532 FLOW OF BLOOD THROUGH KIDNEY. [Book ii. 



§ 335. If, while the kidney is in the oncometer, and the 

 various experiments on section and stimulation of nerves and 

 the like are being carried on, a cannula be tied in the ureter, the 

 secretion of urine may be watched at the same time. It will 

 then be seen that the Aoav of urine through the end of the 

 cannula is not equable, and does not either increase or decrease 

 in an even manner. On the contrary, it will frequently be 

 found that a sort of gush of urine takes place, several drops 

 following each other in rapid succession, followed by a cessation 

 of flow ; and if the ureter be watched it will be seen that the 

 gushes of urine are synchronous with waves of peristaltic con- 

 traction sweeping down the ureter. Obviously the urine collects 

 to a certain extent in the pelvis of the kidney and is driven 

 thence by muscular action from time to time ; to this point we 

 shall return later on. 



Making every allowance, however, for these irregularities of 

 flow, we may take the rate of flow from the end of the cannula 

 as a measure of the rate of secretion ; and it is found that as a 

 general rule increased flow of urine is coincident with swelling 

 of the kidney, that is with a greater flow of blood through it, 

 and diminished or arrested flow of urine is coincident with 

 shrinking of the kidney, that is with a diminished flow of blood 

 through it. 



A striking instance of this is afforded by the experiment of 

 dividing in the dog the spinal cord below the spinal bulb. The 

 blood-pressure then, as we know, falls rapidly, owing to the 

 removal of constrictor impulses from the small arteries and the 

 great diminution of peripheral resistance which follows upon 

 so many small arteries becoming dilated ; and though the renal 

 arteries probably share in the general relaxation yet, owing to 

 the fall of pressure in the aorta conjoined as this is by a corre- 

 sponding rise of pressure in the vena cava, the flow of blood 

 through the kidney is largely diminished. We find that after the 

 operation the secretion of urine is greatly diminished; indeed, 

 in most cases, the flow from the end of a cannula is almost 

 arrested. In fact we may almost make the general assertion that, 

 when in the dog the blood-pressure falls to about 30 mm. Hg or 

 less, the secretion of urine is for the time stopped. These and 

 other results support the view stated above that the secretion of 

 urine is in quite a special way dependent on the flow of blood 

 through the kidney ; and we may further conclude that the 

 secretion which is so particularly influenced by the flow of blood 

 is that special kind of secretion, allied to filtration, which takes 

 place through the glomeruli, and not the more ordinary kind of 

 secretion by means of the epithelium of the tubuli uriniferi. 

 But before we proceed to discuss how the increased flow of 

 blood increases the glomerular flow of urine, we must turn to 

 consider the functions of the epithelium of the tubuli. 



