4 68 TEXT-BOOK OF PHYSIOLOGY 



tube from the pressure bottle is closed, the conditions are such that all varia- 

 tions in the volume of the kidney are taken up and reproduced by the level 

 attached to the piston recorder. A curve of the variations in the volume 

 of the kidney is shown in Fig. 213. An examination of this curve shows thai 

 the volume-changes exhibit not only the respiratory but also the cardiac 

 undulations. 



The Influence of the Nerve System. The influence of the nerve system 

 in regulating the blood-supply to the kidney is evident from the results oi 

 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 induced electric currents the artery contracts, the kidnej 

 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-dilata- 

 tor nerves. The vaso-constrictor nerves 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 the centers of origin 

 of these nerves gives rise to contraction or to a dilatation of the artery, a 



FIG. 213. CURVE OF THE VARIATIONS IN THE VOLUME OF THE KIDNEY. 



diminution or a swelling of the kidney, and a decrease or an increase in 

 secretion, independent of any variation in general blood-pressure according 

 to the nature of the cause acting. 



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

 the lesser splanchnics, the terminal branches of which arborize around the cells 

 of the renal ganglia; from these ganglia new fibers arise which pass through 

 the renal plexus into the kidney to be distributed to the muscle coat of the 

 renal artery branches. 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 vaso-motor center for the blood-vessels of the kidney is in all proba- 

 bility situated in the medulla oblongata in close proximity to the general 

 vaso-motor centers, though subordinate centers are doubtless present in the 

 spinal cord. It was found by Bernard that puncture of the medulla was 

 occasionally followed by a profuse secretion of urine without the presence 

 of sugar. The route of the vaso-motor impulses which influence the renal 

 blood-supply is down the cord to local vaso-motor centers, thence through the 

 splanchnics to the renal ganglia, thence through the renal plexus to the 

 blood-vessels. 



