126 



THE BACTERIAL CONTENT OF MILK 



Freudenreich found that bacteria in a sample of milk increased 

 in the following ratios when kept at the following temperatures : — 



If this table is read from above downwards, we obtain results 

 which reveal the effect of temperature. If it be read across, from 

 left to right, we obtain the effect of time upon bacterial multiplica- 

 tion. In the case of the temperature influence we see clearly the 

 very small multiplication at I5°C., and the excessive increase at 

 blood heat. This is the simple but fundamental point to be borne 

 in mind by the dairy bacteriologist. To refingerate milk as soon 

 as it is drawn from the cow is at once to check the increase of 

 bacteria. Obviously, such treatment is but one step short of radi- 

 cal, and in cases where the dairying from beginning to end is con- 

 ducted with strict cleanliness, and the milk is derived from healthy 

 cows, such refrigeration is ample protection. But where these con- 

 ditions are not fulfilled, the only safe course is in sterilisation or 

 pasteurisation of the milk. 



Another series of results from the same worker will illustrate 

 much the same point : — 



Samples of milk which shortly after milking contained 23,000 

 m.o. per c.c. were kept at 25° C. and 35° C. respectively, with the 

 following results : — 



We ourselves have carried out a number of experiments which 

 have invariably borne out the same principle as that enunciated, 

 namely, that the warmer the milk up to blood heat the more 

 marked is the increase of bacteria up to a certain point. As our 

 results have relation to the effect of time as well as temperature, 

 they will be considered at a later stage. 



