Protective vaccinations 469 



\^m ^^ ^^^ ^^®® ^^ *^® vaccinations against anthrax we pass to the 

 ^^■roup of viruses whose organised nature is well known and which 

 I^Kan be injected in pure culture grown on artificially prepared media. 

 ^Khis method constitutes one of Pasteur's most brilliant discoveries, 

 ^ftade in collaboration with Chamberland and Roux. Before they had 

 ^^und a satisfactory method of vaccinating against anthrax these 

 observers had to solve the problem in connection with a less com- 

 ^^fclicated and less difficult case. From the first, in his studies on 

 ^^athogenic micro-organisms, Pasteur had devoted his attention to 

 finding a means of communicating immunity against these parasites. 

 With the aid of Chamberland and Roux he was not long in discover- 

 ing a method by which it was possible to attenuate the virulence of 

 the micro-organism of fowl cholera and to vaccinate fowls against 

 this terrible disease by inoculating them with this attenuated 

 micro-organism. Guided by these results Pasteur, Chamberland and 

 Roux set to work to find the vaccine against anthrax ; they were soon 

 confronted by a serious obstacle in the formation of spores which 

 prevented the attenuation of the bacilli. This obstacle they overcame 

 by submitting cultures of the bacillus to a temperature of 42*5° C. 

 Under this condition spores do not develop, and the bacilli become 

 attenuated at the end of a longer or shorter period. Although in 

 possession of these attenuated viruses, it still needed very laborious 

 investigations to adapt them to the vaccination of various species of 

 animals susceptible to anthrax, especially sheep. In this they were 

 also successful, and in 1881, over 20 years ago, Pasteur and his collabo- 

 rators demonstrated the efficacy of their method on a large number 

 of animals. This demonstration was made at Pouilly-le-Fort before 

 a large commission. We may affirm that this celebrated experiment 

 opened a new path to science and to the practice of vaccination. 

 It was performed on 50 sheep, half of which were vaccinated twice 

 with twelve days' interval, the other 25 sheep serving as control 

 animals. Fourteen days after the vaccination by the second vaccine [492] 

 all the 50 sheep were subjected to a test inoculation of a very strong 

 anthrax virus. Two days later the vaccinated animals remained 

 unaffected, whilst the control animals had all succumbed to anthrax. 

 Similar experiments, undertaken in France, Hungary, Germany, 

 Russia and elsewhere, confirmed the efficacy of anthrax vaccinations 

 and led to their extension into all the countries where bacterial 

 anthrax was rife. From the year 1881 the method came into regular 

 use, and before the end of that year there had been vaccinated, in 



