198 PASTEUR: THE HISTORY OF A MIXD 



III 



ANAEROBIC LIFE OF AEROBIC SPECIES 



In exchange, Pasteur had the sorrow of seeing ruined 

 one of the arguments most favorable to his physiological 

 theory of fermentation. But he ought not to have been 

 slow to congratulate himself upon this slight check, 

 because behind the fallen argument there arose another 

 still more convincing, which the first had masked. It 

 sufficed him, in order to find it, to repeat with Mucor 

 mucedo the preceding experiments. 



Bail had announced in 1857 that this mucor which 

 lives the life of an aerobic plant, when in contact with 

 air, can, when submerged in the absence of air, produce 

 a very active alcoholic fermentation. 



There are found then in the liquid, instead of more or 

 less septate mycelial filaments which serve to some 

 extent as roots for this plant, chains of round or oblong 

 cells, which Bail had taken for the cells of yeast of beer. 

 Repeating these experiments under the pure-culture 

 conditions which we have described, Pasteur determined 

 that these affirmations were exactly true. Submerged 

 and in the absence of air, the mycelium of the fungus 

 becomes very much septate, being transformed into a 

 chain of cells; simultaneously bubbles of carbonic acid 

 are given off, and alcohol is present in the liquid. What 

 is the explanation of this? Is this mucor then an ex- 

 ception? Can it undergo transformation into yeast? 

 This was the opinion of Bail; but we shall soon see 

 how much was gained by going l)elow the surface of 

 this question. From this apparently insignificant fact, 

 Pasteur has evolved a whole theory of fermentation. 



In order to place these phenomena in their proper 

 light we shall suppose that Pasteur treated them as 



