IN ANINAL TISSUES. FRASER. 267 



steadily increased with the age of the juice. But exactly 

 the opposite was found, the longer the juice was kept under 

 toluene the less it reduced until after ten weeks or so it did not 

 reduce at all. But putrefaction would have been progressive, 

 and therefore reduction due to putrefaction would have been 

 more marked as time went on. I had, however, positive 

 evidence of the absence of putrefactive micro-organisms in a 

 specimen of liver juice three months under toluene, which was 

 examined for me by Dr. Sholto Douglas of the University of 

 Birmingham and pronounced sterile. 



It seems clear, then, that the reductions studied were 

 not brought about by the products of putrefaction or 

 autolysis. 



(c) As regards fallacies, another point to be remembered 

 is that the substances employed — Prussian blue, ferric chloride, 

 etc., are all more or less poisonous. We cannot, therefore, ex- 

 pect the living tissue to reduce unlimited quantities of such 

 substances whether pigmentary or not. 



Thus only the earlier portions of liquids emerging from 

 perfused organs or being excreted into the gall-bladder or 

 ureter should be examined for reduced material. Because a 

 kidney perfused indefinitely 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 

 that protoplasm is receiving no blood. 



(d) The last criticism is that of A. Heffter (") which is 

 directed not so much against the methods of judging of re- 

 duction by the fading of pigments, as against the whole 

 conception of tissue-reduction being enzymic 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 crystallized egg-albumen can bring about many reduc- 



