224 LOUIS PASTEUR. 



juxtaposition with the great fact of vaccination for 

 small-pox, this weakened microbe, which does not 

 cause death, behaves like a real vaccine relatively to 

 the microbe which kills, producing a malady which 

 may be called benign, since it does not cause death, 

 but is a protection from the same malady in its more 

 deadly form. 



But for this enfeebled microbe to be a real vaccine, 

 comparable to that of cow-pox, must it not be fixed, so 

 to speak, in its own variety, so that there should be 

 no necessity for having recourse again to the pre- 

 paration from which it was originally derived ? 

 Jenner, when he had demonstrated that cow-pox 

 vaccination preserved from small- pox, feared for some 

 time that it would be always necessary to have 

 recourse to the cow to procure fresh vaccinating 

 matter. His true discovery consisted in establishing 

 that the cow-pox from the cow could be dispensed 

 with, and that inoculation could be performed from 

 arm to arm. Pasteur made his enfeebled microbe 

 pass from one cultivation to another. "What would it 

 become ? Would it resume its very active virulence, 

 or would it preserve its moderate virulence ? 



The virulence remained enfeebled and, we may say, 

 unchanged. This showed it to be a real vaccine. 

 Some veterinary surgeons and farmers, on the an- 

 nouncement of this discovery, applied to Pasteur for 

 a vaccine against the disease which was so disastrous 



