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he saw no more yeast and no more active alcoholic fermenta- 

 tion ; he had therefore formerly been the dupe of a delusion. 

 In his Studies on Beer Pasteur tells of his error and its rectifi- 

 cation : "At a time when ideas on the transformations of 

 species are so readily adopted, perhaps because they dispense 

 with rigorous experimentation, it is somewhat interesting to 

 consider that in the course of my researches on microscopic 

 plants in a state of purity I once had occasion to believe in the 

 transformation of one organism into another, the transforma- 

 tion of the mycoderma vini or cerevisiae into yeast, and that 

 this time I was in error ; I had not avoided the cause of illusion 

 which my confirmed confidence in the theory of germs had so 

 often led me to discover in the observations of others/' 



"The notion of species," writes M. Duclaux, who was nar- 

 rowly associated with those experiments, " was saved for the 

 present from the attacks directed against it, and it has not been 

 seriously contested since, at least not on that ground." 



Some failures are blessings in disguise. When discovering 

 his mistake, Pasteur directed his attention to a strange 

 phenomenon. We find in his book on beer a sort of labora- 

 tory diary the following details on his observation of the 

 growth of some mycoderma seed which he had just scattered 

 over some sweetened wine or beer- wort in small china saucers. 



" When the cells or articles of the mycoderma vini are in 

 full germinating and propagating activity in contact with air 

 on a sweetened substratum, they live at the expense of trlat 

 sugar and other subjacent materials absolutely like the animals 

 who also utilize the oxygen in the air while freeing carbonic 

 acid gas, consuming this and that, and correlatively increasing, 

 regenerating themselves and creating new materials. 



"Under those conditions not only does the mycoderma vini 

 form no alcohol appreciable by analysis, but if alcohol exists 

 in the subjacent liquid the mycoderma reduces it to water and 

 carbonic acid gas by the fixation of the oxygen in the air." 

 Pasteur, having submerged the mycoderma and studied it to 

 see how it would accommodate itself to the new conditions 

 offered to it, and whether it would die like an animal 

 asphyxiated by the sudden deprivation of oxygen, saw that life 

 was continued in the submerged cells, slow, difficult, of a short 

 duration, but undoubtedly life, and that this life was accom- 

 panied by alcoholic fermentation. This time fermentation was 

 due to the fungus itself. The mycoderma, originally an 



