130 THE ROYAL SOCIETY OF CANADA 



None of the salts of the tissues, NaCl, KCl, NasCO.,, Cag 2(P0J, 

 NagPO^ in strengths under 1% solution added warm, singly or in any 

 kind of combination, caused any fading to the green or to the leuco 

 condition, whereas the subsequent addition of such a reducer as pyro- 

 gallol at once caused fading through green to white. 



When the gelatine and Prussian blue mixture is used to inject 

 organs still living, the pigments is reduced, as I believe, by the agency 

 of the living tissues; and some histologists, aware of this fading, at- 

 tribute it to "contact with the alkaline salts of the tissues." 



Thus Rawitz^" recommends that a little acetic acid be added to 

 the injection-mass to prevent the "fading" by alkaline tissues. 



Naturally, this criticism applies only to pigmentary substances, 

 and has no applicability to non-pigmentary salts used to demonstrate 

 bio-chemical reduction. 



(b) The next source of fallacy one must bear in mind is the pos- 

 sible putrefaction of the proteins of press-juice in specimens of juice 

 kept for more than a few days. 



Toluene was the antiseptic used for all press-juices; some kind of 

 antiseptic is absolutely necessary, although Battelli^^ has emphasised 

 the inhibitory effect of antiseptics on the enzymic and respiratory 

 powers of tissues. The antiseptic used had obviously to be one which 

 would not of itself bleach or reduce the pigments or other substances 

 and would not act as an activator or inhibitant of the enzyme. Sodium 

 fluoride and many other substances had to be rejected on some of 

 those grounds. Toluene apparently prevented putrefaction in the 

 press-juices used. Had the reductions in old juice (two to six weeks old) 

 been due to putrefactive or autolytic substances, then the reducing 

 power should have 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 7nore marked as time 

 went on. I had, however, positive evidence of the absence of putre- 

 factive 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 of clear, then, that the reductions studied were not 

 brought about by the products of putrefaction or autolysis. 



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 expect the living tissue 

 to reduce unlimited quantities of such substances whether pigmen- 

 tary or not. 



