446 PHYSIOLOGY CHAP. 



blood is not adequate for the nutrition of the excised kidney. It 

 would be better, in experimenting on artih'cial circulation, to 

 employ perfectly normal blood prevented by appropriate treatment 



from coagulating. 



VI. The Renal Circulation is certainly under nervous control, 

 so far as regards regulation of pressure and rate of blood-flow in 

 the vessels of the kidney by active constriction or dilatation of 

 the renal artery and its branches. The vasomotor system of the 

 kidneys is no less developed than that of any other vascular region, 



FIG. 117. Roy's mimim-tiT (open and empty), for study of variations in volume nl tlic kidneys. 

 Metal box, of approximately the same shape as the kidney, which opens by a hin.ur. K.-n-h 

 half of the box contains two chambers, an outer A, and an inner It. The two upper chambers, 

 from the top of which the two-way tube K passes out, are clamped together by screw C. The 

 lower chambers are clamped by a similar screw. The box closes by the hook D, which 

 sui rounds the hollow tube L, through which the renal vessels and the ureter pass out from 

 the enclosed kidney. 



hence it is not difficult to recognise its effects by the eye. After 

 cutting the branches of the renal plexus that accompany the 

 artery as it penetrates by the hilum, paralytic dilatation of the 

 vessels of the external capsule can be seen. After excitation of 

 the renal plexus or spinal cord, the amount of blood flowing back 

 from the gland by the vein is diminished, and becomes blackish 

 with the character of venous blood, the secretion of urine being 

 arrested, while under normal conditions, when the kidney is 

 functioning, the blood remains, as we have seen, bright red like 

 arterial blood. Stimulation therefore produces constriction of 

 the renal vessels. 



The most elegant method of demonstrating vasomotor action 

 on the renal circulation is undoubtedly that of the plethysmograph, 



