PHYSIOLOGICAL PROCESS OF URINARY SECRETION 511 



of fluid accordingly can not take place from the true renal capillaries, because 

 the blood-pressure in these must be increased by occlusion of the veins, and this 

 would cause increased nitration. On the other hand, the observation mentioned 

 would indicate that the secretion takes place from the capillaries of the glomerulus. 

 The venous stasis in the efferent vessel distends this vessel, which arises in the 

 center of the convolution, to such a degree that the capillary loops are pushed 

 together against the wall of the capsule and compressed, so that no nitration can 

 take place from them. Whether some fluid is given off through the urinary 

 tubules, especially the convoluted tubules, is as yet undecided. 



The amount of urine and the amount of contained urea are diminished by 

 venous stasis in the kidneys. The amount of sodium chlorid remains constant, 

 while that of albumin in pathological urine increases. 



As the blood-pressure in the renal artery equals between 120 and 

 140 mm. of mercury, and the urine in the ureter is propelled under 

 exceedingly slight pressure, so that it is no longer capable of escaping 

 against a counter-pressure of from 10 to 40 mm. provided by a manome- 

 ter introduced into the ureter divided transversely it must be clear that 

 the blood-pressure is also capable, as a vis a tergo, of forcing the stream 

 of urine through the ureter. 



The degree of concentration of the urine depends upon the amount 

 of the constituents in solution passing out of the blood into the 

 urinary water. The cells of the convoluted urinary tubules appear to 

 take up these substances from the blood by means of an independent 

 activity. The urinary water passing through the urinary tubules from 

 the glomerulus, and containing only readily diffusible salts, later takes 

 up these substances out of the cells of the convoluted tubules by a pro- 

 cess of extraction. The independent activity of the cells is indicated 

 by the following facts : 



i. Sulphindigotate of sodium (indigocarmin), which, when injected 

 into the blood, passes into the urine, can be recognized in the interior of 

 the cells of the urinary tubules, but not in the capsules. Further on, 

 this substance is visible in the lumen of the urinary tubules, whither it 

 is washed by the current of urinary water from the glomerulus. If, 

 in such an experiment, the cortical layer containing the capsules has 

 been removed two days previously by cauterization or with the knife, 

 the blue pigment will have remained in the convoluted tubules. It 

 will not have advanced onward, as the current of water from the de- 

 stroyed glomeruli is wanting. This observation thus indicates that 

 the glomeruli furnish principally the urinary water, and the convoluted 

 tubules the specific urinary elements. Heidenhain and Sauer observed 

 also urates (injected into the blood) secreted by the convoluted tubules. 

 Nussbaum has also demonstrated that urea is not secreted by the cap- 

 sules, but by the urinary tubules. Mobius found the same with respect 

 to the biliary pigment, Glaevecke with respect to the iron salts of the 

 vegetable acids when injected subcutaneously, and Landois first 

 described the same condition with respect to hemoglobin. After in- 

 fusion of milk into the vessels, Landois encountered numerous fat- 

 globules within the cells of the urinary tubules. 



It appears that the capsules may also take part in the process only after 

 abundant secretion. After infusion of large amounts of sodium sulphindigotate 

 and after the observation has been continued for some time, the epithelium of the 

 Malpighian capsules also exhibits the blue discoloration. Likewise in the presence 

 of albuminuria, the abnormal elimination of albumin takes place first in the urinary 

 tubules and later in the capsules. Also hemoglobin occurs in part in the capsules. 

 Egg-albumin is believed by Nussbaum to be excreted through the capsules. 



