TIME AND TEMPERATURE 



185 



vcra causa. In addition to the fact that the high numbers have but 

 a limited significance, we must also remember that there is no 

 uniformity whatever in these numbers. The conditions which chiefly 

 control them are (1) time^and (2) temperature. 



The Influence of "Time and Temperature. We have already 

 noticed, when considering the general conditions affecting bacteria, 

 how potent an agent in their growth is the surrounding temperature. 

 Generally speaking, temperature at or about blood-heat favours bac- 

 terial growth. Freudenreich has drawn up the following table which 

 graphically sets forth the effect of temperature upon bacteria in milk: 



It will be noticed that at 59 F. there is very little multiplication. 

 That may be accepted as a rule. At 77 F. the multiplication, though 

 not particularly rapid at the outset, results finally, at the end of 

 the twenty-four hours, in the maximum quantity. These were 

 probably common species of saprophytic bacteria, which increase 

 readily at a comparatively low temperature. During the subsequent 

 hours, after the twenty-four, we should expect a temporary decline 

 rather than an increase in 62,000, owing to the keen competition con- 

 sequent upon the limitation of the pabulum. From a consideration 

 of these facts, we conclude that a warm temperature, somewhat below 

 blood-heat, is most favourable to multiplication of bacteria in milk ; 

 that the common saprophytic organisms multiply the most rapidly ; 

 that, in the course of time, competition kills off a large number. 



Another example may be taken from Professor Conn : 



Number of Bacteria per cubic centimetre in milk kept at different 

 temperatures. 



