1036 



PHYSIOLOGY 



The kidney being placed in some such apparatus, a cannula is inserted 

 in the carotid artery and connected with a mercurial manometer, so that 

 two tracings are obtained at the same time on the moving blackened surface. 



FIG. 471. Diagram of Schafer's air plethysmograph. 



In the Figure given (Fig. 472), the upper curve represents the carotid blood 

 pressure, while the lower is the tracing of the oncograph lever. At the 

 beginning of the experiment the lower dorsal nerve roots had been dissected 

 out and prepared for stimulation. The peripheral end of the anterior root 



Blood pressure 



Kidney volume 



FIG. 472. Simultaneous tracings of carotid blood pressure and volume of kidney. 

 Between X and X the peripheral end of the divided tenth dorsal nerve was 

 stimulated. Time-marking = seconds. (BRADFORD.) 



of the tenth dorsal nerve was excited by means of an interrupted current 

 at the point marked with a cross on the tracing. This stimulation was 

 followed by a rise of blood pressure together with a diminution in the kidney 

 volume. The increased blood pressure would by itself tend to force more 

 blood into the kidney and so increase its volume. The fact that the kidney 

 volume diminished shows that there must have been active contraction of 



