IV 



YEAST 127 



the very singular property of causing alcohol to 

 change into acetic acid with great rapidity. The 

 vinegar plant, which is closely 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 phenomene physique qui accompagne la vie de 

 la plante reside dans un etat physique propre, analogue k celui 

 du noir de platine. Mais il est essentiel de remarquer que cet 

 etat physique de la plante est etroitement lie avec la vie de 

 cette plante." ^ 



Now, if the vinegar plant gives rise to the oxi- 

 dation of alcohol, on account of its merely phy- 

 sical 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 fermenta- 

 tion 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 ; 



* Mvdes mr Us Mycodfrmes, Comptcs-Rendus, liv., 1862. 



