CHAP, iv.] RENAL SECRETIOtf. 403 



continue when the blood-pressure sinks even below this point. 

 Section of the spinal cord in the dorsal region similarly depresses 

 the general blood-pressure and similarly arrests or diminishes the 

 secretion of urine. This is an operation however from which an 

 animal may, if duly tended, recover, and live for a long time with 

 the lumbar spinal cord quite separated from the brain and upper 

 parts of the spinal cord. In such a case the secretion of urine is 

 soon re-established; but the general blood-pressure is also re- 

 established, so that this condition of things also illustrates the 

 connection between blood-pressure and the secretion of urine. 



Stimulation of the spinal cord below the medulla, though acting 

 in the converse direction, brings about the same result, arrest of 

 the secretion. By the stimulation the action of the vaso-motor 

 nerves is augmented, and constriction of the renal arteries as well 

 as of other arteries in the body is brought about. The increase of 

 general blood-pressure thus produced is insufficient to compensate 

 for the increased resistance in the renal arteries; and as a con- 

 sequence the flow of blood into the glomeruli is largely reduced. 

 We have seen that under these circumstances the kidney shrinks, 

 and indeed on inspection it is seen to become during the stimu- 

 lation pale and bloodless. 



Section of the renal nerves is followed by a most copious 

 secretion, by what has been called hydruria or polyuria. The 

 section of the nerves, by interrupting the vaso-motor tracts, even if 

 it does not act in the way of destroying a normal tone (the existence 

 of which seems doubtful), prevents the advent of ordinary con- 

 stricting impulses, and thus indirectly leads to dilation of the renal 

 arteries, and so to increased pressure in the small vessels of the 

 glomeruli. If, after section of the renal nerves, the cord be divided 

 below the medulla, the polyuria disappears ; for the diminution of 

 general blood-pressure thus produced more than compensates for 

 the special dilation of the renal arteries. Conversely, if after 

 section of the renal nerves the cord be stimulated, the flow of urine 

 is still further increased, since the rise of general blood-pressure due 

 to the general arterial constriction caused by the stimulation tends 

 to throw still more blood into the renal arteries, on which, owing 

 to the division of their nerves, the spinal stimulation is powerless. 

 The section of the renal nerves sometimes leads to the appear- 

 ance of albumin in the urine, but this is probably due to some 

 other effects than those of variations in blood-pressure simply. 



Section of the splanchnic nerves produces also an increased flow 

 of urine. But the augmentation in this case is smaller and less 

 certain than in the case of section of the renal nerves themselves, 

 partly because the vaso-motor tracts from the spinal cord to the 

 kidneys do not run exclusively in the splanchnic nerves but reach 

 the kidney along some other path or paths, and partly because the 

 splanchnic nerves govern the whole splanchnic area, and hence a 

 large portion of the increased supply of blood is diverted from the 



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