35 
intravenous injection of a culture. ' Some of this spleen pulp, very 
rich in bacilli, was drawn into capillary tubes hermetically sealed and 
plunged into a water bath kept at the desired temperature. After 
heating, the pulp was inoculated upon glycerine bouillon. Tubes 
heated to 55° for ten minutes gave subsequent growth; those heated 
to 60° for ten minutes, no growth; those heated to 70° for ten min- 
utes, no growth. The tubercle bacilli ^Svith spores” came from an 
old culture in glycerin bouillon. Tubes heated to 55° for ten min- 
utes gave subsequent growth; those heated to 60° for ten minutes 
gave subsequent growth; those heated to 65° for ten minutes, no 
growth; those heated to 70° for 10 minutes, no growth. 
Yersin concludes that the bacillus of tuberculosis resists a tem- 
perature of 60° C. for ten minutes, and that it is remarkable that the 
resistance of the “spores” to the heat is not greater than that of the 
bacilli themselves. He made no tests upon animals. 
He found, contrary to the work of Schill and Fischer, that tuber- 
culous sputum heated to 100° for two minutes is always sterile. 
Thus early in the history of these investigations the idea became 
prevalent that the tubercle bacillus possessed a resistance to heat 
considerably greater than that of other nonspore-bearing pathogens. 
Indeed, at this time the tubercle bacillus was regarded by many as 
occurring in a spore-bearing form, and some of the writers spend 
much time in telling whether the strains they used were spore-bear- 
ing or not, omitting more pertinent facts. 
Bitter,® 1890, accepted the results of Yersin to the effect that the 
tubercle bacillus when evenly distributed through milk is killed by 
an exposure to 75° C. for ten minutes, and inquires if a lower tem- 
perature, desirable for practical reasons, might not be equally 
efficacious. He cautiously descends as far as 68° to 69°, and finds 
that milk to which infected sputum had been added and placed in 
test tubes immersed in a previously warmed water bath is rendered 
innocuous to guinea pigs inoculated intraperitoneally, if the exposure 
has lasted as much as twenty minutes. Controls injected with the 
unheated milk died of tuberculosis in five weeks. To be perfectly 
safe, the author recommends that the exposure to 68°-69° be increased 
to thirty minutes. v 
Bang,^ 1891, states that his experiments demonstrate that heating 
to 85° C., and sometimes even to 80° C., kills all the tubercle bacilli; 
that heating for five minutes to 70° C., sometimes to 60° C., so enfee- 
« Bitter, H.; Versuche iiber das Pasteurisiren der Milch. Zeit. f. Hyg., vol. 8, 
1890, p. 240-286.. 
&Bang; Le danger suppose de la consommation du lait et de la viande sains en 
apparence mais provenent d’animaux atteints de la tuberculose. Trans, internal. 
Cong. hyg. et demog., 1890, p. 193. Also: Experimentelle Untersuchungen iiber 
tuberculose Milch. Deut. Zeit. f. Tiermed., vol. 17, 1891, p. 1. 
