677 



serum to pass, which as we observed before^) is not a strict proof 

 that sugar cannot be present in a coni})Osition with a senim-compoLind 

 which can pass through these two membranes, but not through the 

 glomerulus-epithelium. Now, however, it has been demonstrated that 

 the glomerulus epithelium can keep back the ghicose as such. 



We have evidently to deal here with a Jieiv form 0/ permeability: 

 cells, here the glomerulus-epithelium, allow salts to pass, but not 

 the likewise crystalloid sugar, which under the circumstances is 

 highly useful; for thus a substance necessary for our nutrition is 

 kept in circulation. As far as we can see we find ourselves con- 

 fronted here by a phenomenon not observed before. The intestinal 

 epithelium and likewise the pleura and the peritoneum are perme- 

 able to salts as well as to glucose; the red blood-corpuscles of most 

 animals are impermeable to salts and to sugar both "). 



Finally we wish to point out another fact. An examination of 

 table III makes it evident that although the transmission-fluid con- 

 tained neutral red, mostly a colourless urine was obtained in these 

 cases, therefore, the neutral red had been kept back by the glome- 

 rulus-epithelium. That the urine was free from neutral red appeared 

 from the fact that neither the addition of acid nor that of alkali 

 to the urine caused colouring. 



Hence we may assume that if the NafTCOa concentration is high 

 enough, the glomerulus-membrane is impermeable to the colloid 

 neutral red. If the NaHCOg cone, amounts to only 0.02 7o then the 

 glomerulus-filtrate becomes red, because the RiNGER-fluid, on being trans- 

 mitted, grows too acid. That this is really only a glomerulus-product 

 appears when for instance the porta renalis is ligatured, for then the 

 urine-secretion through the tubulus epithelium is prevented fcf. our 

 first publication) '). According to table 111, however, the urine in 

 some of these .experiments was yellow, but this colouiing originated 

 from neutral red, which is excreted by the tubulus epithelium ; this 

 is confirmed by the experiments of Höber and Königsberg, to which 

 we shall have to refer again presently. 



Our experiments also throw a light on the contradiction between 

 the results of the experiments of Gerzovvitsch ^) and those of Höber ^). 



') Cf. our first paper in Verslagen Jan. 1917. 



2) Only some blood-corpuscles viz. those of man, of the monkey and of the dog 

 seem, to a certain extent, permeable to sugar. 



3) Meeting of January 27, 1917. 



^ *) Gerzowitsch: Zeitschr f. Biologie, 66, 391, (1916). 



5) Höber und Königsberg: Pflügers Archiv 108, 324. (1905). 



49 

 Proceedings Royal Acad. Amsterdam. Vol. XX 



