MECHANISM OF RENAL SECRETION 61 



in the dorsal position, is catheterized and the bladder emptied; 

 the usual dose (0.2 gram per kilo weight) of iron salt injected 

 into the marginal ear vein and specimens of urine continuously 

 collected, measured, and tested for iron at frequent intervals. 

 The same quantity of urine and reagent were used in each test 

 reaction, so that the colorimetric results could be read as trace, 

 one, two, or three plus. The resultant data were charted. 



The first of these experiments (K9) failed because the toxic 

 brown ferric ammonium citrate was used and the animal died. 

 In experiment K43 the following curve was obtained (chart 1) : 



This experiment was twice repeated (K46 and K60) with very 

 similar results (chart 2). 



All three of these curves agree so uniformly that the results 

 may be considered as not due to chance or individual variation. 

 The plateau of the iron secretion curve in reality probably should 

 be a uniform rise and fall, but the triple plus readings were of 

 such a dark blue that it was impossible to make higher readings. 

 All the measurements of volume have been corrected, inasmuch 

 as the intervals between taking samples are not uniform. The 

 volume in cubic centimeters was divided by the number of 

 minutes since taking the previous specimen and that figure 

 multiplied by ten, putting all the reading upon an equivalent 

 basis. 



One of the striking characteristics of the iron-excretion curve 

 is that the salt does not appear earlier than ten minutes after the 

 end of the intravenous injection. In several other experiments 

 of the type recorded under series I and II where the animals 

 were kept in metabolism cages, and also in K9, this fact was also 

 conspicuous when the animals incidentally urinated immediately 

 or soon after the injection. In no such instance could a positive 

 test for iron be obtained before ten minutes. A part of this 

 latent period may be due to the time necessary for the urine to 

 reach the bladder, for the delivery of the iron to the kidney is 

 virtually immediate in an intravenous injection. This latent 

 period alone contraindicates any passage of iron through the 

 glomeruli, for other substances may appear in the urine in less 

 than a minute. However, such evidence is only of value in the 



