148 PLANT RESPIRATION 



was found that the respiratory metabolism could also be effected 

 by means of killed cells the question of a mechanism of the 

 combustion of sugar could arise. 



If we survey the known facts in the field of the chemical proc- 

 esses which take place in oxygen respiration, we come to the 

 conclusion that the experimental investigation is seeking abso- 

 lutely new goals in recent years. Previously the principal 

 object of research was merely the external side of respiration 

 (influence of various effects of poisons, the stages of develop- 

 ment, etc.). At present there is developing the real biochemis- 

 try of respiration which provisionally records only the isolated 

 results, yet the results already won allow the advancement of 

 a connected theory of respiration which can serve as a working 

 hypothesis for further studies. It is also evident now that the 

 further development of the chemistry of plant respiration is 

 closely bound with the chemical investigations of alcoholic 

 fermentation. In the first place, it would be of the greatest 

 importance to identify the compound which serves simulta- 

 neously as the intermediate product of oxygen respiration and 

 of alcoholic fermentation, which is therefore formed from sugar 

 through the participation of the enzymes of fermentation, and 

 is then burned to the end-products of respiration by means of 

 oxidising agents. The supposition is not precluded that the 

 oxidising enzymes attack different products of fermentation 

 although the most oxidisable substance really constitutes the 

 normal intermediate product of oxygen respiration. It has 

 already been pointed out that this substance probably contains 

 no methyl groups. 



In conclusion we shall further raise the question whether 

 there are any organisms of fermentation which do not respire 

 even with unrestricted aeration. That yeast with free access 

 to oxygen owes its working energy chiefly to the process of 

 oxygen respiration appears to be scarcely questionable accord- 

 ing to the studies of Kostychev and Eliasberg {loc. cit.). On 

 the whole, the conclusion would perhaps not be sustained that 

 organisms which produce alcoholic fermentation when oxygen 

 is excluded respire normally when oxygen is admitted. This is 

 not true for all fermentations. Unpublished studies by S. 



