72 E. J. STIEGLITZ 



with acid and ferrocyanide and ferric chloride, respectively. 

 Prussian blue was readily formed in both cyhnders of gelatin, 

 and the diffusion had proceeded to approximately the same depth 

 in each instance. From the physical standpoint, therefore, 

 there is no apparent cause for the difference in behavior dis- 

 cussed above. 



From a chemical point of view, it is at once apparent that the 

 ferrous iron has nothing to do with the actions of the salt, for it 

 is firmly bound in the complex ferrocyanide radical. That this 

 binding is firm and stable in the body is shown by the fact that 

 the salt is non-toxic. Were the complex ion split, the free 

 cyanide would be extremely poisonous. Neither can we lay to 

 the sodium ion the responsibility for such behavior, and there- 

 fore we must assume that some characteristic of the ferrocyanide 

 complex is the cause. 



Thus, as it was thought that the cyanide radical might be, at 

 least in part, responsible for this difference in behavior, potas- 

 sium thiocyanate, which gives a very delicate, intense (red) color 

 reaction with ferric chloride, was sutstituted (K62) . But, to our 

 surprise, no red color was detectable anywhere in the body ten 

 minutes after an intravenous injection. In further tests (K64) 

 it was found that the presence of either egg albumin or blood 

 serum prevents the formation of the red Fe(SCN)3 and even 

 decolorizes it after it has been formed. The action of the albu- 

 min was solely upon the thiocyanate, as the ferric chloride was 

 shown to be free and uncombined by the addition of a little 

 sodium ferrocyanide, which gave a liberal precipitate of Prussian 

 blue. The presence of the sulphur atom in the cyanide radical 

 made it so unstable that combination with protein resulted. 

 However, such combination does not free a cyanide group, for 

 the salt is non-toxic. Such a binding with proteins is not true 

 with the ferrocyanide. 



Two experiments, of the nature of those discussed under series 

 III, were carried out, using a corresponding dose of sodium ferro- 

 cyanide in place of the green ferric ammonium citrate for injec- 

 tion. • Charts and tables 5 and 6 give the results. 



