50 . E. J. STIEGLITZ 



95 per cent alcohol. 

 Zenker's solution. 



Histological findings: Prussian blue was present in the cells of the 

 convoluted tubules, and appeared in all parts of the cells in different 

 instances. In many tubules the brush border was deep blue and the 

 intercellular membranes demarcated. There was some iron in the 

 blood-vessels (glomerular tufts) , but none in any of the capsular spaces. 

 There was only an occasional trace of blue in the lumina of the collect- 

 ing tubules of the medulla. 



Ten minutes {K50). Female guinea-pig. Weight = 720 grams. 

 Procedure and dose identical with those of the preceding experiment, 

 except that the animal was allowed to Uve ten minutes. 



Histologic findings: In the medullary portion iron was present in 

 the lumina of the collecting tubules. In the cortex the glomeruli and 

 their capsular spaces were negative. In the lumen and also in the free 

 border of the cells in occasional convoluted tubules granular iron was 

 found. Those tubules containing the iron were grouped (K37), while 

 many of the convoluted tubules showed no iron at all. 



Twenty minutes {K51). Female guinea-pig. Weight = 655 grams. 

 Procedures identical with those above. Dose = 0.13 gram (0.2 gram 

 per kilo body weight, as was used as a standard), and the animal killed 

 after twenty minutes. 



Histologic findings: The medullary collecting tubules contained 

 iron in their lumina. There was also some in the lumen and along the 

 brush border of some of the convoluted tubules. The glomeruK and 

 capsular spaces were negative. All in all, there was Httle iron in the 

 tissue, less than with a rabbit. 



Thus we have again, in a different species, results similar to 

 those seen in the rabbit and differing only in the quantity of 

 iron appearing, as the dosage is the same per kilo weight. There 

 is no deviation from the trend of progress as more completely 

 illustrated in the rabbit investigations. 



Such a series of consecutive pictures, illustrating the trend of 

 the iron to be from the periphery of the cells of the convoluted 

 tubules toward their border approximating the lumen, and the 

 presence of iron in the brush border only in the later periods of 

 time, indicates very strongly that the passage of iron from the 

 blood into the urine is by a mechanism of secretion through these 

 cells, rather than as a filtrate from the glomerulus. In no 

 instance was there a deviation from the general trend of the 

 movement as witnessed by the localization of the Prussian blue. 

 The negative evidence in regard to the finding of iron in the 



