MECHANISM OF RENAL SECRETION 41 



These later figures check even more closely, and therefore we 

 conclude that the green salt is composed of two ferric citrate 

 molecules combined with one of triammonium citrate, while the 

 other contains a diammonium citrate. In the brown diammo- 

 nium salt there is left one free carboxyl group which probably 

 is the point of difference determining the toxicity. This view is 

 further supported by the fact that on the addition of a slight 

 amount of ammonium hydroxide to the toxic green salt, the 

 toxicity is lost. Further, the green salt loses ammonia slowly, 

 as determined by an examination of the air above the salt in the 

 bottle containing it, and then shows toxic qualities. Therefore, 

 we believe the green salt to be unstable, tending to lose ammonia 

 and thus, through freeing a carboxyl group, becoming more 

 toxic, and that the brown salt is merely a stage of more com- 

 plete loss of the one molecule of ammonia. In experiments 

 K73, K75, K76, K77, K78, K79, K81, and K82 all the animals 

 died from the decomposed green salt. In all instances, as with 

 the brown salt, there were marked nervous symptoms, con- 

 vulsions, and respiratory distress. The convulsions appeared 

 suggestive of vestibular disturbance, but no apparent change 

 could be found in sections of the brain stem of K81, and the 

 other tissues also seemed normal. 



The fixation of the kidney tissues to be studied required a 

 dual reaction. First, the tissues themselves must be fixed in a 

 satisfactory manner and, secondly, the iron must be precipitated 

 in the cell in the exact position that it had at the time of death. 

 Any diffusion of the iron during the fixation would of course 

 obscure any attempts to localize the iron. Aqueous reagents, 

 such as plain Zenker's fluid, formol Zenker, formalin, and acetic 

 acid Zenker, were first used, but although these yielded good 

 results in tissue fixation, the iron was diffuse. Therefore 95 per 

 cent alcohol was tried as a fixative, and it was found to yield the 

 most satisfactory result, as diffusion of the salt was apparently 

 eliminated entirely. There was some shrinkage due to the rapid 

 dehydration, but control fixation with Zenker's fluid was always 

 used to check the normal condition of the tissue. 



Hall (46), in a series of experiments on the fixation of inorganic 

 iron in tissues, found that pure alcohol fixes the iron in the same 



