VIRULENT DISEASES. 193 



hypotheses, they allowed themselves to be deceived by 

 false assimilations to facts of a purely chemical kind, 

 which appeared to them to be connected with the phe- 

 nomena of fermentation and virulence. 



Liebig wrote, ' By the contact of the virus of small- 

 pox the blood undergoes an alteration, in consequence 

 of which its elements reproduce the virus, and this 

 metamorphosis is not arrested until after the complete 

 transformation of all the globules capable of decompo- 

 sition.' 



This vague theory of viruses was forced to give 

 way before the multiplied experiments of Pasteur. 

 But before occupying himself with further discoveries, 

 although it had been irrefutably proved that the 

 microscopic parasite was the true contagium, it was 

 necessary to throw light upon the facts, mainly accu- 

 rate, which had been announced by Jaillard and 

 Leplat, and to bring them into harmony with the facts, 

 not less certain, which had been advanced by Davaine. 

 The rabbits which Jaillard and Leplat had inoculated 

 with a drop of the blood of a cow or sheep stricken 

 with splenic fever, died rapidly, and the blood of these 

 rabbits was shown to be also virulent. It was suffi- 

 cient to inoculate other rabbits with a very minute 

 quantity to cause their death. But Jaillard and 

 Leplat affirmed that the examination of that blood did 

 not reveal the existence of any microscopic organisms. 

 Paul Bert, on his part, had succeeded in destroying 



