ROLE OF REDUCTASE IN TISSUE RESPIRATION 51 



of what have been called oxidases, ferments believed to be con- 

 cerned in effecting oxidations of a large number of substances 

 inside the living cells. These workers in fact have studied the 

 expiratory phase of tissue respiration, the exact nature of the 

 oxidative process leading to the final formation of carbon 

 dioxide and water with the production of correlated intermediate 

 substances. 



Investigators of oxidases are continually meeting with 

 evidences of substances in the living tissues which appear to 

 be working in the direction opposite to that of oxidation. One 

 particular oxidase has the power of oxidising a-naphthol and 

 di-methyl-paraphenylene-diamine to indo-phenol-blue, and has 

 been studied by Vernon, who calls it " indophenol-oxidase." 

 Studying the quantitative estimation ot this oxidase, Vernon 

 encountered " the unavoidable presence of reducing substances 

 some of which are possibly enzymes or reductases which act in 

 direct antagonism to the oxidases and, under certain conditions, 

 entirely overpower them. Hence the absence of an oxidising 

 action cannot be held to indicate the absence of oxidase unless 

 the conditions are so chosen to give the oxidase the best possible 

 chance of exerting its activity." Now it is just these reducing 

 agents which, on the other hand, we have been studying for 

 some years past. In 1885 Paul Ehrlich published an elaborate 

 research into the reducing power of living organs whereby they 

 were able to reduce indo-phenol-blue to the leuco-compound 

 and alizarine blue to alizarine white. The pigments were 

 injected subcutaneously into living animals. Ehrlich found that 

 almost all organs examined reduced one or other of these 

 pigments, some organs with great energy, such as liver, fat, and 

 the gastric mucous membrane. He recognised that even when 

 he could not detect reduced pigment, that did not prove that 

 there had been no reduction, but only that oxidation had been 

 quantitatively greater. The title of Ehrlich's paper was " The 

 Oxygen-avidity of the Organism," for he recognised that it was 

 in virtue of the avidity for oxygen on the part of the tissues that 

 they were also able to reduce certain pigments to the colourless 

 or chromogenic condition. In other words, the oxygen-avidity 

 is one expression of reducing power. Ehrlich made no sugges- 

 tion that this power was due to a ferment. 



In 1896 one of us (D.F.H.) noticed that when an animal, still 

 alive though chloroformed, had been injected with the mixture 



