ACTION OF SALINE DIURETICS 707 



of their absorption. And again there is no experiment which 

 proves finally which of the two explanations is correct. 



The investigation of the action of diuretics other than saline 

 has failed to throw much light on the secretion of urine. Phillips 

 and Bradford found that when J or J grain of cafTein citrate is 

 injected into a vein the kidney volume shrinks for several minutes, 

 and the flow of urine is checked entirely or in part. This con- 

 striction of the kidney is followed by a marked and persistent 

 expansion, which is accompanied by a considerable diuresis. These 

 vascular changes occur after section of the splanchnics, and seem 

 to be of peripheral origin. The general arterial blood pressure 

 undergoes after an initial fall lasting but a few seconds a rise 

 to about normal ; it therefore cannot cause the changes in kidney 

 volume. Gottlieb and Magnus also, have found that the kidney 

 volume and diuresis caused by the injection of caflein or diuretin 

 run a more or less parallel course. Nevertheless it is probable 

 that the changes in renal circulation do not cause the alterations 

 in the secretion of urine. For, Phillips and Bradford noticed that 

 after cafTein injections the dilatation of the renal vessels might 

 occur without any diuresis. And Gottlieb and Magnus were able 

 to confirm Schroeder's statement that by the injection of chloral 

 hydrate it is possible to replace the expansion of the kidney 

 volume by an enormous shrinkage, and yet the diuretic effect of 

 cafTein may be observed. CafTein must therefore have a diuretic 

 action quite apart from any changes it produces in the renal circu- 

 lation, but whether it causes paralysis of absorption or a stimu- 

 lation of secretory activity is unknown. 



Phillips and Bradford investigated also the diuretic action of 

 digitalin and strophanthin. They found that an injection of 

 digitalin causes a slight but persistent rise in the general arterial 

 blood pressure, due partly to increased force of the heart- beat 

 and partly to peripheral vaso-constriction. The kidney volume 

 undergoes a considerable diminution synchronous with the vaso- 

 constriction, which may last half-an-hour ; this shrinkage is not 

 followed by an expansion, as it is after cafTein. The flow of urine 

 is not decreased, and may even be slightly increased during the 

 period of renal vaso-constriction ; this, again, is unlike the effect 

 produced by cafTein alone, but like the combined action of cafTein 

 and chloral. This slight diuresis after digitalin, in spite of renal 

 vaso-constriction, might be explained by an increased arterial blood 



