60 E. J. STIEGLITZ 



specific gravity appearing when iron is present in the urine was 

 such a constant one that it cannot be without considerable signi- 

 ficance, particularly as it is correlated with the inhibitory or block 

 effect of iron on the passage of phenolsulphonephthalein, car- 

 bonates, probably calcium, and certainly of iron itself. 



Were there a diuresis during the iron excretion one might 

 assume the urine to be diluted because of the more rapid glo- 

 merular filtration of water, but no diuresis exists at this time. 

 In fact, the findings are to the contrary, as there is a diminished 

 elimination of water during iron excretion, as recorded and 

 discussed under series III. Therefore, the urine cannot be 

 diluted by the addition of an excess of water, and the only 

 remaining explanation is that the presence of iron obstructs the 

 secretion of an appreciable proportion of the urinary solids by 

 the mechanism discussed above. 



Therefore, we believe to have shown in this series of retention 

 experiments that the cells of the convoluted tubules do not 

 secrete all the iron that reaches them from the blood, but retain 

 an appreciable quantity. This retention is accumulative with 

 multiple injection of iron, and such an accumulation not only 

 interferes with the secretion of iron as evidenced by a prolonga- 

 tion of the period of elimination and a diminution in the quan- 

 tity excreted, but also inhibits the passage of other substances, 

 and is therefore associated with a fall in the specific gravity of 

 the urine. It is quite certain that this block or inhibition is 

 essentially correlated with, and probably due to, an altered state 

 of the cytoplasmic colloids brought about by the presence of the 

 trivalent active ferric ions. 



Series III 



A closer study of the changes in the urine and their relation to 

 the interval after injection during the period of iron elimination 

 promised to throw more light upon the mechanism of iron secre- 

 tion by the kidney, and further investigations by means of 

 catheterization experiments were carried out. The technique 

 of these experiments was as follows: a rabbit, tied to the table 



