‘BACILLI IN 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 temperature 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 alower 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 60°, 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 ina 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 ard many others, the thermal death-point 
of which has been determined by exact experiments, does not prove 
that itis true for all. Anditis 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 
