732 SCIENCE PROGRESS 



colourless gelatine which on irrigation with H 2 2 at once became 

 blue. 



Here the material excreted is produced trans-epithelially : it 

 must have traversed at least (i) the endothelium of the capillary 

 wall, and (2) the epithelium of some part of the uriniferous 

 tubule : these two tissues, or one of them, evidently being 

 sufficiently energetic in their reducing power to transform the 

 deep blue ferric to the colourless ferrous salt. 



In several experiments on the kidney, the gland was practi- 

 cally perfused rather than injected with the gelatine and Prussian 

 blue (diluted one-half with 75 per cent. NaCl) under pressures 

 varying from 100 to 300 mm. mercury ; and these demonstrated 

 in a very interesting way the toxicity of soluble Prussian blue 

 (used, as it was in these cases, in the absence of oxygen), as 

 well as the consequent inability of devitalised protoplasm to 

 effect the reduction of the same material which a few moments 

 before it had completely reduced. 



One experiment may be taken as typical on this point — 

 kidney of sheep : blood washed out of vessels by warm 75 

 NaCl ; blue gelatine injection through renal artery, begun at 

 3.46 p.m. (outflow from renal vein unobstructed): at 3.55 leuco 

 gelatine began to drip from the ureter (pressure in renal artery 

 250 mm. Hg) and continued to do so for fifteen minutes thereafter, 

 when the flow began to show a green hue and finally a green- 

 blue : epithelium was now devitalised and was reducing no 

 longer. 



In the liver and kidney the fully reduced or leuco compound 

 obtained (di-potassio-ferrous-ferrocyanide) is the result of intra 

 vitam reduction by the protoplasm of the hepatic and renal 

 epithelium respectively. The tissues are alkaline reducers ; 

 the alkaline salts of lymph and tissues furnish the alkaline 

 medium in which alone the reduction can take place. 



The change to green or white is, in the first place, not due 

 to putrefaction, for the tissues are not yet dead. [We had a 

 very instructive demonstration of putrefaction-reduction in a 

 tube of decomposing gelatine and Prussian blue in which the 

 lowest stratum was "leuco," the middle green, while that next 

 the air in the tube was blue.] The change of colour to green or 

 white is, in the next place, not due to the action of the salts of 

 the lymph or tissues — is not a mere "fading due to alkalinity 

 of tissues." No doubt strong solutions of the hydrates of the 



