THE CHEMICAL PROCESSES IN PLANT RESPIRATION 135 



processes requires the existence of a regulatory principle, even 

 if the fermentation of sugar outside the living cells were not 

 actually conceivable. Such a regulation is hardly possible 

 without the cooperation of the protoplasm. 



Hence we find that at present it has not yet been possible to 

 represent alcoholic fermentation by a series of obvious coupled 

 reactions; our present knowledge is still insufficient. Perhaps 

 the solution of the question of the formation of the methyl 

 groups in alcoholic fermentation could furnish the key to the 

 solution of the problem of fermentation. Even now it is very 

 probable that in the first stages of the process of fermentation 

 there occurs a cleavage of the chain of six carbon atoms into 

 two molecules of three carbon atoms each. The author of this 

 book believes that he can assume that oxidising enzymes of 

 normal oxygen respiration are sympathetically affected by 

 these steps, and therefore before the origin of the methyl groups. 

 Disregarding the fact that in general compounds with only 

 oxidised carbon atoms are more susceptible to biological oxida- 

 tion, it is pertinent to consider the processes in animal respira- 

 tion. In the case of the higher animals, the anaerobic cleavage 

 of sugar appears to be essentially identical with lactic acid 

 fermentation. Yet we may suppose that this process forms the 

 preparatory step to oxygen respiration. Thus there is consumed 

 by oxidising enzymes a substance which is formed in the 

 course of anaerobic glycolysis previous to the formation of 

 lactic acid, and so before the separation of the process of 

 fermentation into alcoholic and lactic acid fermentation. A 

 connection of the respiration of animal tissues with yeast 

 fermentation is shown by the fact that in the former the 

 coenzymes of alcohohc fermentation play an important role^ 

 and the well-known hexose phosphate is formed in the first 

 phases of the respiratory process.^ 



6. THE SUPPOSED FORMATION OF ORGANIC ACIDS IN THE 



RESPIRATORY PROCESS 



From the above exposition it is evident that at present it is 

 undecided which intermediate products of fermentation func- 



' Meyerhof, O. lot. cil. 



- Embden und Laqueur. Z. f. physiol. Chera. 98: 181. 1916-17. 



