BEHAVIOUR OF BACTERIA IN MILK 65 



than siifficient to destroy the infective principle of Malta fever 

 in milk. 



B. tuherculosis. — Special difficulties have been met with in 

 determining the thermal death-point of this bacillus in milk, 

 and decidedly discrepant results have been obtained by different 

 workers. Part of the difficulty is due to the fact that the only 

 way to ascertain whether the tubercle bacilli are alive or 

 not after the heatiug is by animal inoculation, and the lesions 

 produced by the injection of dead tubercle bacilli somewhat 

 closely resemble those resulting from injection of the living 

 bacilli. The discrepant results are also in part to be accounted 

 for by the bacilli not being always in uniform emulsion. In 

 this country experiments have been carried out by Woodhead, 

 by Macfadyen and Hewlett and others. 



Woodhead ^ obtained discordant and contradictory results. 

 For example, in some experiments 25 minutes at 60° C. killed 

 the tubercle bacilli, in others 8 hours was required. 



Hewlett and Macfadyen ^ found that almost invariably 

 milk, to which powdered dry sputum had been added, was 

 remlered free from living tubercle bacilli by momentary heating 

 to 67'-68° C. 



Hewlett^ carried out a few further experiments with 

 artificially inoculated milk. He found that tuberculous milk 

 heated to 60° C. for 30 minutes failed to produce tuberculosis 

 in guinea-pigs, while also such milk contained no living 

 tubercle bacilli after 20 minutes at 68°-65° C. in an AUenbury 

 pasteuriser. 



The Continental findings are discrepant. They are rather 

 numerous and only a few can be mentioned. The earlier 

 results of Yersin, Bitter, Bonhoff, Forster, etc., showed that 

 while 60° C. for one hour was nearly always fatal to the 

 tubercle bacillus, the effect of a much shorter time exposure 

 was very variable. De Man's * results are frequently quoted, 

 but lie did not work with tubercle bacilli in milk, and his 

 fiiiilin^is obtained by using the cheesy substance scraped from the 

 cut surface of tuberculous udders cannot be applied to tubercle 

 bacilli naturally occurring or even artificially added to milk. 



1 Royal Commission Report, 1895, p. 145. 



2 Trans. Brit. Inst, of Prev. Med. vol. i. 



3 Joxim. of State Med., 1900, viii. p. 754. 



4 ArcUv.f. Sycj., 1893, xviii. p. 133. 



