130 PLANT RESPIRATION 



5. HYPOTHESES AS TO THE NATURE OF THE OXIDISABLE 

 PRODUCTS OF FERMENTATION 



It has already been demonstrated that ethyl alcohol, the end 

 product of fermentation, is hardly to be considered an inter- 

 mediate product of respiration. Apparently, substances which 

 are formed as intermediates of alcoholic fermentation are oxi- 

 dised by the respiratory process and their oxidative cleavage 

 proceeds more easily than that of unchanged sugar. 



The chemical side of alcoholic fermentation is not yet fully 

 known and unmistakable advances in this field must first be 

 made, for one does not begin with the first but rather with the 

 last phases of fermentation. Kostychev^ has discovered in 

 fermenting sugar solution under the influence of zinc and 

 cadmium salts, an aggregation of acetaldehyde which severely 

 checks the reducing power of the enzymes of yeast. At the 

 same time he has proven that yeast can reduce considerable 

 amounts of acetaldehyde to ethyl alcohol.- From this condi- 

 tion Kostychev has concluded that the formation of acetalde- 

 hyde represents the next to the last phase in alcoholic fermen- 

 tation. An important confirmation of this view was furnished 

 by the sulphite method of preparing glycerine by yeast, which 

 was worked out by Connstein and Ludecke^ and patented in 

 1915. In the presence of a considerable amount of sodium 

 sulphite (which in acid reaction changes in part to the bisul- 

 phite) sugar is split by yeast not only into COo and alcohol but 

 also in part into CO2, acetaldehyde, and glycerine. The equa- 

 tion for the sulphite fermentation was established by Neuberg 

 and Hirsch:^ 



CeHioOe = CH.2OH— CHOH— CHoOH + CH3— CHO + COo. 



1 Kostytschew, S. Ber. d. chem. Ges. 45: 1289. 1912; Z. f. physiol. Chem. 79: 130. 

 1912; 83: 9,?- 1913; 85: 493. 1913; 111 : 126, 132. 1920. 



- Kostytschew, S. und E. Hubbenet. Z. f. physiol. Chem. 79: 359. 1912; Kostytschew, 

 S. Ibid. 85: 408. 1913; f/. also Kostytschew, S. /6i(/. 89 : 367. I9I4;92:402. I9i4;the 

 brief paper of Neuberg and Kerb (Z. f. Garungsphysiol. 1 : 114. 1912), which was published 

 before the comniunication of Kostytschew and Hubbenet, gave only negative results, yet 

 aldehyde ammoniac and not free acetaldehyde was used for the reduction experiments. 



' On this point cf. W. Connstein und K. Ludecke. Ber. d. chem. Ges. 52: 13S5. 1919; 

 Zerner, E. /67'<i. 53 : 325. 1920. 



* Neuberg, C. und J. Hirsch. Biochem. Z. 100: 304. 1919; Neuberg, C, J. Hirsch und 

 E. Reinfurth. Ibiil. 105: 307. 1920. 



