264 EXISTENCE OF A REDUCING ENDO-ENZYME 



Various extracts of organs were made — aqueous, saline 

 and glycerol — but as their reducing power was considerably 

 weaker than that of press-juice, these were not extensively 

 used in examining the properties of reductase. 



Injection of the Prussian blue and gelatine mixture into 

 the blood-vessels of organs was not used on many occasions. 

 It was, however, originally by this method that my attention 

 was drawn to tissue reduction, as I suspected that the "fading" 

 of the mixture in the capillaries of the parenchyma of liver and 

 kidney was chemically of the nature of a reduction. This 

 does not constitute a convenient method owing to the liabil- 

 ity of the gelatine to "set" if the proper temperature is not 

 maintained. 



The revival of the blue colour in an injected and almost 

 colorless kidney or liver cut open and exposed to the air or to 

 the action of H2 O2, is striking when seen for the first time. 

 The vessels on the cut surface begin to show up like letters 

 written in "sympathetic" ink. 



It was by this method that I obtained an artificial, 

 gelatinous, leuco urine from the sheep's ureter: it became 

 blue on treatment with H2 O2. 



The method of injecting ferric chloride through the 

 portal system and examining both the hepatic emergent 

 fluid and the contents of the gall-bladder for ferrous chloride, 

 in both of which it was found, proved a satisfactory method. 



IV. Preparation of the Juice. 



The following may be taken as typical of the technique. A 

 liver removed from the animal (rabbit, cat, dog, pig) before 

 the heat has left it, is perfused through the portal vein with 

 tap water at 40° C or with 0.75% NaCl until the water from 

 the hepatic vein is colorless. The organ is then rapidly cut 

 into largish pieces from which a good deal of water is allowed 

 to drain away. The pieces are then cut up into much smaller 

 bits and forced into the juice-press in which they are crushed 



