PASTEURIZATION 201 



resulting from the effects produced by dead tubercle bacilli, 

 doubtful lesions were carried over into another animal. 



From these experiments it is evident that the tubercle 

 bacillus in milk loses its infective properties for guinea- 

 pigs when heated to 60° C. and maintained at that temper- 

 ature for twenty minutes, or to 65° C. for a much shorter 

 time. 



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 in- 

 fection under natural conditions. It is justifiable to assume 

 that it 60° C. for twenty minutes is sufficient to destroy 

 the infectiveness of such milk when injected into the peri- 

 toneal cavity of a guinea-pig, any ordinary market milk 

 after such treatment would be safe for human use by the 

 mouth so far as tubercle bacilli are concerned. 



It is difficult, if not impossible, to briefly summarize the 

 work of others upon the thermal death-point of the tubercle 

 bacillus in milk. The following table (see page 202) neces- 

 sarily leaves out many factors. 



The tabular statement shows that my results agree 

 with the work of Yersin, Bonhoff, Schroeder, Th. Smith, 

 Russell and Hastings, Hesse, and Rosenau in that 60° 

 for twenty minutes is sufficient to kill the tubercle ba- 

 cillus. 



The lesions produced by a large mass of dead tubercle 

 bacilh may be distinguished by their extent rather than 

 by their character. In doubtful cases secondary inocula- 

 tion is the only trustworthy method of determining whether 

 the bacilli are alive or dead. The tuberculin test does not 

 differentiate between the live and dead tubercles. Three 

 guinea-pigs out of eight having lesions produced by dead 

 tubercle bacilh (killed at 100° C.) died as the result of the 

 subcutaneous inoculation of tW cubic centimetres tuber- 

 culin (O. T.). 



