42 Dairy Bacteriology. 



Although different species vary in their rate of devel- 

 opment, yet moderately warm" temperatures from 75 to 

 90 F., encourage rapid growth. Unless the milk is 



PROGENY Or A 



SINGLE GERM 

 IN TWELVE: HOURS 



FIG. 11 Showing the effect of cooling milk on the growth of bacteria. The 

 beneficial results of early chilling are readily apparent. 



quickly deprived of its original heat, the rate of the fer- 

 mentative changes will be much increased as is shown in 

 following results obtained by Cnopf and Escherich : 



Rate of growth of single germ 



2 hrs. 3 hrs. 4 hrs. 5 hrs. 6 hrs. 



54 F 4 6 8 26 435 



97 F 23 60 215 1830 3800 



If a can of milk is allowed to cool naturally, it will take 

 several hours before it reaches the temperature of the 

 surrounding air. During this time, the organisms in 

 the fore milk are continuing their rapid growth, while 

 those forms that come from dust, and are presumably 

 in a latent state on account of their condition, awake 

 from their lethargy under the influence of these favora- 

 ble surroundings. If bacteria once gain an entrance and 

 begin to germinate, a considerably lower temperature is 

 required to successfully check development than to hold 



