PROTECTIVE INOCULATIONS. 273 



with the same blood defibrinated and subjected to 55 C. for ten minutes, 

 according- to Toussaiiit, 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 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 Toussaiut'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 (' bacte-ridies du char- 

 bon" 1 ). 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 r&cidive pas' 1 )." 



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 seance of February 28th, 1881 (with the collaboration 

 of Chamberland and Roux), entitled "De 1' attenuation des virus et 

 de leur retour a la virulence. " In this connection Pasteur announces 

 his discovery of the fact that when cultivated at a temperature of 42 

 to 43 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- 

 18 



