ACTION OF SALINE DIURETICS 703 



tion, and found that the diuresis and increase in kidney volume 

 were coterminous, and that both might considerably outlast the 

 plethora. It was, therefore, clear that besides the plethora there 

 was some local action on the kidney causing both dilatation of 

 its blood-vessels and diuresis. In order to decide whether the 

 diuresis was caused by the local vaso-dilatation or was independent 

 of it, he injected dextrose and allowed blood to escape from the 

 carotid artery at a rate sufficient to keep the kidney volume from 

 expanding ; he then found that no diuresis was produced. He 

 concluded that the diuretic effect of these substances was due to 

 the vascular changes induced by them, and was not due to their 

 stimulating secretory cells ; a conclusion which is further sup- 

 ported by the fact that the diuresis ceases before the excretion 

 of the injected substance has come to an end. He ascribed the 

 diuresis to two factors, (a) hydraemic plethora, and a consequent 

 rise in a pressure and velocity of blood in the kidneys j and 

 (6) a direct dilator effect of the injected substance on the renal blood- 

 vessels which helped to increase capillary blood pressure and so 

 filtration. This conclusion seems to be supported by two other 

 observations. Saline diuresis is promptly stopped by the vaso- 

 constriction of the renal arterioles, which is caused by an injection 

 of suprarenal extract. Also caffein diuresis only takes place when 

 the kidney volume is increased. The first effect of an injec- 

 tion of caffein is to decrease the kidney volume by vaso-constric- 

 tion of peripheral origin, and during this stage little or no urine is 

 excreted. 



Gootlieb and Magnus subsequently investigated the subject, 

 and agreed with Heidenhain's explanation. They found, like 

 Starling, that an increased kidney volume generally accompanies, 

 but denied that it caused the diuresis. For they observed that 

 the diuresis outlasted the increase in volume, and might even 

 take place with a shrinkage of the kidney. And Thompson from 

 his experiments came to the same conclusion. They further 

 objected that in Starling's bleeding experiment the loss of blood 

 necessary to keep the kidney volume from expanding was such 

 that the aortic pressure was thereby reduced to about 60 mm. Hg., 

 and therefore invalidates the conclusion which Starling drew 

 from the experiment. For, with such an aortic pressure, even on 

 Heidenhain's view it could not be expected that the diuretic would 

 have anything like the effect which it would have wh,en the, 



