Polytechnic Association. ■ 801 



fermentation in sugar, because it constantly produces, as an essential 

 part of its vital manifestations, some substance which acts upon the 

 sugar, just as the synaptase acts upon the amygdalin. Or it may be 

 that, without the formation of any such special substance, the phy- 

 sical condition of the living tissue of the yeast plant is sufficient to 

 effect that small disturbance of the equilibrium of the particles of the 

 sugar which Lavoisier thought sufficient to effect its decomposition. 



Platinum in a very fine state of division — known as platinum 

 black, or noir de platine — has 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 a celui du noir 

 de platine. Mais il est essential 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 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 decom- 

 posing 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, ou the one hand, by the Stahlian doctrine, supported by 

 Li ebig, according to which the atoms -of the sugar are shaken into 

 new combinations, either directly by the Tondcs, or indirectly by 

 some substance formed by them; and, on the other hand, by the 

 Thenardian doctrine, supported by Pasteur, according to which the 

 yeast plant assimilates part of the sugar, and, in so doing, disturbs 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 does not arise solely 

 from its bearing upon the theory of fermentation. So long ago as 

 1838, Turpin compared the Torulce to the ultimate elements of the 

 tissues of animals and plants: "Les organes elementaires de leurs 



* Etudes sur les Mycodermes, Coniptes-Rendus, liv., 1862. 



[Inst.] 51 



