222 VRINE 



fact appears to be that at present we have no histological 

 method of distinguishing between two opposite processes. 



2. Nussbaum's Experiment.— Nnsshaum sought hght on 

 the subject from the frog's kidney. In the amphibian, it 

 will be remembered, the renal artery supphes first the 

 glomerulus, then the tubule, as in the mammal, but the 

 tubule receives, in addition, blood conveyed from the hmbs 

 by the renal portal vein. Ligature of the renal artery 

 causes stoppage of secretion; the tubules alone, therefore, 

 are unable to secrete urine. But when urea is injected into 

 the renal portal vein some secretion occurs. Sodium 

 sulphindigotate on injection is deposited in the lumen of 

 the tubules. The vahdity of the appUcation of these results 

 to the mammahan kidney may be questioned, for although 

 structurally similar, amphibian and mammahan kidney are 

 developmentally different. As to the results themselves, 

 they are discordant with results obtained from perfusion 

 of the frog's kidney. 



3. Attempts have been made to decide the question by 

 noting the effect of partial obstruction of the ureter on the 

 composition of the urine. This operation causes a well- 

 marked reduction in water and chloride and a shght 

 reduction in urea and sulphate. For the followers of 

 Heidenhain this means decreased secretion at the glomer- 

 uh. For the followers of Ludwig it means increased 

 absorption. 



Experiments in which the tubules have been removed by 

 gouging out the medulla may be dismissed as causing too 

 much injury to the kidneys. Similarly attempts to poison 

 the tubules by injection of mercuric chloride are open to 

 the objection that the permeabihty of the glomeruh is 

 altered by this procedure. 



It is clear that the formation of urine can only be 

 accounted for by filtration when its composition is that of 

 plasma minus proteins. This is the case in the diuresis 

 caused by injection of Ringer's solution. When the com- 

 position of the urine difEers from this the process must be 



