STUDIES ON FERMENTATION. 333 



media, in consequence of a circumstance whicli it may be 

 interesting to mention here. A person who was working in 

 our laboratory asserted that the success of our experiments 

 depended upon the impurity of the sugar-candy which we 

 employed, and that if this sugar had been pure — much purer 

 than was the ordinary, white, commercial sugar-candy, which 

 up to that time we had always used — the ferment could not have 

 multiplied. The persistent objections of our friend, and our 

 desire to convince him, caused us to repeat all our previous 

 experiments on the subject, using sugar of great purity, which 

 had been specially prepared for us, with the utmost care, by a 

 skilful confectioner, Seugnot. The result only confirmed our 

 former conclusions. Even this did not satisfy our obstinate 

 friend, who went to the trouble of preparing some pure sugar 

 for himself, in little crystals, by repeated crystallizations of 

 carefully-selected commercial sugar-candy ; he then repeated 

 our experiments himself. This time all his doubts were over- 

 come. It even happened that the fermentations with the 

 perfectly pure sugar instead of being slow were very active, 

 when compared with those which we had. conducted with the 

 commercial sugar-candy. 



We may here add a few words on the non-transformation of 

 yeast into pou'cillium glaiicum. 



If at any time during fermentation we pour oflf the ferment- 

 ing liquid, the deposit of yeast remaining in the vessel may 

 continue there, in contact with air, without our ever being able 

 to discover the least formation oi peniciUiuiii glaiicum in it. "We 

 may keep a current of pure air constantly passing through the 

 flask ; the experiment will give the same result. Nevertheless, 

 this is a medium peculiarly adapted to the development of this 

 mould, inasmuch as if we introduce merely a few spores of 

 penicilUum, an abundant vegetation of that growth will after- 

 wards appear on the deposit. The descriptions of Messrs. 

 Turpin, Hoffmann, and Trecul have, therefore, been based on 

 one of these illusions which we meet with so frequently in 

 microscopical observations. 



