[HARRIS] A REDUCING ENDO-ENZYME 131 



Hence only the earlier portions of liquids emerging from perfused 

 organs, or being secreted into the gall-bladder or ureter, should be 

 examined for reduced material. Because a kidney, perfused indef- 

 initely long with ferric chloride, does not continue to produce unlimited 

 quantities of ferrous chloride is no evidence that it was not originally 

 able to reduce some of it, for such substances, even in dilute solution, 

 are more or less toxic to living protoplasm, especially in experiments 

 in which the protoplasm is receiving no blood at all. 



(c) The last criticism is that of A. Heffter^^, which is directed not 

 so much against the methods of judging of reduction by the fading of 

 pigments as against the whole conception of tissue-reduction being en- 

 zymic in nature. Heffter holds that the labile H of colloids in such a 

 grouping as cysteine is able to effect all the reductions observed. He 

 says that crystallised egg-albumen can bring about many reductions. 

 Heffter's contention is that proteins apart from life can actively reduce. 



Confining ourselves first of all to Prussian blue, it is certain that all 

 proteins do not cause this pigment to fade, at least within times meas- 

 ured by hours. For one thing, gelatine itself even without acid, does not 

 cause soluble Prussian blue to fade even before it is injected into an 

 organ. 



It is well known that this injection-mass mixed with the blood- 

 proteins in the large vessels of mammals at body temperature is not re- 

 duced or caused to fade. Neither is methylene blue; those pigments 

 remaining blue produce along with the red of the blood a purple colour. 

 If Heffter be correct we should expect the blood-proteins to reduce 

 these pigments to a pale green or leuco condition; this they certainly 

 do not do. 



If one mixes a saline solution of pure serum-albumen or serume 

 globulin with Prussian blue, no fading takes place at room temperatur- 

 within 24 hours. 



In 1912 my co-worker at that time Dr. H. J. M. Creighton^®, of the 

 Dalhousie University, Halifax, N. S., investigated this subject with 

 very great care, and published his results in the Transactions of the 

 Nova Scotian Institute of Science. 



Dr. Creighton showed that if one mixes 10 c.c. of a 15% solution 

 of egg-white in dilute NaCl with 10 c.c. of a 0-05% solution of soluble 

 Prussian blue (Potassium ferric ferrocyanide) , and keeps the mixture at 

 60°C, the colour will have faded at the end of an hour. The fading is 

 gTadual. Dr. Creighton writes, "With pure white-of-egg at a high 

 temperature, the decoloration of the soluble Prussian blue was found to 

 proceed with greater rapidity". On the other hand, white-of-egg 

 solution and 0-05% Prussian blue, mixed and kept at room temperature, 

 showed no fading or change of colour at the end of six hours. 



