THE SECRETION OF URINE 



1141 



active dilatation of the renal vessels, and a consequent rise of pressure and 

 velocity of the blood in the glomeruli. That the vascular change is really 

 responsible for the increased urinary flow is shown by the fact, determined by 

 Cushny, that if the swelling of the kidney be prevented by means of an 



100 110 1'20 ISO UO 150 



FIG. 533. A comparison of the effects of intravenous injection of 30 grm. glucose 

 in concentrated solution on the arterial blood -pressure, the concentration of the 

 blood, the kidney volume, and the urinary flow. Abscissa = time in minutes. 



adjustable clamp on the renal artery, no diuresis is produced ; so long as 

 the kidney is kept at its normal size the flow of urine remains at the same 

 rate as before. 



With regard to the specific diuretics, such as caffeine, the question is 

 not quite so clear. In most cases injection of caffeine in the rabbit brings 

 about a dilatation of the kidney and a proportional increase in the secretion 

 of urine. But cases have been recorded in which expansion of the kidney 

 occurred without any increase in urinary flow, and, on- the other hand, 

 augmented urinary flow without any increase in the kidney- volume, or 

 even in the rate of blood-flow through the kidney (as determined by Brodie's 

 method). The general rule, however, is that a greater rate of blood- flow is 



