262 PASTEUR: THE HISTORY OF A MIND 



Pasteur who believed he could never accumulate too 

 much proof in support of his opinion, was here not un- 

 mindful of the fact that the animate cause of certain 

 virulent diseases was still contested. He had a beautiful 

 argument to add to those which he had already given 

 on anthrax. He made it instantly in the same shrewd 

 way that he made an ingenious analysis. 



"We should search," he says, "for proof that apart 

 from our vibrio there is no independent virulence pecu- 

 liar to liquids or solids, that, in short, the vibrio is not 

 simply an epiphenomenon of the disease of which it 

 is the obligate associate" (I. c.). Here are two liquids 

 which are identical in the beginning, exposed to air for 

 the same length of time. One remains virulent, the 

 other does not. 



They continued originally and both still contain two 

 kinds of substances solids and fluids. To which does 

 the virulence belong? It is evident that the substances 

 in solution have remained the same in both cases. It 

 is not possible to imagine any action produced on them 

 by the air which would not be alike in both tubes. Only 

 the solids, and there are none except the vibrios, have 

 undergone a change, being converted into resistant spores 

 in one case, and harmless granules in the other. It 

 is, therefore, to these alone that the virulence must be 

 attributed. 



We have not finished. We have just demonstrated 

 that the spore is the resistant aerobic form of the anae- 

 robic vibrio. How does it return to the vibrio stage? 

 This is equivalent to asking, since the spore-form occurs 

 everywhere, under what circumstances does it again 

 become dangerous? We shall soon see with what bril- 

 liancy Pasteur answers 'this question. 



