ALCOHOLIC FERMENTATION 83 



to accumulate sufficient oxygen. Pasteur also repeated the experi- 

 ment by eliminating these two sources of oxygen. For this he inoc- 

 ulated a trace of the yeast taken at the end of a fermentation and which 

 had not been in contact with air, into a flask almost completely filled 

 with sugar solution which had been boiled. Under such conditions, 

 the fermentation was very slow. Pasteur made it endure three months. 

 At the end of this time, 45 grams of sugar had disappeared and only 

 0.255 gram of yeast had been formed. The yeast, then, did not 

 develop. Thus from these experiments one sees the weight of sugar 

 which a unit weight of yeast is able to decompose into alcohol and 

 carbonic acid and at the same time diminish the activity of life and 

 the power of reproduction. 



All of this demonstrates that fermentation is correlated with 

 anaerobic development and that it is more active when oxygen is 

 absent. In the presence of air, the yeast functions like a plant. 

 It is nourished, respires and multiples. When placed in a reduced 

 air supply, it gives up or suppresses almost completely its multi- 

 plication. From the alcoholic fermentation, it draws the energy 

 which it needs. Then, the scarcer the oxygen, the slower the multi- 

 plication. 



The experiments of one of Pasteur's students, Denys Cochin, 

 indicate that fermentation does not take place in the total absence 

 of oxygen. The yeasts are not strict anaerobic organisms but are 

 intermediate between the aerobes and anaerobes. It is necessary 

 for them to always have a little oxygen, and it may be said that every 

 yeast that does not receive a minimum supply of oxygen from its 

 ancestors or does not find it in the culture medium, will perish. 

 Oxygen seems to have a beneficial action on the cellular activity and 

 the secretion of enzymes. 



These results have been contradicted to show that fermentation 

 though favored by the absence of oxygen, is, moreover, accomplished 

 in the scarcity of air (Brefeld, Hansen, Wehmer), but any invali- 

 dation of Pasteur's results seems not to have been produced up to the 

 present time. More recently Palladine and Iraklionoff 1 have shown 

 that if a yeast is able to produce small quantities of alcohol, even 

 in the presence of air, it may be explained by assuming the presence 

 of peroxidases which reduce peroxides, freeing nascent oxygen which 

 may be active. 



1 Palladine, W., and Iraklionoff, P. La peroxydase et les pigments respira- 

 toires chez les plantes. Rev. gen. de Bot. 23. 1911. 



