CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 663 



spoken of as the vaso-constrictor region of the spinal cord. They 

 issue from the spinal cord by the anterior roots of a large number 

 of the spinal nerves taking origin from this region, and may be 

 traced (in the dog) as high up as the 6th dorsal, a few perhaps 

 even to the 4th dorsal, and as low down as the 2nd lumbar (4th 

 lumbar if only 13 nerves be counted as dorsal) ; but most seem to 

 pass by the llth, 12th and 13th dorsal nerves. Passing through 

 the corresponding ganglia of the splanchnic (sympathetic) chain, 

 these fibres reach the solar plexus and thus the renal plexus by 

 the abdominal splanchnic nerve ; those however coming from some 

 of the lower nerves apparently do not contribute to the splanchnic 

 nerve, but take a separate course. Centrifugal stimulation of 

 these anterior roots produces shrinking of the kidney, all the more 

 marked and distinct in the case of the llth, 12th and 13th dorsal 

 roots because the effect on the kidney is then riot so much masked 

 by vaso-motor effects on other organs. Stimulation of the higher 

 roots also produces shrinking of the kidney but less marked, since 

 in these cases the stimulation bears at the same time largely on 

 vaso-constrictor fibres for other abdominal organs, and so by raising 

 the general blood -pressure tends to neutralize the local effect on 

 the kidney. And even the very decided shrinking of the kidney 

 which results from the stimulation of the splanchnic trunk itself 

 is less than would take place if the stimulation affected the vessels 

 of the kidney only. 



413. We stated in 168 that by the method of slowly 

 repeated rhythmical stimulation the presence of vaso-dilator fibres 

 in the sciatic nerve might be detected, though these are largely 

 mixed with vaso-constrictor fibres ; and slow rhythmical stimu- 

 lation of the anterior roots of the above-mentioned lower dorsal 

 nerves leads, not, as does ordinary rapidly interrupted stimulation, 

 to shrinking, but to swelling of the kidney, shewing that these 

 roots contain vaso-dilator fibres as well as vaso-constrictor fibres. 

 The higher (anterior) roots also appear to contain some renal 

 vaso-dilator fibres ; but the effect of stimulating them by the 

 slow rhythmic method is more masked by a concomitant dilation 

 of the vessels of the other abdominal organs, the roots in 

 question containing vaso-dilator as well as vaso-constrictor fibres 

 for those organs ; this leads to a fall of general blood-pressure 

 whereby the tendency of the kidney to swell is counteracted. As 

 far as can be ascertained at present the paths of the renal vaso- 

 dilator fibres are similar to those of the renal vaso-constrictor 

 fibres. 



The kidney then is well supplied, especially through the 

 anterior roots of the llth, ]2th and 13th dorsal nerves, with 

 \, i s ( (-constrictor fibres, and is also supplied with vaso-dilator fibres. 

 Some results have seemed to shew that the fibres passing along 

 the roots of one side of the spinal cord govern the vessels 

 not only of the kidney of the same side but also to a certain 



