Polytechnic Association. 799 



a Torula larger than T. cerevisice, from a Mucor, a mould allied to 

 Penicillium. 



It follows, therefore, that the Tondce, or organisms of yeast, are 

 veritable plants; and conclusive experiments have proved that the 

 power which causes the rearrangement of the molecules of the sugar 

 is intimately connected with the life and growth of the plant. In 

 fact, whatever arrests the vital activity of the plant also prevents it 

 from exciting fermentation. 



Such being the facts with regard to the nature of yeast, and of the 

 changes which it effects on sugar, how are they to be accounted for ? 

 Before modern chemistry had come into existence, Stahl, stumbling 

 with the stride of genius upon the conception which lies at the 

 bottom of all modern views of the process, put forward the notion 

 that the ferment, being in a state of internal motion, communicated 

 that motion to the sugar, and thus caused its resolution into new 

 substances. And Lavoisier, as we have seen, adopts substantially the 

 same view. But Fabroui, full of the then novel conception of acids 

 and bases and double decompositions, propounded the hypothesis that 

 sugar is an oxide with two bases, and the ferment a carbonate with 

 two bases ; that the carbon of the ferment unites with the oxygen of 

 the sugar, and gives rise to carbonic acid ; while the sugar, uniting 

 with the nitrogen of the ferment, produces a new substance analogous 

 to opium. This is decomposed by distillation, and gives rise to 

 alcohol. Next, in 1803, Th6nard propounded a hypothesis which 

 partakes somewhat of the nature of both Stahl's and Fabroni's views. 

 " I do not believe with Lavoisier," he says, " that all the carbonic acid 

 formed proceeds from the sugar. How, in that case, could we 

 conceive the action of the ferment on it? I think that the first 

 portions of the acid are due to a combination of the carbon of the 

 ferment with the oxygen of the sugar, and that it is by carrying off a 

 portion of oxygen from the last, that the ferment causes the fermenta- 

 tion to commence — the equilibrium between the principles of the 

 sugar being disturbed, they combine afresh to form carbonic acid 

 and alcohol." 



The three views here before us may be familiarly exemplified by 

 supposing the sugar to be a card-house. According to Stahl, the 

 ferment is somebody who knocks the table, and shakes the card-house 

 down ; according to Fabroni, the ferment takes out some cards, but 

 puts others in their places ; according to Thenard, the ferment simply 

 takes a card out of the bottom story, the result of which is that all 

 the others fall. 



