1070 



EXCRETION 



injecting oil into the circulation, but since oil embolisms were then also 

 found in the blood-vessels of the tubules, this method yielded no positive 

 results, although it was evident that the tubular vessels ridded them- 

 selves of these embolisms much sooner than the glomerular vessels. 

 Indigo-carmine injected at this time found its way in increasingly small 

 quantities into the urine, indicating thereby a gradual opening up of 

 the cells lining the convoluted tubules. The opposite condition may 

 be produced in rabbits by means of sodium tartrate which substance 

 gives rise to an inflammation or nephritis of the tubule. 1 If a solution 



of sodium chlorid and urea is then injected 

 into the circulation, the chlorin enters the 

 urine but not the urea. Obviously, the urea 

 is ordinarily secreted by the lining cells of the 

 tubule and not by those of the glomerulus. 



Fourthly, the secretory character of the 

 tubular epithelium may be established as 

 follows: In the frog it is possible to render 

 either the glomerular or the tubular segment 

 of the urinary tubule bloodless, because the 

 kidney of this animal receives a double blood- 

 supply. The one from the renal artery nour- 

 ishes the glomerulus and the one from the 

 renal portal vein, the tubule. Nussbaum 2 

 has shown that the ligation of the renal 

 artery greatly diminishes the flow of urine. 

 If urea is now injected into the dorsal lymph 

 sac of this animal, a very considerable amount 

 of this substance may be removed from the 

 urine. Obviously, therefore, the urea must 

 have found its way through the cells of the 

 tubules. The successful outcome of this ex- 

 periment requires a constant supply of oxygen 

 in order to retain these cells in a proper con- 

 dition of activity. This end can be accom- 

 plished by placing the frog in an atmosphere of oxygen. Contrariwise, 

 sugar, peptone and egg-albumin, when injected into the blood-stream, do 

 not enter the urine under these circumstances. These results have in 

 the main been confirmed by Beddard. 3 In addition, it has been shown 

 that the cells of the convoluted tubule eventually degenerate when 

 supplied only with renal-portal blood, because this blood is deficient 

 in oxygen. The stimulating action of this gas upon the secretory 

 power of the renal cells is also indicated by the experiments of Collis, 4 

 which show that the perfusion of the frog's kidney with non- 



1 Underbill, Wells and Goldschmidt, Jour, of Exp. Med., xviii, 1913, 347. 



2 Von Fiirth, Ergebn. der Physiol., 1902, 395. 



3 Jour, of Physiol., xxviii, 1902, 20. 



4 Ibid., xxxvii, 1908, 8. 



FIG. 525 . S E c T i o N 

 THROUGH THE CONVOLUTED 

 TUBULE (FROG) AFTER IN- 

 JECTION OF ToLurom. 



L, Lumen of tubule; C, 

 blood capillary. The lining 

 cells show blue pigment and 

 vesicles. 



