70 E. J. STIEGLITZ 



In comparing this curve with the results for iron injections 

 without the addition of caffeine as a diuretic, one notes that the 

 most striking feature is the much more prompt appearance of 

 the iron in the urine and the greater brevity of the period of 

 ehmination, being 160 instead of 300 minutes. In all other 

 respects the curves are similar. Corresponding with the short- 

 ened time of iron excretion, the rise in urine volume appears 

 much earlier, but it is in the same relative position as before. 

 The caffeine, although a diuretic known to increase the flow of 

 urine, is unable to neutralize the inhibition of the iron, but as 

 soon as that is removed a delayed diuresis occurs, as evidenced 

 by the great volume of the last sample. It is not within the 

 scope of this paper to enter into a detailed discussion of the phar- 

 macodynamic action of caffeine and its related diuretics, but it 

 is apparent, from the increased speed of iron secretion, that in 

 some way it stimulated the cells of the convoluted tubules to 

 greater activity and that there was a true diuresis, therefore, 

 despite the decreased secretion of water. Iron is secreted more 

 rapidly, water inhibited bj^ the iron. That the caffeine can do 

 this indicates that the route of the two substances, solvent and 

 solute, is possibly not the same. 



Series IV 



The behavior of ferrocyanide in the body when introduced 

 intravenously is quite different from that of the trivalent ferric 

 ion. This was first demonstrated in this work by experiment 

 K29 and later checked by a similar experiment, K49, both of 

 the type of investigation described under series I. Prussian 

 blue, precipitated by means of ferric chloride, was found in a 

 diffuse form throughout the connective tissue, the renal pelvis 

 and sinus and lymphatic spaces in the kidney sections and never 

 in distinct granular form. Biberfield (77, 78) and Easier (79) 

 record finding the Berhn or Prussian blue in the interstitial 

 tissues only and support their statements with figures. They 

 are unable to draw any conclusions as to the pathway through 

 the kidney, but find, as our experiments also show, that it appears 



