IV 



YEAST 123 



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 the changes which it effects in 

 sugar, how are they to be accounted for ? Before 

 modern chemistry had come into existence, Stahl, 

 stumbling, with the stride of genius, upon the con- 

 ception 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, com- 

 municated that motion to the sugar, and thus 

 caused its resolution into new substances. And 

 Lavoisier, as we have seen, adopts substantiaUy 

 the same view. But Fabroni, 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, pro- 

 duces a new substance analogous to opium. This 

 is decomposed by distillation, and gives rise to 

 alcohol. Next, in 1803, Thenard propounded a 

 hypothesis which partakes somewhat of the nature 

 of both Stahl's and Fabroni's views. " I do not 

 believe with Lavoisier," he suvs, " that all the 



