448 



PHYSIOLOGY 



CHAP, 



which depend on variations of vascular tonicity (Traube-Hering 

 waves of blood.-pressure curves), but run in the opposite direction. 

 This signifies that the volume of the kidney diminishes when the 

 general arterial pressure rises, and increases when that falls, 

 because the rise of pressure is due to constriction of the peripheral 

 arteries, in which the renal arteries also take an active part. 



This phenomenon can easily be produced artificially by 

 arresting artificial circulation in a curarised animal during the 

 experiment. The progressive asphyxia, which produces a diffuse 

 constriction of the small arteries and rise of general arterial 



ff 



FIG. 119. Roy's oncograph for recording alterations in the volume of an organ. Half the proper 

 size. The faintly traced tube K is connected with the oncometer by a nibber tube. 1> is a 

 piston resting on the oil contained in the cavity Af. The oil cannot escape at the sides since 

 it is confined by a thin, flexible membrane E, which does not interfere with the up-and-down 

 movement of the piston. The recording line H is connected with the piston by the n>-' 

 which works through F, F. The screw C clamps the membrane near the piston between the 

 two ring-shaped surfaces N. The side-tube L which carries a tap is used for filling 

 api>aratus with oil. 



pressure, causes a diminution in the volume of the kidney, becai 

 the renal vessels which participate in this constriction confine the 

 range of the renal circulation (Fig. 120). The same fact is 

 observed on stimulating the vasomotor centre in the bulb of 

 curarised animals, as well as on stimulating the splanchnics which 

 contain constrictor fibres for the renal arteries (Fig. 121). 



On repeating these experiments after section of the branches 

 of the renal plexus by which the vaso-constrictors penetrate, the 

 opposite result is obtained, i.e. increase of kidney volume from the 

 passive dilatation of the renal arteries, due to the rise of arterial 

 pressure. 



The vaso-constrictors of the kidney arise mainly in the dorsal 

 tract of the cord. In the dog the anterior "spinal roots from 



