IlS PLANT RESPIRATION 



It must be taken into consideration that two experimentally 

 established important facts favor the Bach-Engler theory: I. 

 Formation of moloxides by the autoxidation of some organic 

 substances and, II. The activation of hydrogen peroxide 

 and various other peroxides by means of peroxidases. The 

 Wieland theory can explain some cases of oxygeri fixation only 

 questionably. For example, Wieland seeks to explain the 

 autoxidation of aldehyde to carboxylic acid at the expense of 

 the oxygen of water by means of the intermediate formation of 

 aldehyde hydrate: 



CH3— CHO + H2O = CH3— CH(0H).2 



CH3— CH(OH).,= CH3— COOH+ 2H 



2H + O = H2O. 



Wieland bases this explanation on the fact that acetic acid 

 bacteria oxidise ethyl alcohol to acetic acid in the absence of 

 oxygen by way of the intermediate stage of acetaldehyde if the 

 active hydrogen which is split off is taken up by methylene blue. 

 The first stage (oxidation of ethyl alcohol to acetaldehyde), in 

 the absence of oxygen, can be made intelligible only through an 

 activation of hydrogen : 



CH3— CH.OH = CH3— CHO + H + H. 



The second stage (oxidation of acetaldehyde to acetic acid) 

 is also, according to Wieland, to be traced to the fact that there 

 is first formed aldehyde hydrate which then, owing to the activa- 

 tion of hydrogen, splits off atomic hydrogen and changes to 

 acetic acid. Since no atmospheric oxygen was available under 

 his experimental conditions, Wieland claims that his explanation 

 of the formation of acetic acid is the only one possible. Not 

 only possible but more probable than the details of the reaction 



account for all the well-known oxidations in vivo, even to such reactions as 

 /3-oxidation. It places the emphasis on the material used rather than on an ill- 

 defined system of enzymes and enzyme action, and promises at least a partial 

 reconciliation between the views of Wieland and those of the opponents of his 

 theory. The catalytic or promoter action of iron or similar components of the 

 "oxidase" system is not precluded because some such an agent provides the field 

 of force which is thought to activate the substrate.— £</. 



