94 THE INVOL UNTA R Y NER VO US S YSTEM 



decided dilatation of the kidney occurred without any rise of 

 blood pressure and often without any appreciable fall. He con- 

 cluded, therefore, that vaso-dilator nerves to the renal blood 

 vessels exist and take the same paths as the vaso-constrictors. 



Further, he found that stimulation of the peripheral end of 

 the splanchnic nerve with the same slow rhythmical stimulation 

 always caused a fall of blood pressure instead of the marked rise 

 so well known upon ordinary faradic stimulation. This occurred 

 quite markedly when the splanchnic nerve was stimulated above 

 the entrance of the ramus communicans from the eleventh 

 thoracic nerve, and as the presence of vaso-dilator nerves for the 

 kidney could not be shown in the anterior roots of the sixth to 

 tenth thoracic nerves, it is clear that this fall of blood pressure 

 must be due to dilatation of blood vessels of the abdominal area 

 other than those of the kidney. Bradford therefore concludes 

 that the vascular area, supplied by the splanchnic nerve, receives 

 both vaso-constrictor and vaso-dilator fibres, which pass out from 

 the cord in the same anterior roots. These conclusions of Brad- 

 ford have been confirmed by Dale, who has found that, after 

 ergotoxine, stimulation of the anterior roots of the eleventh and 

 twelfth thoracic nerves causes a dilatation of the renal vessels instead 

 of a constriction ; and stimulation of the splanchnics causes a fall 

 instead of a rise of blood pressure. 



It is difficult to ascribe this vascular dilatation to the action 

 of metabolites produced by the activity of the kidney, for 

 there is no evidence for the existence of nerves which cause 

 secretion in the kidney. At the same time there is some evi- 

 dence that, when the kidney is made to excrete by the presence 

 of urea, its blood vessels are dilated. Roy showed that injec- 

 tion of urea into the blood caused not only a secretion of urine, 

 but also a dilatation of the kidney vessels, even when all the 

 nerves going to the kidney were cut. Seeing that urea in- 

 jected into the blood flowing through an organ will not cause 

 dilatation of the blood vessels of that organ, but does produce 

 dilatation in the kidney vessels, it follows that such dilatation is 

 a consequence of the activity of the kidney cells excited by the 

 presence of urea, and can be explained in the same way as the 

 dilatation which occurs in the submaxillary gland or in active 

 muscle. 



Finally, we come to the question of the causation of erection. 



