646 THE SECRETION OF URINE. 



division of all the renal nerves, stimulation of the cord causes a large 

 expansion of the kidney and brings back the urinary flow. 



Influence of the splanchnics. 1 The effects of stimulating the splanch- 

 nic nerves are very similar to those obtained from the stimulation of the 

 cord. As in the latter case, a large rise of general blood pressure is 

 produced, but the constriction of the renal vessels more than counteracts 

 the effects of this rise, so that the kidney shrinks and the flow of urine 

 is diminished or abolished. The effects of dividing the splanchnics vary 

 in different animals. In the rabbit, where, in consequence of the extent 

 of the vascular area supplied by this nerve, a considerable fall of general 

 blood pressure is produced, no increase in the urinary secretion is 

 observed. In the dog, on the other h^ad, the lasting effect on the aortic 

 pressure is insignificant, so that the relaxation of the kidney vessels 

 caused by the section induces a largely increased flow through this organ, 

 and a marked increase in the flow of urine. 



Influence of renal nerves. Division of the renal nerves on one side 

 causes vasomotor paralysis in the organ of that side. The kidney there- 

 fore swells, and the flow of urine is increased. The swelling and 

 secretion is still further increased if the general blood pressure be raised 

 by stimulation of the splanchnics or spinal cord. Stimulation of the 

 renal nerves causes constriction of the vessels and diminished flow of 

 urine. 



Bradford 2 has brought forward evidence to show that vaso -dilator 

 fibres run to the kidney with the constrictors, in the eleventh, twelfth, and 

 thirteenth dorsal nerve roots. If the anterior roots of these nerves be 

 stimulated with induction shocks, repeated at the rate of one per second, 

 the effect is often a marked swelling of the kidney without any rise of 

 blood pressure sufficient to account for the enlargement. A similar 

 active dilatation of the vessels may be brought about reflexly by stimulat- 

 ing the posterior roots of these nerves. We have no direct experimental 

 evidence as to the influence of this active vascular dilatation on the 

 renal secretion, although it is extremely probable that a similar condi- 

 tion is the chief factor in the production of the extreme hydruria met 

 with in hysteria and other nervous affections. 



Constriction of renal artery. In some of the earliest researches on the 

 connection between the blood flow through the kidney and the urinary 

 secretion, it was sought to affect the circulation by direct mechanical 

 constriction of the renal artery. Hermann, 3 who carried out experi- 

 ments of this nature under Ludwig's guidance, showed that when the 

 artery was constricted to a considerable extent, the result was a dimin- 

 ished flow of urine. If the constriction were carried so far that the 

 circulation of the kidney was entirely stopped, the flow of urine instantly 

 ceased. So far these results are those one would expect on the filtration 

 hypothesis. It is found, however, that the flow of urine is not restored 

 at once on relieving the constriction, and that after a few minutes' total 

 cessation of the renal circulation, more than an hour may elapse between 

 the restoration of the circulation and the recommencement of the secre- 

 tion. We have seen that in the case of lymph formation, where a 

 process of filtration almost certainly comes into play, a temporary 

 ischsernia increases the permeability of the vessel wall, so that, on the 



1 See especially Eckhard, Beitr. z. Anat. u. Physiol. (Eclchard), Giessen, 1869, Bd. iv. 

 S. 132, and 153-193. 



2 Loc. cit. 3 Loc. cit. 



