MECHANISM OF RENAL SECRETION 83 



SUMMARY 



In summary of the results directly concerned with renal secre- 

 tion recorded above, the following facts have been established: 



1. There is a definite movement of iron from the periphery of 

 the cells of the convoluted tubules to the lumina of the tubules, 

 as evidenced by the Prussian-blue reaction. 



a. No iron was at any time seen within the lumina of Bow- 

 man's capsules, even when it was present in the blood of the 

 glomerular tuft. 



h. The iron remains longest in the cells at their free periphery, 

 just under, or in, the brush border during the period of iron 

 elimination. 



c. The ferric iron appears in a particulate form intracellularly; 

 it is never found diffusely in the interstitial connective tissues. 



d. Similar findings were observed in guinea-pigs as in rabbits. 



2. Iron is retained in the cells of the convoluted tubules of 

 the kidney after the actual secretion has ceased. 



a. This retained iron remains present for at least eighty-three 

 hours following a single injection, and probably remains longer, 

 especially under the brush border. 



h. The retained iron is confined to certain tubules and pri- 

 marily to the proximal portion of the convoluted tubules; some 

 cells contain much, while their immediate neighbors are free 

 thereof. 



c. The retention is accumulative with multiple injections. 



d. The intracellular accumulation of iron produces an increas- 

 ing block to its secretion into the urine; this block is evidenced 

 by prolongation of the period of elimination and by diminution 

 of the amount excreted. 



e. The secretion of phenolsulphonephthalein is similarly inter- 

 fered with by the iron retention in the convoluted tubule cells, 

 and apparently also the elimination of calcium carbonate. 



/. The intracellular presence of iron inhibits the excretion of 

 water, evidenced in this series by the decreased volume during 

 iron elimination and the appearance of ascites in retention 

 animals. 



