32 PASTEUR 



proved that tartrates and paratartrates were 

 the same identical salts, excepting that the 

 former acted upon polarised light and pos- 

 sessed a rotary power, while the latter remained 

 without action. It is at this precise point that 

 we are forced to admire the inspired intuition 

 of Pasteur, who, starting from a preconceived 

 idea, proved experimentally that it was correct. 

 Why was there this difference, he asked him- 

 self, between salts which appeared to be identi- 

 cal? Undoubtedly it was due to a difference in 

 their composition which had an influence upon 

 their external aspect, a difference which had 

 not yet been observed. And this difference he 

 discovered by a searching examination of these 

 crystals. The tartrates had one hemihedric 

 facet were manchots, one-armed, to borrow 

 M. Duclaux's vivid simile while the paratar- 

 trates obeyed the law of symmetry in regard to 

 their facets. The rotary power was directly re- 

 lated to the dissymmetry of the molecular 

 structure. This first discovery was followed by 

 a second, which was in a way a consequence of 



