104 PHYSIOLOGY OF YEASTS 



This theory has the advantage of explaining the liberation of car- 

 bon dioxide and the accumulation of alcohol during asphyxia of a 

 plant deprived of oxygen. 



However, numerous objections, in spite of the illustrations which 

 have been presented, have been raised that alcohol is rarely a food for 

 the yeasts. The oxidation of alcohol by fungi is not able to be re- 

 garded as a rare occurrence. According to certain authors, alcohol 

 seems to be a waste product. 1 



Kostytschew 2 has noticed that when wheat grains are kept away 

 from air and finally placed in air, alcohol is produced during the fer- 

 mentation and not the oxide. Certain investigators have added to this 

 theory a modification which resolves some of the difficulties. Thus 

 Kostytschew, Boy en-Jensen, 3 and Blackmann 4 have admitted that 

 alcohol produced by fermentation is not oxidizable. Alcohol will 

 not be a normal product of respiration; it will form only when the 

 intermediary products of respiration escape the action of oxydases. 

 According to Boyen-Jensen and Blackmann the true intermediary 

 product will be dioxyacetone. Kusserow 5 considers alcoholic fermen- 

 tation in the light of incomplete respiration. With the exclusion of 

 air the yeast reduces the sugar to a diatomic alcohol which further 

 reduces to ethyl alcohol, carbon dioxide and hydrogen. 



Autophagy or Autolysis of Yeasts 



We should now investigate the curious phenomenon known as 

 autophagy or autolysis. When, in a fermentation, the quantity of 

 yeast is lower than 40 per cent by weight of the sugar, the fermenta- 

 tion stops immediately at the exhaustion of the sugar. But if, on the 

 contrary, the quantity of yeast is greater than 40 per cent of the sugar 

 by weight, the fermentation continues after the exhaustion of the sugar. 

 The yeast lives, then, on its own substances. It ferments the glyco- 

 gen which it has accumulated and accomplishes a sort of autodigestion. 



This phenomenon may be observed in a yeast undergoing inani- 



1 Maquenne, L. La respiration des plantes vertes. Rev. g. des Sciences, 

 19Q5. 16th year. No. 13. 



2 Kostytschew, S. Ueber ein Einfluss ergorgener Zuckerlosungen auf die 

 Atmung der Weizenkeime. Bioch. Zeitschr. 23, 1910. 



3 Boyen-Jensen, P. Die Zersetzung des Zuckers wahrend des Respiration Pro- 

 zesses. Ber. der deutschen Bot. Ges. 26, 1909. 



4 Blackmann, F. Assoc. Brit, pour 1'Av. des Sciences. Congres de Scheefield, 

 1910. 



6 Kusserow, R. Respiration and fermentation, two allied physiological proc- 

 esses. Brennerci und Pressehefefabrik, 44 (1912), 1-3; Chemical Abstracts, 7 

 (1913), 2237. 



