MECHANISM OF RENAL SECRETION 55 



Recognizing that it was quite possible that either the proximal 

 or distal convoluted tubules alone retained (and therefore 

 secreted) the iron, and being unable to differentiate them accu- 

 rately in the alcohol-fixed preparations, two attempts (K72 and 

 K89) were made to apply Huber's technique of tubule isolation 

 to the iron-loaded ducts (53, 54). The animal of experiment 

 K72 had received five injections. The Huber method of injec- 

 tion of concentrated hydrochloric acid into the renal artery was 

 slightly altered by the addition of some sodium ferrocyanide to 

 the acid to make possible the immediate precipitation of the 

 Prussian blue. The kidneys became very dark blue, especially 

 in the cortex. All the proximal convoluted tubules that could 

 be identified with certainty contained iron, but not necessarily 

 uniformly, for some cells were deep blue, while their immediate 

 neighbors in the same tubule apparently contained no inorganic 

 iron. In a similar preparation from K89, the animal of which 

 had received four injections, the Huber micro-dissection showed 

 many convoluted tubules containing no blue and small areas of 

 blue in both the proximal and in some distal convoluted tubules. 

 In K72 the findings in the distal tubules were not certain, as 

 they were chiefly negative for iron. The glomeruli in both 

 experiments were all uniformly devoid of blue. In other words, 

 these experiments gave corroborative results which show that 

 the iron is carried by individual cells in probably either the 

 proximal or distal convoluted tubules (certainly in the former), 

 but that these cells must be specialized and differentiated in 

 some manner from their neighbors which do not retain and 

 probably therefore do not secrete iron. In search of further 

 evidence some kidney tissue containing iron (K96) was fixed 

 in Bensley's A. 0. B. reagent (50) for mitochondria and stained 

 by Altmann's technique, but the iron was in a diffuse form, demon- 

 strating the A. 0. B. reagent as unsuitable for the fixation of 

 iron. We believe that this subject of apparently highly local- 

 ized special function warrants further investigation and that it 

 is to be closely correlated with the studies of specific renal 

 pathology of Aschoff (28) and Suzuki (29) (series V) . 



