PROTECTIVE INOCULATIONS. 273 
with the same blood defibrinated and subjected to 55° C. for ten minutes, 
according to Toussaint, these sheep subsequently resist inoculations with 
anthrax blood. . . . The bacillus, according to Toussaint, deposits in the 
blood of animals in which it multiplies-a substance which may become its 
own vaccine. By filtration while cold in one case, by a temperature of 55°C, 
in the other, the bacillus is said to be removed or killed; so that the inocula- 
tion of filtered or heated blood introduces into the animal inoculated vac- 
cinal matter deprived of bacteria.” 
After thus stating Toussaint’s method and explanation Pasteur 
proceeds to raise objections against this method, the principal of 
which are that the anthrax bacillus is not killed by exposure to a tem- 
perature of 55° C. for ten minutes, and that inoculation with a virus 
prepared in this way would result in a considerable mortality among 
the animals inoculated, although those surviving the inoculation would 
be protected. . 
In a communication made to the French Academy of Sciences, 
September 27th, 1880, Pasteur gave an account of an experiment made 
July 14th, 1879, upon two cows, which in connection with a subsequent 
experiment, made August 6th, 1880, upon four cows, led him to the 
conclusion that a single attack of anthrax protects from subsequent 
attacks. He says in the paper referred to: 
‘On the 15th of September, 1880, two cows, A and C, which had been 
very ill as a result of the first inoculation, made August 6th, were reinoculated 
on the left side, that is to say, on the side opposite the first inoculation. We 
used five drops of culture of the bacillus of anthrax (‘bactéridies du char- 
bon’). The following days there was no perceptible cedema and no elevation 
of temperature in either cow. The question is then resolved : a single attack 
protects (‘le charbon ne récidive pas’).” 
The next important steps in the line of experimental research 
leading to protective inoculations in the disease under consideration 
were reported by Pasteur in his communication to the French Acad- 
emy made at the séance of February 28th, 1881 (with the collaboration 
of Chamberland and Roux), entitled “De l’atténuation des virus et 
de leur retour 3 la virulence.” In this connection Pasteur announces 
his discovery of the fact that when cultivated at a temperature of 42° 
to 48° C., the anthrax bacillus no longer forms spores and rapidly 
loses its virulence. He says: 
‘*As regards its virulence, the extraordinary fact has been ascertained that 
the bacillus is no longer virulent after it has been kept for eight days at a 
temperature of 42° to 43° C.; at least its cultures are inoffensive for the 
guinea-pig, the rabbit, and the sheep, three species of animals which are 
very susceptible to anthrax. We are able, then, not only to attenuate viru- ° 
lence, but to effect its complete extinction, by a simple method of cultivation. 
‘‘Before the extinction of its virulence the microbe of charbon passes 
through the intermediate degrees of attenuation, and, on the other hand, as 
happens also with the microbe of fowl cholera, each of these degrees of vir- 
1 
