1280 PHYSIOLOGY 



the urinary secretion, which could be reinduced by injection of 

 urea. He concluded that urea with water was secreted by the 

 tubules, whereas peptone, sugar, and haemoglobin were turned out 

 by the glomeruli. Beddard showed that these results of Nussbaum's 

 must have been due to the fact that he had not obstructed the 

 whole of the renal arteries. One or two of these small vessels will 

 suffice to supply blood to a considerable number of the glomeruli. 

 After complete obstruction of the arteries, no urinary flow could 

 be induced even with subcutaneous injection of urea. But the 

 cutting off of the arterial blood-supply from the tubules caused a 

 rapid destruction of the tubular epithelium, so that the result of the 



-Aorta 



-Vena cava 



Test-is 



"Renal arteries 



I I -^^BW^JI7> / 



Kidney 

 Renal porhal- 



Anf. abdom.v- 



- Femoral v. 

 FIG. 533. The vascular supply to the kidney in the frog. 



experiment could not be taken as negativing the possibility of this 

 epithelium having, when in a normal state of nutrition, some secretory 

 power. He therefore carried out, with Bainbridge, another series of 

 experiments of the same description, in which the frogs, after ligature 

 of the renal arteries, were kept in an atmosphere of pure oxygen. 

 Under these circumstances sufficient oxygen diffused into the blood 

 of the renal portal vein to maintain an adequate supply of this gas to 

 the tubules. No desquamation of the epithelium resulted, and in- 

 jection of urea produced a small flow of urine even when, by subsequent 

 injection of the blood-vessels, it was proved that every glomerulus had 

 been cut out of the circulation. Similar results have been obtained 

 by Brodie and Cullis in certain experiments in which oxygenated 

 Ringer's fluid was led by the renal portal vein through the surviving 

 kidney of the frog. A small flow of urine was obtained, especially 

 after urea or potassium nitrate had been added to the fluid. The 

 quantities of urine obtained in these experiments were too small to 

 admit of a proper analysis or of a comparison of their molecular 

 concentration with that of the blood-serum of the animal. 



