MECHANISM OF RENAL SECRETION 53 



number of injections, were similar. In all cases considerably 

 more iron was observed than following a single injection. 



Having noted the evident accumulative nature of the iron 

 retention in the secretory cells, it was believed that frequent 

 long-continued, multiple injections might lead to a condition of, 

 block in the passage through the cell. Considering the iron to 

 be passing by absorption from the urine to the blood, such a 

 block should make the elimination of iron in the urine more 

 complete and more rapid. But, on the other hand, if the block, 

 either complete or partial, obstructs the passage of the iron 

 through the cells from the blood to the urine, the elimination of 

 iron should be both decreased and delayed. This question was 

 investigated in a series of experiments on rabbits in which the 

 animals were kept in metabolism cages and each sample of urine 

 studied during a course of injections, and we were able to obtain 

 a point where the block to iron elimination was very marked. 



The first indication of an obstruction to the passage of iron 

 was in the prolongation of the period of elimination. Following 

 an intravenous injection of the iron salt, the normal period dur- 

 ing which the urine remains positive is from four to six hours, 

 but varies somewhat with each animal. In K30 (see above) 

 the first period of iron elimination was approximately fifteen 

 hours (the animal was not normal), the period following a second 

 injection was forty-eight, and the third period forty hours. In 

 K36, in which a normal male rabbit weighing 2350 grams was 

 given nine intravenous injections over a period of twenty-eight 

 days, the record of the tests for iron in the urine, taken every 

 time a sample was voided, showed a constantly increasing 

 period of elimination, until, following the last injection, it took 

 68.5 hours for the urine to become free of iron. This result 

 might well be due to a block or impairment of activity on the 

 part of the glomeruli; but if this were the case, the urine volume 

 should show a progressive fall from day to daj'' as the block 

 increased. But such was not true, as the volume curve showed 

 a very irregular secretion of urine, but without any progressive 

 fall or rise in the amount. The suspected absence of any glomer- 

 ular injury and the presence of an injury of, or an accumulation 



