490 Prof. D. F. Harris and Dr. H. J. M. Creighton. [May 10, 



by one of us* that soluble Prussian blue is readily reduced to a leuco- 

 compound by small quantities of press juice from liver and kidney. This 

 action has been confirmed and further studied in the present investigation. 



Some experiments carried out with the press juice prepared on March 27 

 are described below. 



Three cubic centimetres of the absolutely fresh press juice were shaken up 

 in a test-tube with 10 c.c. of O05-per-cent. solution of soluble Prussian blue 

 at room temperature. The blue colour began to disappear immediately, and 

 in less than a minute, after passing through light blue, light green, and 

 greenish-grey, the mixture became pure light grey in colour. When the 

 same volume of boiled press juice was used, no decrease in the intensity of 

 the blue colour of the solution was observed at the end of several hours. 

 The reducing activity of the juice was found to diminish rapidly with time. 

 With a mixture containing 3 c.c. of the press juice 24 hours old, and 10 c.c. 

 of - 05-per-cent. soluble Prussian blue solution, it was found that 10 minutes 

 elapsed before its colour became greenish-grey, and two hours before it 

 became completely grey ; and when the juice was four days old it was 

 necessary to allow the mixture to stand under toluene for seven or eight 

 hours in order to obtain a greenish-grey colour. On adding a few drops of 

 hydrogen peroxide to some of the light grey mixture, the blue colour was 

 immediately restored. The blue colour of the mixture was also slowly 

 re-established by allowing it to stand exposed to the air. This re-blueing 

 commenced at the surface of the mixture and slowly progressed downwards. 

 If the decolorised mixture was spread out in a thin layer on a watch glass, 

 the colour quickly returned. It has been found on allowing the Prussian 

 blue press juice mixtures to stand, that the fawn-coloured protein matter of 

 the juice usually settled to the bottom of the test-tube, and that a white 

 grey substance remained suspended above it. Some of this grey suspension 

 was pipetted off. It was found that it rapidly turned bluish-green on 

 exposure to the air or on being treated with hydrogen peroxide. This 

 blueing of the whitish grey suspended material supports the suggestion of 

 Harris and Irvinef that potassium ferrous ferrocyanide is formed when 

 soluble Prussian blue is acted upon by liver press juice. As has been 

 already mentioned, the colour of soluble Prussian blue, when mixed with 

 small quantities of press juice, gradually fades to a green grey, and after 

 further time has elapsed all trace of green colour disappears, leaving only 

 a pure grey. Further, it has been found that the first colour change takes 

 place more quickly than the second. This phenomenon suggests the forma- 

 * Harris, D. Fraser, loc. cit. 



t Harris, D. Fraser, and J. C. Irvine, ' Bio-Cliem. Journ.,' 1906, vol. 1, p. 357. 



