of the Process of Fermentation. 163 



mentescible substances which is distinctly greater tlian tlie 

 weight of the substance set in motion by the organism, the 

 organ, or the cells." 



Pasteur, who seems here to agree with my opinion (first ex- 

 pressed in the ' Botanische Zeitung ' for 1848) as to the vitality 

 and faculty of increase of cells [e. g. secretion-cells or embryonal 

 tissue-cells) which have become diseased by abnormal condi- 

 tions of nutrition, nevertheless, led astray by correctly ob- 

 served but erroneously interpreted facts, mistakes the nature 

 of a whole group of these pathologico-necrobiotic vital pro- 

 cesses. The observation that beer-yeast growing upon the 

 surface of a solution of sugar absorbs atmospheric oxygen, 

 and converts it into carbonic acid without producing alcohol, 

 whilst the same yeast when carried beneath the surface of 

 the fluid by shaking produces alcohol as well as carbonic acid, 

 has misled Pasteur to the assumption that oxygen regularly 

 suppresses alcoholic fermentation. 



Assuming that Pasteur's statement is correct, and that yeast 

 floating on the surface of a solution of sugar produces no 

 alcohol, this does not prove that oxygen in such small quan- 

 tities as the fluid dissolves prevents the formation of alcohol, 

 and that the submerged yeast does not come into contact with 

 oxygen. As fermentation is due to continuous regeneration 

 and increase of the yeast-cells, and for the production of cells 

 oxygen must necessarily lend its aid unless all our observa- 

 tions are at fault, Pasteur's proposition that oxygen uncondi- 

 tionally prevents alcoholic fermentation must need modification 

 as follows : — that the unobstiiicted action of the atmospheric 

 oxygen upon yeast-cells prejudices their property of furnishing 

 alcohol and carbonic acid as products of the assimilation of 

 grape-sugar, inasmuch as it induces the cuticularization of 

 the membrane of the yeast-cells (that is to say, its partial con- 

 version into a resinous, fatty substance). It is well known 

 that masses of yeast, after being dried in the air, furnish more 

 alcohol on distillation than fresh undried yeast ; and all sorts 

 of daily experiences with saccharine fruits and solutions seem 

 to stand in opposition to Pasteur's views. 



Recently Pasteur has been confirmed in his opinion formed 

 upon the observation of vegetating yeast by the analogous in- 

 terpretation of a second fact, likewise correctly recognized. 



Couverschel long ago (Poggend. Ann. xxii. 1831) ob- 

 served that ripe saccharine fruits, when kept in carbonic acid, 

 were apparently avcII preserved for a long time, but at last 

 passed into alcoholic fermentation with indications of decay. 

 Pasteur repeated this experiment, and found that ])lums, 

 grapes, melons, all acid fruits and many others, when ke])t in 



