THEORY OF ACTION OF OXIDASES 535 



an "oxidizing-ferment" and to give expression to the happy 

 thought that there occur in the body readily oxidizable sub- 

 stances ("autoxidizable") which have the power of trans- 

 ferring the oxygen in active form to substances which are 

 oxidizable with difficulty ( ' ' dysoxidizable " ) , such as the nutri- 

 ent materials. On this as a foundation Engler and Bach later 

 built up, with their associates, their peroxide theory. In 

 this theory it is supposed that the oxygen attaches itself to 



O 

 the autoxidizable substances in the form I and produces 



addition-products of the type R<l (moloxide) or of the 



R O 



I . As a special instance of such peroxide formation 

 R o 



the production of hydrogen peroxide may serve, zinc in the 

 presence of water and oxygen being regarded as exerting 



OH.H 

 an oxidizing action : Zn + + 2 = Zn (OH) 2 + H 2 O 2 . Accord- 



OH.H 



ing to Engler and Herzog oxidations of this type may be 

 represented by the following schema : A + 2 = A0 2 , or 

 again in the sense of an equivalence, A + 2 ;^:A0 2 (as, for 

 example, haemoglobin, oxygen and oxyhaemoglobin). A 

 second, not an autoxidizable substance, B (" acceptor ") 

 can be oxidized by AO 2 in the sense : A0 2 + B = AO + BO. 

 By analogous process we may, for example, explain why 

 indigo is not attacked by molecular oxygen, although, if an 

 indigo solution is shaken up with benzaldehyde, both sub- 

 stances become oxidized. The benzaldehyde is transformed, 

 presumably under the influence of the atmospheric oxygen, 



. , /CeHi.COH + O, = CH 6 .CO.O\ 



into benzoyl-hydrogen peroxide ( I J, 



V H.6/ 



and this then (with formation of benzoic acid, C 6 H 5 .COOH) 

 acts as an oxidizing agent upon the indigo. 



But to return to the above schema, AO (the oxide of the 

 autoxydator) is capable of oxidizing another molecule of B, 



