64 SCIENCE PROGRESS 



ceedingly probable that in separating, admittedly roughly, the 

 oxidising enzyme, a certain quantity of reductase was present 

 along with the oxidase and added haemoglobin. The reductase 

 would reduce the oxyhemoglobin activating the oxygen which, 

 under the influence of the oxidase, oxidised the acid as reported. 

 This explanation at least accounts for the phenomenon observed 

 and especially for the fact that the haemoglobin alone had no 

 influence. 



In his recent text-book of Physiology, Professor Starling 1 

 writes : "There is no doubt that reducing substances are found 

 under normal circumstances in the tissues . . . and it is possible 

 that such reducing substances may aid in activating oxygen and 

 in the induction of certain oxidative processes." The italics are 

 ours, for this precisely expresses our belief that the chief reducing 

 substance in fresh normal tissues is an enzyme which does 

 originate or induce the oxidative tissue activities. This was 

 indeed Hoppe-Seyler's original suggestion ; all our work is in 

 the direction of confirming it. 



The source of active oxygen, as is well known, has been 

 referred to intracellular peroxides, of which an inorganic example 

 is hydrogen peroxide. Now it is remarkable that most tissue 

 juices contain the enzyme catalase whose duty would seem to 

 be to decompose hydrogen peroxide into water and molecular 

 oxygen thus — 



2H.,0 2 = 2(H 2 0) + 2 . 



But that catalase is not responsible for the reductions we have 

 been studying we have detailed evidence. A peroxidase has 

 been postulated as responsible for the decomposition of hydrogen 

 peroxide which yields the active oxj'gen thus — 



H 2 2 = H 2 + O,. 



Whatever, then, the peroxidase is, it is virtually a reducing 

 agent. We are not prepared to explain the relationship of 

 reductase to peroxidase or to the hypothetical peroxides, but 

 we'prefer to conceive of the inspiratory phase of tissue respira- 

 tion as the removal of oxygen from cell lymph and, therefore, 

 ultimately from oxyhemoglobin by the activity of a reducing 

 endo-enzyme. We find in tissues an enzymic reducer ; it reduces 



1 P. 1236. 



