ACTION OM THE KIDNEYS. 471 



accordingly proceeded to try whether it had or not. The 

 manner in ^hich we experimented was as follows. A dog was 

 ana3sthetised with chloroform, the anaesthesia being kept up 

 during the whole operation. A cannula was placed in one 

 ureter so that tlie urine dropped from the kidney as fast as it 

 was secreted, and the rapidity of secretion could be readily 

 ascertained. The carotid artery was connected with a kymo- 

 graphion and the blood-pressure measured. On then injecting 

 a dose of casca into the jugular vein, we found that the blood- 

 pressure rose and the urine began to be secreted more rapidly. 

 An additional dose raised the blood-pressure still higher, but 

 the secretion of mine began to get slower instead of quicker, 

 and when the blood-pressure had risen to its maximum the 

 secretion stopped altogether. After a while the blood-pressure 

 began to fall, and the secretion again commenced. The explana- 

 tion which we are inclined to give of these facts is that at 

 first the casca, by causing contraction of the vessels generally, 

 and raising the blood-pressure, increases the pressure in the 

 glomeruli of the kidney, and thus causes the watery con- 

 stituents of the blood to filter through them more quickly than 

 usual. It thus increases the flow of urine. It next causes the 

 vessels of the kidney to contract more and more, so that 

 notwithstanding the high blood -pressure in the arterial system 

 generally, there is little blood in tlie kidneys. The pressure of 

 blood in the glomeruli is consequently low, and the secretion of 

 urine scanty, and when the contraction of the renal artery 

 becomes very great the secretion stops altogether. When the 

 arterial spasm again reiaxeS; the secretion recommences at the 

 same time that the blood- pressure falls. In this respect the 

 action of casca agrees completely with that of digitalis.* It 

 seems probable that casca will also, like digitalis, be found to 

 have a cumulative action, should it be introduced into medicine ; 

 for the effect of any drug depends on the amount of it cir- 

 culating in the blood, and this amount may be increased 

 either by increasing the introduction of new quantities or by 

 diminishing the excretion. It seems probable that the sudden 



* Brunton and Power, '' On the Diuretic Action of Digitalis." Froceedmgs 

 of the R >i/al Hocieti/, 1874, No. 153. Vide anlea, p. 410. 



