ROLE OF REDUCTASE IN TISSUE RESPIRATION 57 



to be the case, for we had unmistakable evidences of its activity 

 in tissue juices both from the frog and from the fish. A speci- 

 men of liver juice from the fish, which at room temperature 

 reduced oxyhemoglobin in seven minutes, reduced it at 40°C. 

 in two minutes. We found reductase, in fact, in four out of the 

 five great groups of the Vertebrata — mammals, birds, amphibia, 

 and fishes. The reductase from fish's liver was amongst the 

 most energetic of any we encountered. The reason seems clear : 

 the fish has access to so little oxygen that its organs must be 

 able to extract it very thoroughly. 



The marked acceleration of reduction at temperatures above 

 40 C. is in accordance with what we know as to the intensifica- 

 tion of respiratory tissue changes in fever. The late Christian 

 Herter, of New York, has told us that in hog-cholera the reduc- 

 tion processes are exaggerated. 



We had no evidence that reductase was qualitatively different 

 in the various organs of the same animal nor in the different 

 kinds of animal examined. There is no specificity of reductase 

 from any one source in reference to haemoglobin from any 

 other. Thus the cat's liver juice can reduce the blood of any 

 other mammal, or of a bird, a frog, or a fish. The reductase of 

 a bird can reduce the blood of a mammal, a frog, or a fish, and 

 so on. We have called these " crossed reductions " ; they prove 

 there is no mutual specificity of relationship between the 

 enzyme and the pigment. Incidentally they corroborate the 

 belief that the resemblances between the haemoglobins from 

 various animals are more numerous than the differences. The 

 physiological significance of the absence of any specificity 

 between reductase and haemoglobin is that foreign blood intro- 

 duced into any animal can still be reduced by that animal, so 

 that, for instance, human tissues can obtain oxygen from the 

 haemoglobin of any lower animal. The danger to the human 

 being as regards blood-transfusion is not that the foreign blood 

 will not be reduced, but that it may act haemolytically toward 

 the red corpuscles of the receiver. 



The object of the tissue reduction of oxyhaemoglobin is 

 virtually to cause the oxygen to dissociate from the pigment; 

 so that all work on the subject of the dissociation of oxyhaemo- 

 globin has a bearing on the present problem. Some workers 

 have laid stress on rise of temperature as a factor in this 

 dissociation. Where this factor is operative, it is a vastly 



