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within the economy becomes gradually strengthened. It 

 becomes by degrees able to kill guinea-pigs three or four days 

 old, then a week, a month, some years old, then sheep them- 

 selves ; the bacteridium has returned to its original virulence. 

 We may affirm , without hesitation , though we have not had the 

 opportunity of testing the fact, that it would be capable of 

 killing cows and horses ; and it preserves that virulence inde- 

 finitely if nothing is done to attenuate it again. 



"As to the microbe of chicken-cholera, when it has lost its 

 power of action on hens, its virulence may be restored to it by 

 applying it to small birds such as sparrows or canaries, which 

 it kills immediately. Then by successive passages through the 

 bodies of those animals, it gradually assumes again a virulence 

 capable of manifesting itself anew on adult hens. 



" Need I add, that, during that return to virulence, by the 



way, virus-vaccines can be prepared at every degree of virulence 



for the bacillus anthracis and for the chicken-cholera microbe. 



This question of the return to virulence is of the greatest 



interest for the etiology of contagious diseases." 



Since charbon does not recur, said Pasteur in the course of 

 that communication, each of the charbon microbes attenuated 

 in the laboratory constitutes a vaccine for the superior microbe. 

 " What therefore is easier than to find in those successive virus, 

 virus capable of giving splenic fever to sheep, cows and horses, 

 without making them perish, and assuring them of ulterior 

 immunity from the deadly disease? We have practised that 

 operation on sheep with the greatest success. When the season 

 comes for sheep-folding in the Beauce, we will try to apply it 

 on a large scale." 



The means of doing this were given to Pasteur before long ; 

 assistance was offered to him by various people for various 

 reasons ; some desired to see a brilliant demonstration of the 

 truth ; others whispered their hopes of a signal failure. The 

 promoter of one very large experiment was a Melun veterinary 

 surgeon, M. Kossignol. 



In the Veterinary Press, of which M. Eossignol was one 

 of the editors, an article by him might have been read on the 

 31st January, 1881, less than a month before that great dis- 

 covery on charbon vaccine, wherein he expressed himself as 

 follows : ' ' Will you have some microbe ? There is some 

 everywhere. Microbiolatry is the fashion, it reigns undis- 

 puted; it is a doctrine which must not even be discussed, 



