56 SCIENCE PROGRESS 



action of reductase on various pigments and other salts capable 

 of reduction may be, we have to remember that none of them 

 is even approximately the natural medium of the tissues, and 

 most of them are distinctly toxic for the living substance. 

 Nothing other than oxyhaemoglobin is the natural substance 

 yielding the oxygen dealt with by tissue reductase. We have 

 recently, therefore, made a systematic investigation into the 

 relationships of reductase and oxyhaemoglobin in solution, a 

 research which has brought to light many fresh data. The 

 method used was spectroscopic : that is the change from the 

 two-banded spectrum of oxyhaemoglobin to the one-banded 

 spectrum of fully reduced haemoglobin was followed with a 

 direct-vision spectroscope. There were two advantages in this 

 method : the first that the reductase was acting in its own 

 proper substrate, as it were, the respiratory pigment oxy- 

 haemoglobin ; the second that the end-point was as accurate as 

 could be obtained in a spectroscopic method. The personal 

 factor was practically eliminated. As the mixture of juice and 

 diluted blood was examined from moment to moment, the two 

 bands were seen gradually to fade away and be replaced by the 

 single fainter band of the reduced pigment. The change of 

 colour seen by the naked eye was observed to correspond very 

 closely with the spectroscopic appearances. The fresh mixture 

 of tissue juice and oxyhaemoglobin was of course pink, but as 

 reduction proceeded it became of a duller red until finally, when 

 fully reduced, it was of the purple or livid colour so characteristic 

 of venous blood. Towards the end of our work we were able 

 to say even by inspection when a specimen was fully reduced ; 

 the spectroscope almost always corroborated us. We found 

 that the fresh liver juice (cat) in presence of an aqueous solution 

 of oxyhaemoglobin (cat's blood diluted one in twenty-five) would 

 completely reduce the pigment at 40 °C. within five to six 

 minutes. At room temperature (i7-2o°C.) the time was 

 approximately four times as long. The acceleration in the rate 

 of the reduction of blood pigment with rise of temperature was 

 particularly instructive with fresh juice ; the times of reduction 

 were 36 minutes at io°, 22 at 20 , 10 at 30 , 5 at40°, 2*5 at 50 , 

 and 175 at 55°C. 



Since reductase thus can work through a large range of 

 temperatures, we might expect that it would be found both in 

 cold-blooded and in warm-blooded animals. This we discovered 



