64 MILK AND THE PUBLIC HEALTH CHAP. 



strains of typhoid bacilli. His results showed that in milk 

 heated to 60 C. and maintained at that point for 2 

 minutes all the typhoid bacilli were killed. The great 

 majority of these organisms were killed by the time the 

 temperature reached 59 C. A few survived to 60 C. 



B. diphtheriae. Welch and Abbott, also Koux and Yersin, 

 have tested the thermal death-point of this bacillus in broth, 

 sterile salt solutions, etc. Both sets of observers found that 

 10 minutes' exposure at 58 C. killed the bacilli. 



Eosenau (loc. cit.) found that diphtheria bacilli succumb 

 at comparatively low temperatures. Frequently they failed 

 to grow after heating to 55 C., but some occasionally survived 

 until the milk reached 60 C. Eosenau only used one strain 

 of diphtheria bacillus, but carried out ten different experi- 

 ments. 



Vibrio cholerae. Kolle, Kutscher, Meinicke, and Friedel 

 found that this vibrio was not killed in milk until a tempera- 

 ture of 60 C. was reached. In their experiments it took 7 to 

 8 minutes for the milk to reach this temperature. 



Rosenau carried out eighteen experiments. He concluded 

 that the cholera vibrio is similar to the diphtheria bacillus so 

 far as .its thermal death-point is concerned. It was almost 

 invariably destroyed when the milk reached 55 C., and only 

 once did it survive to 60 C. under the conditions of the 

 experiments. 



B. dysenteriae. Eosenau found this bacillus somewhat 

 more resistant to heat than the typhoid bacillus. He found 

 that it sometimes withstood heating at 60 C. for 5 minutes. 

 All were killed by exposing to 60 C C. for 10 minutes, while 

 the majority were killed by the time the milk reached 60 C. 



Micrococcus melitensis. Dalton and Eyre 1 carried out a 

 series of experiments, and found the thermal death-point to 

 be 57*5 C. with a fixed time exposure of 10 minutes. They 

 used five different strains of micrococcus. They did not, 

 however, test the organism in milk. Eosenau carried out 

 three experiments with this organism in milk. He found 

 that it was not destroyed at 55 C. for a few minutes (4-|), 

 that the great majority die at 58, and at 60 C. all are 

 destroyed. He concluded that 60 C. for 20 minutes is more 



1 Journ. of Hygiene, 1904, iv. p. 157. 



