MECHANISM OF EENAL SECRETION 67 



of the body they Uberate water from them and their diuretic 

 activity is but an expression of the amount of water they are 

 thus able to hberate." Iron (18, p. 51) being the most active 

 cation and the citrate radical the most powerful anion in dehy- 

 drating colloids, ferric ammonium citrate should be an efficient 

 diuretic. How, then, can one conceive of the above results, 

 shovring considerable inhibition to water elimination, being 

 compatible with Fischer's theory? They are, however, quite 

 compatible therewith, as is clear from the f ollovring considerations. 



In all three of the catheterization experiments there is a 

 slight and very transient rise in the rate of flow at the very 

 outset of the iron elimination. This may be due to any one of 

 several factors; one of the simplest being the nervous and vaso- 

 motor stimulation occasioned by the fright and excitement of 

 the animal during the injection. Such an explanation would 

 not hold for the later, greater and permanent rise occurring with 

 the decreasing concentration of iron, for at that time the animal 

 is not disturbed. The brief rise might also be due to the increased 

 blood volume due to the addition of the injection fluid to the 

 circulation (dose usually dissolved in 10 cc. distilled water), but 

 that is unlikely; or, lastly, to the fact that at that time, imme- 

 diately after the intravenous injection of iron, the system is 

 freely reacted upon by the ferric ion, the colloids altered so that 

 they tend to lose water and then this excess of water must be 

 eliminated by the kidneys. 



Series I having shown how quickly the iron became localized 

 intracellularly, the question arose as to how long the iron remxained 

 in the blood stream. Several experiments are included in this 

 group, (K33, K38, K39, K40, K43), but in none was a conclusive 

 result obtained, partly because the hemoglobin of the blood 

 obscured the test by forming brown methemaglobin with the 

 acid in the reaction. If iron Vv^ere present it would be in very 

 dilute solution and therefore a trace of blue would be lost in the 

 deep brown. Furthermore, it is possible that the iron, when in 

 the blood stream, is in combination with one or more of the 

 serum proteins, and therefore insensitive to the test employed 

 (49). From a study of the histologic preparations in series I 



