38 E. J. STIEGLITZ 



METHODS 



Iron, for the purpose of tracing its course in the kidney, from 

 the blood to the urine, has many advantages. In the first place, 

 it forms ionized salts whose presence may be detected by very 

 delicate but intense color-precipitation reactions leading to the 

 formation of Prussian blue. This precipitation test is so delicate 

 and so specific for iron that it may be used as a microchemical 

 test in the finest histologic work. Furthermore, ferric salts, 

 being electrolytes, should resemble in their excretion the behavior 

 of other salts found in the urine. Iron is normally to be found 

 in urine, and it increases greatly in those diseases involving the 

 hematogenic apparatus. The normal presence of iron was first 

 pointed out by Tiedemann and Gmelin in 1820 and afterward 

 confirmed by a host of observers, although Becquerel, Herberger, 

 Lehman, and Schlemmer denied its normal elimination via the 

 urine because their methods were inadequate to detect the mi- 

 nute amounts. The accepted normal estimation for iron equals 

 1 mgm. per twenty-four hours for a human being (Neumann 

 (38), Neumann and Mayer (39) and Kennerkneckt (40)). 



A further advantage in the use of salts of this element is 

 that normal kidney does not contain any free (ionized) iron to 

 cause a recognizable color reaction. This was determined by 

 control experiments. Macallum (41) makes especial note of the 

 absence of iron in renal cells. Therefore, any iron seen in the 

 sections in the form of Prussian blue comes from the iron that 

 has been administered to the animal. It was suggested that 

 phosphates be used in place of the ferric compounds, but the 

 objection that there were already phosphates present, which 

 would interfere with the tests, ruled them out (42). 



The use of iron in investigations of the mechanism of renal 

 activity is not new. Glaevecke (43) as early as 1883 employed 

 ferric citrate for such work. This salt was administered by sub- 

 cutaneous injection. The first appearance of the iron in the 

 urine, following such an injection, was one-half hour later. The 

 iron concentration remained at its height from two to four 

 hours following the injection, while the urine became negative 

 only after a period of twenty-five hours. He also reports nega- 



