MECHANISM OF RENAL SECRETION 43 



although Carney's fluid with crystaUine (anhydrous) acid, in 

 place of the glacial acetic acid usually added, proved very satis- 

 factory. The substitution of trichloracetic acid in Bensley's 

 A. O. B.2 fixative proved a failure, as the efficiency in the preser- 

 vation of the mitochondria was destroyed (47). In making the 

 injections of the mixture of sodium ferrocyanide and the green 

 ferric ammonium citrate, chemical equivalent amounts were 

 used, with a dosage of the ferric salt equal to 0.2 gram per kilo 

 body weight. By calculation it was determined that the ratio 

 of equivalent weights was as 1 is to 1.06, and therefore in the 

 work equal weights of the two salts were utilized. 



Rabbits were the animals chiefly used, although some work 

 was done with dogs, cats, and guinea-pigs. In all instances the 

 salt w^as administered intravenously to insure more accurate 

 time relations and eliminate the uncertainty of the time required 

 for absorption. This forms a distinct improvement over the 

 method of Gaevecke (40). A few experiments were also done 

 with sodium ferrocyanide. 



The investigations reported on in this paper may now be class- 

 ified under several headings or series. The first of these (series 

 I) was the original nucleus of the work and consisted in a series 

 of preparations of the kidney from animals which had received 

 intravenous injections of iron salts and had been killed at vary- 

 ing periods of .time after the end of the injection. By such a series 

 it was expected that one could note the direction of movement 

 of the iron through the cells of the convoluted tubules, as the 

 consecutive photographs of the cinema reveal motion. This 

 series was carried out in full with the rabbit and shorter sets of 

 experiments performed with tiie dog, cat, and guinea-pig. 



Series II consists of a group of experiments pertaining to the 

 retention of the iron by the organism and especially by the cells 

 of the kidney and the physiologic eft^ects of such retention. 

 Series III includes a set of observations dealing further with iron 



^ Bensley's A. O. B. fluid consists of: 



2 per cent osmic acid 6 cc. 



2.5 per cent potassium dichromate 24 cc. 



Glacial acetic acid 1 drop 



