THE SECRETION OF URINE 1069 



reference should also be made to the action of adrenalin which 

 stops the secretion of urine in spite of the fact that it heightens the 

 blood pressure. This discrepancy, however, is only an apparent one, 

 because upon its entrance into the kidneys, this agent constricts the 

 local blood-vessels and gives rise to an anemia which effectively blocks 

 the activity of these cells. 



Secondly, it might be mentioned that a certain secretory resistance 

 does not retard the function of the renal cells but actually stimulates it. 

 While it is true that urine is formed under a glomerular pressure of 

 from 40 to 60 mm. Hg and a ureter pressure of about zero, the latter 

 may be heightened considerably before the cells actually cease their 

 function. The upper limit is reached at about 60 to 80 mm. Hg, i.e., 

 at a pressure less than half of that necessary to stop the secretion of 

 saliva. The reason for their inability to raise the urinary pressure 

 more decidedly above that prevailing in the capillaries, is due in 

 largest part to the early occurrence of hydremia which indicates that 

 the watery constituents of the urine escape into the interstitial spaces 

 and are reabsorbed. Slight increases of the urinary pressure, on the 

 other hand, invariably augment the activity of these cells. 



Thirdly, mention should be made of those experiments which 

 jointly establish the fact that the epithelial lining of the urinary tubules 

 possesses true secretory properties. Heidenhain first attempted to 

 prove this positively by injecting coloring material into the blood-stream 

 of rabbits and demonstrating its presence in the cells of the urinary 

 tubule by histological means. In order to eliminate the factor of 

 pressure as much as possible, the spinal cord was cut previous to the 

 injection. The vascular relaxation then ensuing gave rise to so low 

 a blood presssure that practically no fluid came down the tubules. 

 In all these cases, the indigo-carmine appeared in the form of blue 

 granules within the cytoplasm of the rodded epithelium, lining the con- 

 voluted tubules and ascending limb of the loop of Henle, but not in 

 the cells of the glomeruli. In fact, some of these granules could also 

 be detected in the lumen of the urinary tubule This was invariably 

 the case in all those animals whose spinal cord had not been divided 

 before the injection. Evidently, the retention of the vascular tonus 

 of the kidney tends to wash these granules rapidly out of the cells 

 into the secretory duct. 



More recently Schaffer^ has confirmed these results by means of 

 leuco-indigo-carmine, a colorless reduction derivative of indigo-car- 

 mine. This pigment remained colorless in the cells themselves, but 

 appeared in its oxidized (blue) form in the lumen of the tubule. It 

 could not be detected in the capsule of Bowman. Heidenhain has also 

 shown that urate of soda is excreted by the lining cells of the tubules. 

 In attempting to prove that the glomerulus acts independently of the 

 convoluted tubule, Lindemann^ sought to isolate this structure by 



1 Am. Jour, of Physiol., xxii, 1908, 323. 



2 Zeitschr. fiir Biol., xlii, 1902, 161. 



