AbstractOxidation was measured by oxygen consump‐tion in a Warburg apparatus, modified to main‐tain constant partial oxygen pressure by auto‐matic electrolytic generation of oxygen with automatic recording of the oxygen consumed.The decrease in rate of oxygen consumption on the lowering of partial oxygen pressure at at‐mospheric pressure was found to depend on a) the varying influence of the nonoxygen‐dependent and the oxygen‐dependent reactions of the prop‐agation which may vary with the conditions such as the reactivity of the substrate, the tem‐perature, and the pH value but which is not affected by light irradiation; b) the varying rate‐limiting effect of slow oxygen diffusion, depending on the ratio between the rate of oxidation and the rate of oxygen diffusion.