IN ANIMAL TISSUEvS. HARRIS. 273 



The presence of an oxidase, more probably of oxidases, 

 must be remembered when one is working with the reducing 

 ferment. As Dr. Vernon has shown, there are oxidases in the 

 liver which must of necessity work in the direction opposite to 

 that taken by the reductase. 



Hence when we obtain a less distinct reduction than we 

 expect, we have to remember that the oxidase may have 

 been active. We have, in fact, the converse of the difficulty to 

 which Dr. Vernon(^*) alluded when, investigating "The 

 quantitative estimation of the indophenol oxidase of animal 

 tissues", he wrote: "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 ab- 

 sence of an oxidizing 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." 



At an earlj' stage I had noticed that in a tube in which the 

 Prussian blue, had been completely reduced to the leuco state, 

 a le-establishing of the colour was evident from about the end of 

 the first week onwards. A mixture of fresh liver-juice shaken 

 up with pigment of suitable strength would begin to become 

 blue again in spite of the fact that the mixture was covered by 

 a laj'er either of toluene or of oil to the depth of an inch. 



In the routine observations, I made no attempt to elimin- 

 ate the oxidase of press juice, but in one experiment Dr. 

 Lovatt Evans and I definitely arranged to exclude the physiol- 

 ogical activity of that ferment. Accordingly we kept a sealed 

 up mixture of liver-juice and Prussian blue at room tempera- 

 ture under an atmosphere of pure hydrogen in a completely 

 reduced state for three and a half months. It never showed 

 the slightest re-blueing: on breaking open the tube and 

 adding H2O2 the contents immediately became bright blue. 

 Exposure to the air produced the same result more slowly. 

 Evidently the activity of the oxidase was prevented expressing 

 itself owing to there being no oxygen for it to deal with. 



