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out causing disease, and that it had the property, when so inocu¬ 
lated, of protecting such animals from the effect of subsequent 
inoculations with virulent blood. It was believed that the bacilli 
were all destroyed at this temperature, and that the acquired im¬ 
munity resulted from the introduction of substances which had 
been formed by them. 
In this a fact and a theory were combined, and some of those 
who are so fond of criticising the germ theory seemed unable to 
comprehend where the one stopped and the other began; I think 
all were willing to accept the former, but some of us refused to 
believe the latter until better evidence was furnished. This was 
fortunate, for when M. Toussaint came to try his experiments on 
a larger scale, he was obliged to recall the theoretical part of his 
first statement. Twenty sheep were inoculated with the prepared 
virus at Alfort, of which four died of charbon, while all the re¬ 
mainder were sick of the same disease, but recovered. The heat, 
therefore, certainly reduced the activity of the virus, and caused 
it to produce a milder form of disease; but the immunity con¬ 
ferred was demonstrated to be the result of this mild form of the 
malady, and not to the introduction of an inconsiderable quantity 
of a chemical substance.* 
Pasteur’s latest researches. —Since the above was written, 
I have received the Comjites Rendus de V Academie des Sciences 
for February 28th, 1881, in which M. Pasteur communicates his 
latest researches in regard to the charbon virus. He had pre¬ 
viously discovered that the action of atmospheric oxygen for a 
number of months (five to eight), destroyed the organism found 
in the virulent liquid of fowl-cholera subjects, and that during this 
period the virulence became progressively w r eaker, causing a milder 
form of disease, until, towards the last, and while the organism 
still retained its vitality, its virulence was entirely lost. Charbon 
virus was then investigated in the light of these facts. It was 
evident that the effect of atmospheric oxygen must be tried upon 
the rods, for the spores were known to retain their virulence un¬ 
changed for years. To prevent the formation of spores, the cul¬ 
tivations were made at a temperature of 42° to 43° C., at which 
* Compten liendug, XCI, pp. 457-8. 
