138 RESPIRATION 



no oxidation is effected, whereas blood charcoal containing 

 iron was very active. Further, the activity of a pure charcoal 

 could be greatly increased by steeping it in an iron salt and 

 then heating to a red heat ; such an artificially produced carbon 

 was affected by narcotics in the same way as the blood charcoal. 

 Hydrocyanic acid was found to depress the oxidative activity 

 of the charcoal to a remarkable degree, due, in Warburg's 

 opinion, to its combining with the iron to form complex ferro- 

 cyanides ; the depression was, however, not of a permanent 

 nature, since the charcoal regains its original activity after 

 some time. Warburg's opinion is that the active surface of 

 a cell is to be regarded as a mosaic of areas, some rich and 

 some poor in iron ; the colloidal conditions being the same, 

 both areas equally adsorb dissolved constituents of the cell 

 sap, but metabolic changes only take place in those regions 

 where iron is present, for the addition of a small amount of 

 hydrocyanic acid brings the activity to an end owing to the 

 inactivation of the iron ; there is, however, no measurable 

 reduction in the amount of material adsorbed, since the iron 

 areas form but a small part of the entire surface. 



While this theory fits the facts fairly well as regards the 

 oxidation of amino acids, it is less satisfactory when applied to 

 the oxidation of carbohydrates, since the carbon model has 

 practically no action upon glucose and still less upon fructose, 

 although hexosephosphates are attacked, a fact of some interest 

 in connection with the significance of the hexosephosphates as 

 an intermediate stage of carbohydrate metabolism in general ; 

 furthermore, some substances such as oxalic or formic acids 

 which are oxidised with difficulty in the living cell are fairly 

 easily attacked by the carbon model. 



DEHYDRASE. 

 The underlying idea of Warburg's theory is that for oxi- 

 dation to take place atmospheric oxygen has to be activated 

 at some surface by iron, possibly by the formation of an 

 unstable peroxide which sets free active oxygen. A theory 

 entirely opposed to that of Warburg is that of Wieland * 



* Wieland : " Ber. deut. chem. Ges.," 1912, 45, 679, 2613 ; 1913, 46, 

 333'- 



