MECHANISM OF RENAL SECRETION 71 



in the urine in abundance. Similar differences in behavior of 

 the two compounds of iron in the animal body were recorded by 

 Ranvier, as acknowledged by Miss Fitzgerald in her w^ork on the 

 secretion of hydrochloric acid by the gastric tubules (80). In 

 testing for ferrocyanide in the fresh tissues at autopsy, we found 

 that the salivary glands, stomach wall and gastric contents, the 

 liver and subcutaneous as well as retroperitoneal connective 

 tissue gave strong Prussian-blue reactions twenty minutes after 

 the injection. 



Such a diffuse and non-specific distribution is quite the oppo- 

 site of that of the ferric iron, which appeared in a granular form, 

 never in interstitial spaces and only intracellularly or in the 

 blood-vessel lumina. In the introduction to this paper we made 

 the statement that iron (ferric) was used because it is an ioniz- 

 able salt giving a delicate microchemical color reaction. It is 

 true that the salts employed are ionized when in aqueous solu- 

 tion, but when mixed with blood plasma the iron may become 

 colloidal, possibly as ferric hydroxide, or be in loose physical or 

 chemical combination with the serum proteins. That the latter 

 alternative is the case is indicated by the particulate, granular 

 nature of the intracellular Prussian blue, by the absence of 

 a diffuse iron reaction in the interstitial tissues, and by the 

 presence of the retained iron in the phagocytic cells of the liver 

 and spleen, known to take up particulate matter (51, 52). 

 Furthermore, the marked effect of the iron upon cytoplasmic 

 physiology points toward some form of binding between the 

 iron and the tissue colloids. Realizing this, it is not logical to 

 generalize as to the mechanism of secretion of all electrolytes, 

 and our conclusions are confined therefore to the modus operandi 

 of iron elimination. 



What, then, is the nature of the factors altering in vivo the 

 distribution of the ferrocyanide? As it was suspected that it 

 might be a purely physical factor, the diffusion rates into solidi- 

 fied gelatin were determined as follows: Solutions of ferri-ammo- 

 nium citrate and sodium ferrocyanide were allowed to stand 

 above gelatin in test-tubes for forty hours, and then, the solu- 

 tions having been poured off, the gelatin was washed and treated 



THE AMERICAN JODRNAL OF ANATOMY, VOL. 29, NO. 1 



