ROLE OF REDUCTASE IN TISSUE RESPIRATION 53 



off (artificial bile), and in the fluid from the hepatic vein some 

 ferrous chloride was present. 



The activities of tissues may be studied in other ways than 

 injecting chemical substances into their vessels ; for instance, 

 the organs may be crushed in a juice-press until thoroughly 

 disintegrated, and the resulting juice mixed with some pigment 

 or other substance, the reduction of which is expected. By this 

 means the active reducing material is brought into a contact with 

 the reducible material which is very much more intimate than 

 when, for instance, masses of the organ are merely immersed in 

 the reducible solutions. By this technique press-juices of liver 

 and kidney of cat, sheep, rabbit, horse, and frog are able to 

 reduce methylene blue to methylene white, sodium indigo- 

 disulphonate to the colourless chromogen and sodium nitrate 

 to sodium nitrite. It was found also that, e.g. liver juice could 

 reduce the pigment methaemoglobin first to the stage of oxy- 

 haemoglobin and later to that of fully reduced haemoglobin. A 

 boiled control of these juices had no reducing power whatever. 



Two French workers, Abelous and Gerard, as long ago as 1899 

 had suggested that these reducing powers of tissues might be 

 due to the presence of a ferment to which they gave the rather 

 barbarous name " reductase." We shall later give reasons for 

 suggesting a more specific term for this tissue ferment. 



The work of one of us (D.F.H.) carried out in 1909-10 was 

 undertaken with a view to determine what was the evidence for 

 the existence of a reducing enzyme in tissue press-juice. The 

 results then obtained, taken in conjunction with others arrived 

 at more recently, have gone far to convince us that there is 

 a tissue ferment with reducing powers. We have no evidence 

 that this ferment differs qualitatively whether it is derived from 

 liver, kidney, or other gland. 



Some of the evidence for this conclusion may be summarised 

 as follows : 



In the first place, in a control experiment where the juice is 

 boiled, none of the reducible substances mentioned above is 

 reduced thereby. The temperature of boiling water, as is well 

 known, destroys the activity of all enzymes. 



In the next. place, the general behaviour of the juice according 

 as the temperature is raised or lowered is in agreement with the 

 behaviour of acknowledged enzymes. Thus at minus io* C. there 

 is no reduction of soluble Prussian blue by fresh liver juice, 



