INFLUENCE OF TIME ON BACTERIA IN MILK 



127 



2. The Influence of Time 



Having considered the effect of temperature upon micro- 

 organisms in milk, we may now direct our attention to what we 

 have, for the sake of convenience, termed the " influence of time." 

 It is, of course, obvious that under this title it is intended briefly 

 to summarise the changes which occur in milk during the period 

 which passes between its withdrawal from the cow, and its domestic 

 consumption. , 



As we have pointed out already, milk is a favourable medium 

 for organisms, and it will therefore be understood that finding 

 themselves in this suitable nidus, they commence rapid multi- 

 plication. Hence, in the course of a few hours after milking, the 

 milk remaining at an even temperature (namely, the temperature 

 of the surrounding air), there are vastly more bacteria in it, bulk 

 for bulk, than was the case at the actual time of milking ; and 

 when such milk, though naturally sterile, reaches the consumer, it 

 contains many thousands of bacteria in every cubic centimetre. 

 The following facts fully illustrate this. A sample of Berne milk 

 which shortly after milking contained 9000 bacteria per c.c. was 

 kept by Freudenreich at an even temperature of I5°C. It was 

 regularly examined during the next twenty-four hours with the 

 following result : — 



I hour after milking it contained . . . 3li7£0 bacteria per c.c. 



36,250 



40.000 



60,000 



120,000 



5,000,000 



Freudenreich gives another example which resulted in the 

 following figures : — 



Milk drawn at 15-5° C. 



After 4 hours at the same temperature 

 »> 9 j» It 11 



)> 24 „ „ „ 



contained 27,000 bacteria per cc 

 34,000 

 „ 100,000 „ „ 



„ 4,000,000 „ „ 



Conn furnishes an example of milk yielding the following 

 multiplication results : — 



