432 TEXT-BOOK OF PHYSIOLOGY. 



the kidney, as well as the tube leading to the chamber of the onco- 

 graph, are completely filled. When the tube I is closed, the condi- 

 tions are such that all variations in the volume of the kidney are 

 taken up and reproduced by the recording lever attached to the 

 piston of the oncograph. A curve of the variations in the volume 

 of the kidney is shown in figure 198, taken simultaneously with the 

 curve of the blood-pressure. An examination of this curve shows 

 that the volume-changes coincide with changes in the blood-pressure, 

 exhibiting not only the respiratory but also the cardiac undulations. 

 Influence of the Nervous System. The influence of the 

 nervous system in regulating the blood-supply to the kidney is evi- 

 dent from the results of experimentation. If the nerves which 

 accompany the renal artery into the kidney are divided, the artery 

 at once dilates, the kidney enlarges, and a copious flow of urine 

 takes place. If the peripheral ends of these nerves be stimulated 

 with the induced electric current, the artery contracts, the kidney 



B.P. 



FIG. 198. B. P. Blood-pressure curve. K. Curve of the volume of the kidney. T. 

 Time curve; intervals indicate a quarter of a minute. A. Abscissa (Stirling, 

 after Roy.) 



diminishes in size, and the flow of urine ceases. In addition to 

 these vaso-constrictor nerves, there is evidence that the kidney also 

 receives vaso-dilator nerves which emerge from the spinal cord and 

 are found in the anterior roots of the eleventh, twelfth, and thirteenth 

 dorsal nerves, in the dog. Direct and reflex stimulation of these 

 nerves gives rise to a dilatation of the artery, a swelling of the 

 kidney, and an increase in secretion, independent of any variation 

 in general blood-pressure. 



The route of the vaso-constrictor nerves is, in the dog at least, 

 through the splanchnics. Section of these nerves is followed by a 

 dilatation of the renal vessels and an increase in the flow of urine. 

 Stimulation of the peripheral ends is followed by a constriction of 

 the vessels and a cessation of the flow of urine. 



The vasomotor center for the blood-vessels of the kidney is in all 

 probability situated jMfe medulla oblongata in close proximity to 

 the general vasomotor centel : s7th^ug^rsur5ordinate centers are doubt- 



