EXCRETION 411 



flow would be diminished ; if both were relaxed, it would be 

 increased ; if only the vas afferens were affected, the changes 

 would be in the same sense, although less marked, since the 

 total alteration of resistance would be less. 



An experiment which is sometimes quoted as a decisive 

 test of the relative importance of changes in the rate of flow, 



FIG. 129. NERVES OF KIDNEY (BERKELY). 



(16) medium-sized artery with its nerve-plexus ; A, terminal knobs ; B, aberrant 

 branch ending in terminal knob E; the dotted lines outline the artery. (17) Nerve- 

 fibres surrounding a Bowman's capsule, which is indicated by a dotted line ; some of 

 the endings are close to the membrane ; (18) convoluted tubule shown in outline with 

 fine nerve-fibres on it, which seem to enter the basement membrane. 



and in the pressure of the blood within the glomeruli, is that 

 of tying the renal vein. This undoubtedly does not lower the 

 intra-glomerular pressure on the contrary, it must increase 

 it but the secretion of urine stops. If the venous outflow 

 from the kidney is only partially interfered with, the flow of 

 urine is immediately diminished, but the administration of 

 a diuretic like potassium nitrate causes an increase. It is 

 suggested that in these experiments the secretion stops or 

 slackens because an active circulation, and not a high 

 blood-pressure, is its necessary condition. The conclusion 

 is probably correct, but the experiment does not prove it. 

 For few glands can go on performing their function after the 

 circulation has ceased. The kidney must be able to feed 



