MECHANISM OF RENAL SECRETION 57 



cent and 21 per cent for the two hours, showing a striking decrease 

 in the excretion. Not only does the accumulation of iron inter- 

 fere with the further elimination of iron, but it greatly reduces 

 the ability to pass the phenolsulphonephthalein, known to be 

 secreted by the convoluted tubules. 



The normal urine of rabbits is usually rich in carbonates; so 

 rich, in fact, that it is generally turbid. This turbidity is lost 

 and carbon dioxide generated by the addition of acid to the urine, 

 which is alkaline to litmus. The carbonates are chiefly in the 

 form of the calcium salt, for otherwise the turbidity would not 

 exist. It was noted from the outset of the work that following 

 an injection of iron the urine became clear for several samples. 

 It also became brown (often quite dark) and gradually returned 

 to its normal pale and cloudy condition as the concentration of 

 iron diminished. The brown color was undoubtedly due to the 

 presence of ferric hydroxide (Fe(0H)3), as the urine was alka- 

 line and the color was lost on the addition of acid. It is diffi- 

 cult, however, to explain the disappearance of the carbonate 

 (iron containing urine did not give carbon dioxide with acid) 

 during iron excretion. Whether calcium elimination is also 

 inhibited at this time we cannot be certain, for it may have been 

 present in other forms and no specific tests for calcium were 

 made. According to Roehl (64), calcium is detected in the 

 outer two thirds of the cells of the convoluted tubules following 

 an intravenous injection of lime salts, and he concludes that 

 these granules are in close relation to the excretion of the salt. 

 This is a conclusion further supported by the accumulation of 

 lime and the formation of soaps (Klotz (65)) when the kidney 

 is damaged experimentally. Therefore it is quite possible that 

 if calcium follows the same route as iron in its excretion, the 

 presence of iron might interfere with and inhibit the passage of 

 calcium, as it certainly does with the carbonate ions. 



A further factor to be considered here, and also in connection 

 with the other inhibitions resulting from the presence of iron, is 

 its possible effect upon the physical condition of the cytoplasmic 

 colloids as a trivalent cation. Loeb (66) has shown that bivalent 

 cations, such as Mg, Ca, Sr, and Ba, do not cause excessive 



