BACILLI IX CHRONIC INFECTIOUS DISEASES. 473 



of spores. But, so far as resistance to heat is concerned, this is not 

 so great as was at one time believed. Schill and Fischer (1884), as- 

 suming that the tubercle bacillus forms spores, made quite a number 

 of experiments to determine its thermal death-point. They sub- 

 jected sputum containing the bacillus to a temperature of 100 C., and 

 tested the destruction of vitality by inoculations into guinea-pigs. 

 Exposure to steam at a temperature of 100 C. for two to five min- 

 utes was effective in every experiment, with one exception. One 

 guinea-pig died tuberculous after having been inoculated with 

 sputum exposed to this tamperature for two minutes. This result 

 was assumed to show that the bacillus would survive lower tempera- 

 tures, but it is evident that additional experiments were required to 

 establish this fact. In 1887 the writer made a few similar experi- 

 ments at a lower temperature, and guinea-pigs inoculated with tuber- 

 culous sputum exposed for ten minutes to a temperature of 90, 80, 

 and 60 C. failed to become tuberculous, while another guinea-pig, 

 inoculated with the same material after exposure to a temperature of 

 50 C. for ten minutes, died tuberculous. These results correspond 

 with those subsequently (1888) reported by Yersin, who tested the 

 thermal death-point of this bacillus by the culture method. This 

 author assumes that the bacilli form spores, but states as a result of 

 his experiments that "at the end of ten days bacilli heated for ten 

 minutes at 55 C. gave a culture in glycerin-bouillon ; those heated 

 to 00, at the end of twenty-two days; while those heated to 70 and 

 above failed to grow in every instance. This experiment, repeated a 

 great number of times, always gave the same result. The tubercle 

 bacilli then resist a temperature of 60 C. for ten minutes, and it is 

 to be remarked that the resistance of spores to heat appears to be no 

 greater than that of the bacilli themselves." Yersin remarks in a 

 footnote that "the spores which served for these experiments did 

 not appear as more or less irregular granules taking the coloring 

 matter strongly, but as veritable spores with sharply defined outlines, 

 to the number of one or two in a bacillus, or three at the outside. 

 These spores are particularly clear in cultures upon glycerin-agar 

 several weeks old." 



It may be that bacteriologists have been mistaken in the infer- 

 ence that all spores possess a greater resisting power for heat than 

 that exhibited by bacilli in the absence of spores. That this is true 

 as regards anthrax spores and many others, the thermal death-point 

 of which has been determined by exact experiments, does not prove 

 that it is true for all. And it is known that there are wide differ- 

 ences in the resisting power both of the spores of different species 

 and in the vegetating cells. To admit that the tubercle bacillus or 

 the typhoid bacillus, etc., may form spores which have no greater 



