EXCRETION. 483 



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 223 taken simul- 

 taneously 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. 

 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 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 induced electric currents the artery contracts, the kidney 

 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 which emerge from the spinal cord and are found in the anterior 



B.P. 



ney. 

 intervals indicate a quarter of a minute. A. Abcissa. (Stirling, after Roy.) 



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 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. 



Influence of Variations in the Composition of the Blood. As it is 

 the function of the kidneys to excrete water, inorganic salts, and various 



