52 SCIENCE PROGRESS 



of gelatine and soluble Prussian blue (so much used by histolo- 

 gists for demonstrating microscopic blood-vessels), and had been 

 opened up immediately, such an organ as the liver, instead 

 of being blue, was colourless. On cutting up the liver and 

 exposing the portions to the air, the blue colour was observed 

 to be restored until one could see minute vessels which a moment 

 before were quite invisible. The restoration of blue colour was 

 very rapidly brought about by pouring hydrogen peroxide over 

 the colourless surfaces. The bleaching of the soluble Prussian 

 blue in the gelatine injection mass was attributed to reduction 

 of the blue potassium ferri-ferrocyanide to the colourless di- 

 potassium ferro-ferrocyanide ; in terms of physical chemistry, to 

 the removal of a positive ionic charge of electricity from the tri- 

 valent ferric-ion. Similar results were obtained on injecting the 

 vascular system of the surviving kidney. It then occurred to us 

 that if the kidney could reduce a pigment which was still in its 

 vessels, the organ, if injected under sufficient pressure, might be 

 constrained to excrete an artificial urine through the normal 

 channel of the ureter. We found it possible to effect this. On 

 injecting into the artery of a sheep's kidney the warm soluble 

 Prussian blue and gelatine mixture, we obtained from the 

 cannulated ureter a few drops of an absolutely colourless 

 substance — an artificial urine — which on being treated with 

 hydrogen peroxide at once became blue. The kidney had, then, 

 excreted some gelatine and reduced soluble Prussian blue, 

 proving that these substances had travelled from the blood 

 capillaries to the ureter and in their passing had been reduced 

 by the still living renal epithelium. But after a time we noticed 

 that the outflow from the ureter had become blue, the kidney 

 cells had become poisoned and so no longer able to carry on 

 their vital reduction. It is not to be supposed that the living 

 tissues can withstand for more than a certain time treatment 

 with substances which cannot be other than ultimately toxic for 

 them. In later experiments ferric chloride was used with both 

 the liver and kidney in order to determine whether a substance 

 devoid of oxygen could be reduced to the lower form — ferrous 

 chloride — on being perfused through surviving organs. From 

 the kidney we obtained an artificial urine which contained ferrous 

 chloride, and some ferrous chloride was present in the liquid 

 which emerged from the renal vein. Similar results were got 

 with the liver ; from its bile duct ferrous chloride was drawn 



