IN ANIMAL TISSUES. HARRIS. 275 



gen, sulphur, phosphorus, etc., in, or in the neighbourhood 

 of, the living protoplasm. 



With regard to haemoglobin, I have direct evidence 

 that liver-juice can reduce this pigment from the fully oxidized 

 two-banded condition to the fully reduced one-banded within 

 a few minutes at 41C. The quantities used were a test-tube full 

 of solution of oxy-haemoglobin from freshly drawn defibrin- 

 ated rabbit's blood, and three grams of freshly disinte- 

 grated 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 became progressively hazier until at 

 within ten minutes they had disappeared and been re- 

 placed by the single band of haemoglobin; shaking this 

 pigment at once made the two bands re-appear; it was, 

 therefore, reduced but still oxidizable. 



A control, 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. This solution never did become 

 reduced, but passed normally into the state of methaem- 

 oglobin. 



A period of ten minutes may seem a long one in which to 

 have to wait for reduction to haemoglobin, but we must re- 

 member that in vitro we have the entire mass of the solution 

 finally fully reduced, while in vivo we never have the oxy- 

 haemoglobin fully reduced in consequence of contact with the 

 living tissues during only one transit of the blood. The blood 

 is fully reduced only after the many transits in asphyxia. 



I think, then, that we are justified in regarding the reduc- 

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

 enzyme, through whose reducing power oxygen is split off 

 from the oxyhaemoglobin in the several capillary districts 



PROC. & TRANS. N. S. INST. Sci., VOL. XIII. TRANS. 19. 



