EFFECT OF TEMPERATURE. IOI 



the fewer may have far the larger number. The following 

 two experiments illustrate the point, the two samples being 



FIG. 20. 



/ 



a 



Showing the effect of temperature upon bacteria growth, a, a single bacterium ; b, its 

 progeny in twenty-four hours in milk kept at 50, 5 bacteria ; c, its progeny in twenty-four 

 hours in milk kept at 70, 750 bacteria. Figures taken from an actual experiment. 



milk from the same cow obtained upon different days but 

 kept in identical conditions. Here it will be seen that the 

 sample that started with the smaller number finally ended at 

 fifty hours .with far the larger number. To what such 

 idiosyncrasies are due it is quite impossible to say. 



FRESH MILK. FIFTY HOURS OLD. 



November 23, Number per c.c 3,600 2,090,000,000 



November 25, Number per c.c 7,400 49,600,000 



Effect of Temperature upon Different Species of Bacteria. 



Different bacteria are very differently affected by tempera- 

 ture. Some species grow best at low and others at high tem- 

 peratures. Of the dairy bacteria those which develop in milk 

 at 50 are commonly different from those that grow at 

 higher temperatures. At 50 the Bact. lactis acidi type 

 hardly grows at all, and the bacteria which multiply in the 

 milk at the close of the initial germicidal period belong to 

 other types than the common lactic bacteria. As a result 

 the milk can be kept at this temperature for a long time 



