84 CRITIQUES AND ADDRESSES. [iv. 



allied to the yeast plant, has a similar effect upon dilute 

 alcohol, causing it to absorb the oxygen of the air, and 

 become converted into vinegar ; and Liebig's eminent 

 opponent, Pasteur, who has done so much for the theory 

 and the practice of vinegar-making, himself suggests that 

 in this case 



" La cause du phenomena physique qui accompagne la vie de la 

 plante reside dans un 6tat physique propre, analogue a celui du noir 

 de platine. Mais il est essentiel de remarquer que cet 6tat physique 

 de la plante est etroitement lie avec la vie de cette plante." 1 



Now, if the vinegar plant gives rise to the oxidation 

 of alcohol, on account of its merely physical constitution, 

 it is at any rate possible that the physical constitution 

 of the yeast plant may exert a decomposing influence 



on sugar. 



But, without presuming to discuss a question which 

 leads us into the very arcana of chemistry, the present 

 state of speculation upon the modus operandi of the 

 yeast plant in producing fermentation is represented, on 

 the one hand, by the Stahlian doctrine, supported by 

 Liebig, according to which the atoms of the sugar are 

 shaken into new combinations, either directly by the 

 Torulce, or indirectly, by some substance formed by 

 them ; and, on the other hand, by the Thenardian doc- 

 trine, supported by Pasteur, according to which the yeast 

 plant assimilates part of the sugar, and, in so doing, dis- 

 turbs the rest, and determines its resolution into the 

 products of fermentation. Perhaps the two views are 

 not so much opposed as they seem at first sight to be. 



But the interest which -attaches to the influence of the 

 yeast plants upon the medium in which they live and 

 grow (Iocs not arise solely from its bearing upon the 

 theory of fermentation. So long ago as 1838, Turpin 

 compared the forulce to the ultimate elements of the 



" Etudes surles Mycodermes," Comptes-Rendus, liv., 1862. 



