MECHANISM OF RENAL SECRETION 49 



The urine aspirated from the bladder was negative for the iron test. 



Histological findings: The medullary portion of this kidney was 

 entirely negative for iron, as one would expect, as the urine of the 

 animal had been negative before death occurred. But there was an 

 appreciable amount of iron in the section. This was confined entirely 

 to the cytoplasm of the cells of the convoluted tubules, at their border 

 toward the lumen. Here again, there appeared to be iron right in 

 the brush border of the cells in some cases, and it was noted that in 

 some tubules the cells were heavily laden, while in others the cells did 

 not contain any iron at all. This important point will be more fully 

 discussed later in the paper. 



Five hundred and sixty minutes {K12). Large albino male rabbit. 

 Injected 0.8 gram filtered brown ferric ammonium citrate solution intra- 

 venously. Animal showed toxic symptoms. Died in nine hours and 

 twenty minutes. Autopsied at once. Ividneys fixed in: 

 95 per cent alcohol. 

 Zenker's fluid. 



The urine in the bladder was negative for iron. 



Histological findings: In the histologic preparations of this experi- 

 ment the localization of the iron was exactly the same as noted in the 

 previous experiment (K13). It was further noted that in both this 

 period and the shorter interval of 330 minutes, those tubules which 

 contained the iron in large amounts were distinctly grouped together 

 and localized. The reasons for this will be discussed later. 



The above-described type of experiment was repeated in 

 shorter sets in three mammalian species other than the rabbit, 

 namely, with the guinea-pig, cat, and dog. Essentially the 

 same technique was employed except that a light ether anes- 

 thesia aided in making the intravenous injection. With each 

 species three experiments, of typical time intervals of three, ten, 

 and twenty minutes, were carried out. In the series with the 

 cat the section fixed in Zenker's fluid and stained with hema- 

 toxylin and eosin in routine to check the normality of the tissue, 

 showed all the animals to have been nephritic and therefore the 

 results must be completely discarded. The same was unfor- 

 tunately true of two of the dog experiments. The guinea-pig 

 series, however, was normal throughout, as were all the rabbits 

 used in the observations recorded above. 



Three minutes {KJ^O). Female guinea-pig. Weight = 740 grams. 

 Injected 0.15 gram green ferric ammonium citrate into the femoral 

 vein, exposed under light ether anesthesia. Animal killed by bleeding 

 three minutes later. Kidneys fixed in: 



