MECHANISM OF RENAL SECRETION 51 



glomerular capsule and the capsular space is of little value alone, 

 because, as v. Sobieranski (10) and Brodie (14) have pointed out, 

 the flow of fluid from the malphighian body may be very rapid 

 indeed. Furthermore, negative evidence alone never carries 

 conclusive weight. But, this fact, coupled with the evident 

 localization of the intracellular iron, seems to warrant the con- 

 clusion that iron enters the urine through the secretion of the 

 cells of the convoluted tubules. Glaevecke (43) records similar 

 findings and arrives at the same conclusion. 



Series II 



The last example of the above series in the rabbit showed that 

 iron remained in the kidney for some time after the urine had 

 become negative. This fact led to the work upon another series 

 of experiments on the nature, both anatomic and physiologic, of 

 this renal retention of iron. Aschoff (28) believes it important 

 to differentiate the period of secretory activity and the 'Spei- 

 cherungs phase.' The phase of secretion (for the dyes Aschoff 

 used) reaches its height in an hour and then slowly falls, while 

 the phase of storage only reaches its height after twelve to 

 twenty-four hours. He concludes that storage or, as we have 

 termed it, retention is an independent process from secretion. 

 The results of our work, reported below, do not support such a 

 contention. 



The first fact sought for was the duration and behavior of the 

 retention following a single injection of iron. In experiments 

 K12 and K13, recorded above, we have seen that the cells of the 

 convoluted tubules, especially along their brush border, contain 

 the iron as long as 9.5 hours after the urine is negative with the 

 very delicate Prussian-blue test. How long this iron would 

 remain in the kidney following a single administration has not 

 yet been exactly determined, but one experiment (K37) was 

 carried out for the sake of an estimate, the animal being killed 

 eighty- three hours after an injection of the usual dose of the 

 green salt. It was about seventy-five hours after the urine had 

 become free of iron. The sections displayed a little iron present 



