68 E. J. STIEGLITZ 



we have seen that the blood-vessel lumina give a positive Prus- 

 sian-blue reaction up to a point of twelve minutes after the 

 injection. Harvey and Bensley (76) record somewhat similar 

 findings in their work on the gastric secretion of hydrochloric 

 acid. Therefore, the duration of the free circulation of uncom- 

 bined iron is probably quite brief, although it is quite possible 

 that it circulates in a masked form, combined with serum col- 

 loids (proteins) with either chemical or physical bonds. Such 

 iron would probably be inactive, as it is already bound to protein. 



With the disappearance of the free and active iron from the 

 circulation, the tendency for the body colloids to liberate water 

 stops. Therefore, there is consequently no more stimulation to 

 diuresis. Furthermore, the increasing accumulation of iron intra- 

 cellularly in the walls of the convoluted tubules of the kidney 

 begins to take effect. As we have just stated, we see that either 

 the ferric or citrate ions alone, or more so together, reduce the 

 tendency of colloids to adsorb water, and therefore the presence 

 of either substance, but especially the ferric ion, in the cytoplasm 

 of any secretory cell would tend to inhibit the passage into that 

 cell of water or other substances, for the solutes cannot well 

 enter if their solvent, water, is repelled. 



Such is the mechanism we believe to be responsible for the 

 initial, very transient diuresis and the later obvious inhibitory 

 action of the iron to water secretion, and also to the solids of the 

 urine, as evidenced by the decreased specific gravity during iron 

 elimination. The apparent contradiction of Fischer's conclu- 

 sions and results is due to two factors: 1) The fact that his 

 injections of diuretic salines were slow and long continued, the 

 body plasma therefore having a continuous supply of the saline, 

 while in our experiments the administration of iron was by a 

 single, rapid injection of the ferric salt, and, 2) that iron is con- 

 spicuously a salt w^hich rapidly and thoroughly becomes localized 

 intracellularly — a characteristic not described for the cations 

 which Fischer worked with. 



In one experiment (K67) similar to those showing the secretion 

 curves of iron and water, 1 grain of caffeine sodiobenzoate was 

 injected in the same solution with the ferric ammonium citrate 

 and the following results obtained (table 4 and chart 4). 



