THE USE OF SOLUBLE PRUSSIAN BLUE 733 



alkalies cause a rapid " fading " of the Prussian blue and gelatine, 



but K'OH, NaOH, and NH 4 OH do not exist in the fluids of 



tissues. 



The following salts which are found in blood or lymph were 



investigated with a view to observe their action on the blue 



gelatine both individually and when more than one was present, 



viz. NaCl; KC1 ; Na 2 C0 3 ; Ca 3 (P0 4 ) 2 ; Na 3 P0 4 . The strength 



of solutions used was less than 1 per cent. None of them 



added alone to the blue gelatine caused the appearance of 



the green or * leuco stage : the subsequent addition of a little 



N . N 



— NaOH caused slow fading of the blue, whereas if — KOH 



was used instead, there was a rapid fading to the colourless 

 condition. 



The addition of hydroquinone or pyrogallol to a mixture of 

 Berlin blue gelatine and # any one of these salts produced a 

 change of colour first to blue-green and then to green which 

 was ultimately discharged, the white of the leuco stage being 

 rapidly masked by the brown colour assumed by these reducers. 



By subsequent treatment with H 2 2 , the leuco or the green 

 material can be brought back to the blue condition, i.e. the 

 potassio-ferric-ferrocyanide reconstituted. A mixture of all 

 these salts (in which there was some haziness probably due 

 to CaCo 3 being precipitated) caused a slow fading of the blue 

 colour not through a green stage ; this latter was, however, at 

 once produced by the addition of pyrogallol to such a mixture. 



Ringer's solution, 1 added warm, produced no change beyond 

 that due to a corresponding dilution : the subsequent addition 

 of pyrogallol caused the appearance of a blue-green which was 

 restored to the original blue by H 2 2 . Ringer's solution with 

 Na 2 C0 3 added produced no fading, but, as before, the addition 

 of pyrogallol at once caused the mixture to become green. 



I therefore conclude that the green or leuco salt (the di- 

 potassio-ferrous-ferrocyanide) is produced by the reducing 

 activity of the living protoplasm acting, like the pyrogallol or 

 hydroquinone in the above experiments, as a reducer in an 

 alkaline medium. 



Thus I do look upon the " failure " of histological pre- 

 parations injected with Berlin blue where the leuco ferrous 



1 75 per cent. NaCl saturated with calcic phosphate and with 2 c.c. KC1 added 

 for each 100 cc. 



47 



