KIDNEY AND SKIN AS EXCRETORY ORGANS. 747 



what indirect; a single example may suffice. Cushny states* that 

 if certain diuretics for example, sodium chlorid and sodium sul- 

 phate are injected simultaneously into the blood and in such 

 amounts that an equal number of the anions (CI and S0 4 ) are pres- 

 ent, the quantities that are excreted in the urine during the next 

 hour or two follow different curves and vary independently of their 

 concentration in the plasma. While this independence might be 

 referred to a specific secretory action, the author finds a simpler 

 explanation in variations in absorption, the epithelium of the con- 

 voluted tubule, like that of the intestine, absorbing the sulphate 

 with more difficulty. On the other side, the facts that have been 

 urged in favor of the secretory hypothesis are more numerous and 

 varied, but none is entirely convincing. Some of these facts are 

 as follows: (1) It is stated that if the ureters are ligated in birds 

 the urates will be found deposited in the uriniferous tubules, but 

 never at the capsular end. (2) Heidenhain has given proof that 

 the convoluted tubules are capable of excreting indigo-carmin after 

 this substance is injected into the blood. His experiment consisted 

 essentially in injecting the material into the blood, after dividing 

 the cord so as to reduce the rapidity of secretion. After a certain 

 interval the kidney was removed and irrigated with alcohol to pre- 

 cipitate the indigo-carmin in situ in the organ. Microscopical ex- 

 amination showed that after this treatment the granules of the 

 indigo-carmin are found in the convoluted tubules, but not in the 

 capsules around the glomeruli. (3) Several observers (Van der 

 Stricht, Disse, Trambasti, Gurwitschf) have described microscopical 

 appearances in the cells lining the tubules indicative of an active 

 secretion. They picture the formation of vesicles in the cells and 

 appearances which indicate the discharge of these vesicles into the 

 cavity of the tubules. (4) Nussbaum made use of the fact that in 

 the frog the glomeruli are supplied by branches of the renal artery, 

 while the rest of the tubes are supplied by the renal portal vein. 

 He stated that if the renal artery is ligated the glomeruli are de- 

 prived completely of blood, and that as a result the flow of urine 

 ceases. If under these conditions urea is injected into the circulation 

 it is excreted together with some water, thus proving the secretory 

 activity of the tubules with regard to urea. Later experiments by 

 Adami and by Beddard % have thrown doubt upon this otherwise 

 crucial experiment. Adami claims that ligature of the renal arte- 

 ries does not shut off completely the glomerular circulation, while 

 Beddard, although he corroborates Nussbaum in the point that 

 complete occlusion of the renal arteries suspends entirely the secre- 



* "Journal of Physiology," 27, 429, 1902. 



t See Gurwitsch, " Archiv f. die gesammte Physiologie, " 91, 71, 1902.- 



t Beddard, " Journal of Physiology, " 28, 20, 1902. 



