394 



ESSENTIALS OF PHYSIOLOGY. 



R.PV 



of blood through the glomeruli is completely cut off, but the tubules are 

 still supplied with venous blood from the renal portal vein. The cutting 

 off of the supply of arterial blood to the kidneys is followed by destruc- 

 tion of the epithelium of the 

 tubules, and the frogs secrete 

 no urine. If, however, the frogs 

 are kept in an atmosphere of 

 oxygen after ligature of the 

 renal artery, sufficient oxygen 

 is absorbed and carried to the 

 tubules to replace that normally 

 supplied to them by the arterial 

 blood leaving the glomeruli ; 

 and the nutrition of the tubules 

 is maintained. In these cir- 

 cumstances the frogs form small 

 quantities of urine, and, since 

 the glomeruli are excluded, this 

 must come entirely from the 

 renal tubules ; it is acid in re- 

 action, and contains urea and 

 salts. 



In mammals the injection of 

 substances such as sodium sul- 

 phate or urea into the blood leads to an increased flow of urine, which 

 then contains a higher percentage of sodium sulphate or urea than is 

 present in the blood ; and at the same time the consumption of oxygen 

 by the kidney is greatly increased. 



FV. 



FIG. 132. The blood supply to the kidney 

 of the frog. 



A., aorta; R.V., renal vein; R.P.V., renal-portal 

 vein; F.V., femoral vein; A.A.V., anterior 

 abdominal vein. 



Since these changes may occur with little or no alteration in the 

 volume of, or the rate of blood flow through, the kidney, the additional 

 urine formed in these experiments must have been secreted by the 

 tubules. This conclusion is confirmed by the fact that when the renal 

 tubules are poisoned with drugs, such as corrosive sublimate, the 



