1 86 BACTERIA 



be the vera causa. In addition to the fact that the high 

 numbers have but a limited significance, we must also re- 

 member that there is no uniformity whatever in these num- 

 bers. The conditions which chiefly control them are (i) 

 temperature, (2) time. 



The Influence of 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 bacterial growth. Freudenreich has 

 drawn up the following table which graphically sets forth 

 the effect of temperature upon bacteria in milk : 



3 hours. 6 hours. 9 hours. 24 hours. 



59 F i + ... 2.5 ... 5 ... 163 



77 F 2 ... 18.5 ... 107 ... 62,100 



95 F 4 1,290 ... 3,800 ... 5,370 



This instructive table claims some observations. It will 

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

 That may be accepted as a rule. At 77 F. the multiplica- 

 tion, though not particularly rapid at the outset, results 

 finally, at the end of the twenty-four hours, in the maxi- 

 mum quantity. These were probably common species of 

 saprophytic bacteria, which increase readily at a comparat- 

 ively low temperature. During the subsequent hours, after 

 the twenty-four, we should expect a decline rather than an 

 increase in 62,000, owing to the keen competition consequent 

 upon the limitation of the pabulum. From a consideration 

 of these figures we conclude that a warm temperature, some- 

 what 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. 



Let us take another example, from Professor Conn : 



