MECHANISM OF RENAL SECRETION 45 



the latter alone) in a diffuse form and in the connective tissues 

 all over the body. This marked difference in behavior will be 

 discussed under series V. 



A most striking characteristic of the sections of series I was 

 the entire absence of iron in the lumina of Bowman's capsules. 

 In over three hundred fifty Prussian-blue preparations studied, 

 iron was found in no case in the spaces of Bowman's capsules, 

 although iron was often present in quite marked amounts in the 

 capillaries of the glomerular tufts, and separated from the lumen 

 only by the endothelium and the glomerular epithelium (43). 

 On the other hand, iron was found in considerable amounts in 

 the cells and lumina of the convoluted tubules. 



In brief outline form, the histologic findings of iron in the 

 above series is as follows: 



One-half minute (K83). Female rabbit. Weight = 1550 grams. 

 Injected 0.3 gram ferric citrate intravenously. The animal died imme- 

 diately at the end of the injection, without a struggle, apparently as a 

 result of embolism. Kidneys were fixed in: 



95 per cent alcohol. 



Zenker's solution. 

 Histologic findings: There was much iron in the blood-vessels and 

 glomerular tufts, but none in any of the capsular spaces or in the con- 

 voluted or collecting tubules. With the Zenker control sections semi- 

 scattered areas of round-cell infiltration and slight dilation of some of 

 the medullary tubules were observed. 



Two minutes {KS5). Young male rabbit. Weight = 1450 grams. 

 Injected 0.3 gram green ferric ammonium citrate plus 0.3 gram sodium 

 ferrocyanide intravenously. Animal killed two minutes after the 

 injection. Kidneys fixed in: 



5 per cent trichloracetic acid. 



Carney's fluid with trichloracetic acid. 



Zenker's fluid with trichloracetic acid. 



Zenker's fluid. 



95 per cent alcohol. 

 The bladder urine was negative for iron at death. 

 Histologic findings: In this experiment the major part of the iron 

 was found in the blood-vessels, especially noticeable in the glomerular 

 tufts of the malpighian bodies. There was no iron in the lumen of 

 Bowman's capsule. There was some iron in the cytoplasm of the cells 

 of the convoluted tubules, distributed in both borders of the cells and 

 in every position in the cytoplasm in different cells. In the greater 

 number of cases, however, the iron was in the portion of the cells away 

 from the lumen. There was also some iron present in the thick limbs 



