time as the conditions become more and more 

 unfavorable as growth continues, due to the accumu- 

 lation of the by-products of the cell activity. Thus, the 

 growth of acid-forming organisms in milk becomes 

 checked by the formation of acid from the fermentation 

 of the sugar. 



Detrimental effect of external conditions. Environ- 

 mental conditions of a detrimental character are con- 

 stantly at work tending to repress the activity of bac- 

 teria or to destroy them. These act more readily on the 

 vegetating cells than on the more resistant spores. It 

 is of the utmost importance that those engaged in dairy 

 work be familiar with these antagonistic forces since it 

 is constantly necessary to repress or to kill outright the 

 bacteria 'in milk and other dairy products. In many 

 lines of dairy work it is likewise important to be familiar 

 with the conditions favorable for bacterial growth. 



Effect of cold. While it is true that chilling largely 

 prevents fermentative action, and actual freezing stops 

 all growth processes, still it' does not follow that expo- 

 sure to low temperatures will effectually destroy the 

 vitality of bacteria, even in the growing condition. 

 Numerous non-spore-bearing species remain alive in ice 



