136 THE ROYAL SOCIETY OF CANADA 



on oxidase has to make due allowance for the presence of reducing 

 substances. 



Dr. Vernon and also Prof. B. Moore -'" have pointed out several 

 respects in which oxidase differs from reductase. 



It is perhaps too soon to formulate any theor}^ of tissue-respiration; 

 but when the scheme is outlined it must be one taking cognisance of all 

 three respiratory types of enzymes and not a scheme framed in terms 

 of oxidase alone. 



Pi'ovisionalh'. one might say that by reductase oxygen is abstracted 

 from oxy haemoglobin and bi-ought within the sphere of the activity 

 of the oxidase which applies it to the oxidation of the carbon, hydrogen, 

 sulphur, phosphorus, etc., in, or in the neighbourhood of, the living 

 protoplasm. 



With regard to hœmoglobin, I have direct evidence that liver- 

 juice can reduce this pigment from the fully oxidised tw^o-banded 

 condition to the fully reduced one-banded within three hours at 41°C. 

 The c|uantities used were a test-tubeful of solution of oxyhœmoglolDin 

 from freshly drawn defibrinated rabbit's blood, and three grammes of 

 freshly disintegrated liver squeezed before the animal heat had left 

 it. This mixture was shaken up from time to time to distribute the 

 juice, and within a minute or two, the solution had begun to lose its 

 brightness which it steadily continued to do. The two bands in the 

 spectrum l^ecame progressively hazier, until at the end of three hours 

 they had disappeared and been replaced by the single band of hiemo- 

 globin; shaking this pigment at once made the two bands re-appear; 

 it was, therefore reduced, but still oxidisable. 



A contî-ol, similar in all respects except that the juice was boiled 

 for five minutes, showed no signs of being reduced at the end of 72 

 hours, a period twenty-four times as long. This solution never did 

 become reduced, but passed normally into the state of methœmoglobin. 



A period of three hours may seem a long one in which to have 

 to wait for reduction to hœmoglobin; but we must remember that in 

 vitro we have the entire mass of the solution finally fully reduced, 

 while in vivo we never have the oxyhsemoglobin fully reduced in con- 

 secjuence of contact with the living tissues during only one transit of 

 the blood. The blood is only fully reduced after the many transits 

 of asphyxia. 



I think, then, that we are fully justified in regarding the reductase 

 as the respiratory ferment of the living tissues, the endo-enzyme 

 through whose reducing power oxygen is split off from the oxyhœmo- 

 glo])in in the several capillary districts. 



It would seem to be the ferment which starts the process of in- 

 ternal respiration, oxidase that which continues and completes it. 



