BACTERIAL RESPIRATION 193 



and the uxidatiun of ethyl alcohol to acetaldehyde : — 



/" 



C'Hj.C^— OH y r'Hjf'HO ^ If. 



The hydrogen atoms shown in bold type are those trans- 

 ferred. In cases where there is an actual increase of 

 oxygen in the oxidised molecule, he regards the first step 

 as being the formation of a hydrate, the second step 

 being the loss of hydrogen from the hydrate. Thus the 

 oxidation of acetaldehyde to acetic acid is considered to 

 follow the equation : — 



CH3C— H ^ HoO > CH3C;— H > CH3C— OH -r Ho 



\0H 



(acetaldehydf) (acetaldehyde (acetic acid) 



hydrate) 



Lactic acid and glucose were found to be oxidised in a 

 similar way by these metallic catalysts, especially if a 

 hydrogen acceptor such as oxygen or some easily reduced 

 compound was added. Methylene blue proved a very 

 useful hydrogen acceptor. 



Wieland regards biological oxidations as being similar 

 in character, the difference being that the metallic catalyst 

 is replaced by an enzyme. The enzymes are variously 

 known as a reductase when the hydrogen acceptor is a 

 dye or a nitrate or some similar compound, as a mutase 

 when the acceptor is a second molecule of the substance 

 being oxidised (as, for example, when acetaldehyde is 

 converted into acetic acid and alcohol by the acetic acid 

 bacteria), or as an oxidase when atmospheric oxygen is 

 activated as the hydrogen acceptor. 



That bacteria are able to activate a large variety of 

 compounds in this way has been shown by the use of 

 the " methylene blue technique." In this procedure a 

 washed suspension of the organism under investigation 



