206 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



more divergent. Woodhead reports that while in some 

 experiments a temperature of 140 F. (60 C.) killed 

 tubercle bacilli in 25 minutes, in others an exposure of 

 8 hours was required. Yersin, Bitter, Bonhoff, and other 

 investigators report that although an exposure to 140 

 F. (60 C.) for one hour was nearly always fatal to 

 tubercle bacilli, the effect was uncertain when the time 

 of exposure was much shorter. In Foster and Rull- 

 mann's experiments, the bacilli remained alive after 45 

 minutes at 140 F. (60 C.). DeJong asserts that tu- 

 bercle bacilli will survive heating at 159.8 to 161.6 F. 

 (71 to 72 C.) for y 2 hour, while Van der Sluis de- 

 clares that a temperature of 176 F. (80 C.) for 1 hour 

 is necessary to kill tubercle bacilli in naturally infected 

 milk. Hittcher considers 1 hour at 140 to 145.4 F. (60 

 to 63 C.) , 45 minutes at 147.2 to 149 F. (64 to 65 C.) , 

 or 30 minutes at 150.8 to 158 F. (66 to 70 C.) neces- 

 sary to destroy tubercle bacilli. On the other hand, Hew- 

 lett, in England, found that tubercle bacilli did not sur- 

 vive 30 minutes exposure to 140 F. (60 C.) and, in 

 this country, Rosenau found 20 minutes at 140 F., 

 Theobald Smith 15 minutes at 140 F., and Russell and 

 Hastings 10 minutes at that temperature sufficient to 

 kill the organisms. Hewlett and the American investi- 

 gators used in their experiments milk artificially in- 

 fected with tubercle bacilli, while nearly all, if not all, 

 of the other experiments mentioned were made with 

 naturally infected milk. 



The conditions were therefore by no means the same. 

 In naturally infected milk, the tubercle bacilli are em- 

 bedded in masses of mucus, clots of fibrin, or shreds of 

 tissue, and this albuminous covering protects them from 

 the action of the heat. It is true that in those experi- 



