49& EXCRETION 



arteries going to the kidney are tied the glomeruli are completely 

 and permanently deprived of blood. The spontaneous secretion 

 of urine is totally stopped, as Nussbaum found, but only in three 

 experiments out of eighteen was it possible to start the secretion 

 by injection of urea. The epithelium of the tubules degenerated 

 and desquamated after complete ligation of all the renal arteries, 

 showing that it requires some arterial blood as well as the venous 

 blood from the renal portal to maintain its vitality. The degenera- 

 tion of the epithelium can be prevented by keeping the frogs in an 

 atmosphere of oxygen after ligation of the arteries. In six such 

 frogs, in which the complete elimination of the glomeruli was con- 

 trolled by subsequent injection, secretion of urine followed the 

 injection of urea, alone or in combination with dextrose, phlorhi/dn, 

 or di-sodium hydrogen phosphate (Na 2 HPO 4 ) . In all the cases the 

 urine contained urea, chlorides, and sulphates, and was acid to 

 phenolphthalein. In one case after injection of urea and dextrose, 

 and in another after urea and phlorhizin, the urine reduced Fehling's 

 solution, and therefore presumably contained dextrose (Beddard 

 and Bainbridge). When the frog's kidney is perfused in situ with 

 oxygenated salt solution a certain flow of urine takes place. Sub- 

 stitution of non-oxygenated saline markedly slows the flow (Cullis). 



Apparently, then, the tubules have the capacity to secrete prac- 

 tically all the constituents of urme, and when the flow of urine is 

 small, probably most of it comes from the tubules. When, as in 

 the diuresis produced by salt solutions, large quantities of water 

 and salts have to be rapidly excreted, the bulk of the liquid comes 

 from the glomeruli, but also by a process of secretion. 



Lindemann has endeavoured to exclude the glomeruli in mam- 

 mals by injecting oil through the renal artery. After a short time, 

 according to him, the oil emboli clear away from practically all 

 parts of the kidney except the glomeruli, which remain plugged. 

 If indigo-carmine be subsequently injected into the blood, it is not 

 only taken up from it by the embolized kidney as well as by a normal 

 one, but is excreted. The quantity of urine is much diminished, 

 and its specific gravity increased, but its composition is not essen- 

 tially altered. He infers that the tubules are in a high degree 

 independent of the glomeruli as an apparatus for the secretion of 

 urine. More conclusive observations have lately been reported in 

 which the tubules were eliminated by producing an artificial nephritis 

 in rabbits by the subcutaneous injection of sodium tartrate. Tar- 

 trates act mainly upon the tubules, causing no, or a much smaller, 

 effect upon the glomeruli. After the intravenous infusion of a 

 solution containing sodium chloride and urea during pronounced 

 tartrate nephritis, all the chlorine appears in the urine within forty- 

 eight hours, but little, if any, of the urea. In the light of the 

 histological findings, this is interpreted to mean that under normal 

 conditions chlorides and water are passed through the glomerular 



