192 PASTEUR: THE HISTORY OF A MIND 



to do so with security, he had need of an equipment of 

 facts and ideas which he did not yet possess, and which 

 his opponents forced him to acquire. 



The most remarkable example I can cite in support of 

 what I wish to say comes from the discussion with 

 Trecul, who, renewing an opinion introduced into science 

 by Turpin and later supported by Bail, Berkeley, 

 Hoffmann, Hallier, admitted the transformation of 

 microscopic species, one into another. This was denying 

 the specificity of the germ established by the first 

 labors of Pasteur on fermentations, and Pasteur had 

 combatted this opinion, beginning in 1861 in the Bulletin 

 de la Societe philomathique. To comprehend what 

 obscurities this theory would have introduced into 

 microbian pathology, it is sufficient to recall that a 

 denial of the specificity of the germ would have contro- 

 verted the present day belief in the specificity of disease. 

 It was, therefore, important that it should be rooted out 

 of all minds. 



Unquestionably, it was not the demonstrations of 

 Bail, of Hoffmann, or even those of Trecul which could 

 give credit to this theory. All these eminent botanists 

 were poor experimenters, going out to meet sources of 

 error, not to bar the way, so to speak, but to open it up to ' 

 them. But favoring this idea of the mutability of 

 species was the doctrine of spontaneous generation, 

 which found in this mutability one of its arguments. 

 There were the new ideas introduced by Darwin and the 

 school of evolutionists. Finally, and this was more 

 grave, Pasteur himself, the greatest authorized exponent 

 of the opposite school, or rather of the experimental 

 method, rejected, in the name of experimentation, 

 the transformation of yeast into Penicillium glaucum, 

 but accepted that of the Mycoderma vini, or flowers of 

 wine, into an alcoholic ferment under certain conditions. 



