368 The Innervation of ike Renal Blood-vessels. [Feb. 21, 



is not altogether to be explained as resulting simply from the height- 

 ened blood pressure, since an equal rise, produced say by the sciatic 

 and accompanied by contraction of the renal vessels, is not followed 

 by this profuse haemorrhage. Hence it is probable that not only is 

 there a dilatation of the kidney vessels, but also of the vessels in the 

 lumbar region of the body wall, hence the haemorrhage. 



Rarely excitation of a posterior root causes a depressor effect, there 

 being a great fall of blood pressure, and then as usual the kidney 

 undergoes a passive contraction, owing to the large dilatation else- 

 where. 



The results of reflex excitation can then be summed np shortly by 

 saying that the excitation of an afferent nerve causing a rise of blood 

 pressure is accompanied by a renal contraction, unless the nerve is one 

 of what may be called the renal area. In this case the rise of blood 

 pressure is accompanied as a rule by either a renal expansion or else 

 by a mixed kidney effect. If the afferent nerve causes a depressor 

 effect due to dilatation of the abdominal vessels, the kidney vessels 

 probably share in that dilatation, but this is not seen by any actual 

 renal expansion owing to this being overpowered by the dilatation 

 elsewhere, and hence the kidney undergoes a passive shrinking. 



The other conclusions of this paper are that the renal constrictor 

 fibres leave the cord through the anterior roots of the nerves extend- 

 ing from the 6th dorsal to the 2nd lumbar inclusive. 



That, secondly, there are vaso-dilator fibres, as can easily be demon- 

 strated with such nerves as the llth or 12th dorsal, but that in all 

 probability they also extend from the 6th dorsal to the 2nd lumbar, 

 and for the reasons given above they cannot be demonstrated with 

 certainty in the upper nerves, since here they run with the vaso- 

 dilator fibres for the vessels of the other abdominal viscera. 



Hence there is no evidence to show that the vaso- constrictor fibres 

 and the vaso-dilator fibres reach the kidney by different routes. 



Finally, the great splanchnic nerve contains not only vaso-con- 

 strictor, but also vaso-dilator fibres, for the vessels of the abdominal 

 viscera. 



The expenses of this research were partly defrayed by a grant 

 obtained from the Royal Society. 



