KIDNEY AND SKIN AS EXCRETORY ORGANS. 839 



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. 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 capa- 

 ble of excreting indigo-carmin after this substance is injected into 

 the blood. His experiment consisted 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 precipitate the indigo-carmin in situ in 

 the organ. Microscopical examination showed that after this 

 treatment the granules of the indigo-carmin are found in the con- 

 voluted tubules, but not in the capsules around the glomeruli. 



(3) Microchemical staining reactions have been used by several 

 observers to show that salts foreign to the blood, such as the 

 iodids and ferrocyanids, are excreted through the convoluted 

 tubules and not through the glomerulus. Recently Leschke * has 

 demonstrated by similar staining reactions that urea, uric acid, 

 sodium chlorid, and sodium phosphate are all eliminated through 

 the epithelium of the convoluted tubules. Each of these sub- 

 stances, when introduced into the blood, could be detected in 

 concentrated form in the cells of the convoluted tubules, while 

 no evidence of their presence in the glomeruli could be obtained. 



(4) Several observers (Van der Stricht, Disse, Trambasti, Gur- 

 witschf) 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 indi- 

 cate the discharge of these vesicles into the cavity of the tubules. 



(5) 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 deprived 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. These results, although denied 

 at one time, have later been confirmed and extended. J (6) 



* Leschke, "Zeitschrift fur klinische Medizin," 81, 14, 1914. 

 t See Gurwitsch, "Archiv f. die gesammte Physiologic," 19, 71, 1902. 

 j Bainbridge and Beddard, "Journal of Physiology," 1906, xxxiv. (Proc. 

 Physiol. Soc.); also Cullis, ibid., p. 250. 



