1118 PHYSIOLOGY 



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

 placed in the carotid artery and connected with a mercurial mano- 

 meter, so that two tracings are obtained at the same time on the 

 moving blackened surface. In the figure given (Fig. 468), 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 at the point marked with a cross on the tracing. The peri- 

 pheral end of the anterior root of the tenth dorsal nerve was excited by 

 means of an interrupted current. 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 pressure 



FIG. 468. 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.) 



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 the arterioles of the kidney, emptying this organ of 

 blood and so causing it to decrease in size. This contraction of the 

 vessels would tend to cause a rise in general blood pressure and must 

 have taken some part at any rate in the rise actually observed. If the 

 oncpmeter in this experiment had been used alone, it would have 

 been impossible to have determined whether the shrinkage of the 

 kidney might not have been due to a lowering of general blood 

 pressure, in consequence of vase-dilatation occurring elsewhere, or in 

 consequence of the failure of the heart's activity. On the other hand, 

 wjrthout the oncometer it would only have been possible to determine 

 that there was increased peripheral resistance somewhere or other in 

 the body. 



