BEHAVIOUR OF BACTERIA IN MILK 69 



In addition, single experiments at 60° C. with time exposures of 

 6, 23, 25, 28, 35, 45, and 60 minutes were all negative. 



+ = tuberculosis and — = no tuberculosis in the inoculated guinea-pig. 

 Each + or — sign represents a separate experiment. 



From these experiments Eosenau concludes that the tubercle 

 bacillus in milk loses its infective properties for guinea-pigs 

 when heated to 60° C. and maintained at that temperature 

 for 20 minutes, or to 65° 0. for a much shorter time. He 

 remarks : " It should be remembered that the milk in these 

 tests was very heavily infected with virulent cultures, indicated 

 by the prompt deaths of the control animals. Milk would 

 practically never contain such an enormous amount of infection 

 under natural conditions. It is justifiable to assume that if 

 60° C. for 20 minutes is sufficient to destroy the infectiveness 

 of such milk when injected into the peritoneal cavity of a 

 guinea-pig, any ordinary market milk after such treatment 

 would be quite safe for human use by the mouth so far as 

 tubercle bacilli are concerned." 



If the American results are accepted, it would seem that 

 a temperature of 60° C. maintained for 20 minutes is capable 

 of killing all tubercle bacilli in milk, especially if the conditions 

 preclude the formation of surface scum, while a much shorter 

 exposure is sufficient if 65° C. or 70° C. is employed. 



