viii THE EXCEETION OF UKINE 429 



The same effect is obtained by stimulation of the splanchnic, and 

 of the medulla oblongata or spinal cord (Eckhard), also by arrest 

 of the respiratory movements which produces asphyxia (Griitzner). 

 This operation, as we know, causes a conspicuous rise of aortic 

 pressure owing to diffused vaso-constrictor action ; but since the 

 branches of the renal artery also contract, the renal circulation is 

 diminished, not increased, consequently instead of a rise there is 

 a fall in urinary secretion. When, on the contrary, the splanchnic 

 and spinal cord are excited after division of the nerves of the renal 

 plexus on one side, there is marked acceleration of urinary secretion 

 on the side operated on, while in the other kidney it is entirely 

 arrested (Griitzner). 



These experimental facts as a whole seem at first sight to lend 

 substantial support to Ludwig's theory, . by which the renal 

 glomeruli are regarded as a mere filtering apparatus. In fact, when 

 blood pressure rises or falls in the renal artery (and therefore in 

 the glomeruli) the secretion of urine also must increase or decrease, 

 because the difference between .the glomerular and the capsular 

 pressure, which mechanically causes the phenomenon of filtration, 

 becomes greater in the first case and less in the second. To this 

 it may be objected that under all the experimental conditions 

 above described in which pressure was altered in the renal artery, 

 the velocity of the renal circulation was altered in the same 

 direction. Other experimental data tend to show that the renal 

 secretion depends not so much upon the pressure as upon the rate 

 at which the blood circulates in the kidneys. In fact, if a rise of 

 blood pressure be artificially produced in the kidneys together with 

 a delay or block in the current, there is no increase in the flow of 

 urine, but the exact opposite occurs, i.e. diminution or arrest of 

 the secretion. 



It has long been known that compression or ligation of the 

 efferent veins will ipso facto produce a decrease or arrest of the 

 urinary secretion (B. H. Meyer, 1844; Frerichs, 1851; Ludwig, 

 1856). 



According to Ludwig this fact does not contradict his filtration 

 theory, because the occlusion of the vas efferens produces such a 

 swelling of the interlobar and interlobular renal veins, that the 

 tubules which conduct the urine are compressed, and the flow of 

 urine from the papillae is impeded. This fact, however, might be 

 due to the arrest of the vascular circulation, which produces 

 asphyxia and alters the nutrition of the glomerular epithelium 

 as thought by Heidenhain (1883). In fact, when the vein is 

 freed and the circulation re-established, albumin uria sets in for a 

 certain time. In any case Ludwig's interpretation is not applicable 

 to the fact that simple constriction of the renal veins without 

 interruption of the circulation suffices to reduce the flow of urine 

 to a minimum (Senator, Paneth). The same result can also be 



