74 THE LIFE OF PASTEUR 



of preparing laevo-tartaric acid. Why does the dextro-tartaric 

 acid alone become putrefied? Because the ferments of that 

 fermentation feed more easily on the right than on the left 

 molecules." 



' I have done yet more," he said much later, in a last lecture 

 to the Chemical Society of Paris ; " I have kept alive some little 

 seeds of penicillium glaucum — that mucor which is to be found 

 everywhere — on the surface of ashes and paratartaric acid 

 and I have seen the laevo-tartaric acid appear ..." 



What seemed to him startling in those two experiments was 

 to find molecular dissymmetry appear as a modifying agent 

 on chemical affinities in a phenomenon of the physiological 

 order. 



By an interesting coincidence it was at the very moment 

 when his studies were bringing him towards fermentations 

 that he was called to a country where the local industry was 

 to be the strongest stimulant to his new researches. 



