644 THE SECRETION OF URINE. 



The course taken by the nerves is very variable. The nerves are derived 

 from the sympathetic chain. From the ganglia lying on the head of the 

 thirteenth rib, or from the cord immediately below this, is given off a 

 large nerve (larger than the continuation of the sympathetic chain), 

 which perforates the crus of the diaphragm, and is called the large 

 splanchnic nerve. Between this ganglion and the next two or three 

 ganglia below, are given off' three or four smaller filaments, known as the 

 small splanchnic nerves. (It must be noted that this terminology is not 

 comparable with that employed in human anatomy, where the term 

 splanchnics is confined to the nerves given off by the sympathetic chain 

 while in the thoracic cavity.) These large and small splanchnics form a 

 plexus situated behind the suprarenals, and from which filaments are 

 given off to the coeliac and superior mesenteric ganglia and solar plexus. 

 From the plexus behind the suprarenals arise a number of filaments, 

 which form a meshwork in the fat and connective tissues between the 

 suprarenal and kidney, and then pass to the kidney around, and closely 

 applied to, the renal artery. 



According to v. Wittich, 1 the renal nerves in the rabbit, dog, and man 

 consist of two parts ; one part of them forms a plexus closely investing 

 the renal artery, while the other consists of several filaments which enter 

 the kidney parallel to the vessels, and can be traced along these as far 

 as the cortex. 



The termination of these nerves in the kidney has been recently inves- 

 tigated by Berkeley, 2 using Golgi's method. He finds that from the vascular 

 nerves fine filaments arise to be distributed throughout the cortical and 

 medullary regions in the form of a vast open network. The glomeruli are 

 surrounded by a wide-meshed plexus of fibres, having terminal end knobs, 

 approximated closely to Bowman's capsule, but not penetrating that membrane, 

 nor passing to the glomerular capillaries. Fibres also pass off from the vascular 

 plexus to be distributed upon the convoluted tubes, with terminations which 

 penetrate the membrana propria of the tube, presumably to enter the cement 

 substance between the epithelial cells. Berkeley looks upon these latter nerves 

 as probably secretory in function. 



With regard to the connection of the renal nerves with the central 

 nervous system, Bradford 3 has shown that, so far as the efferent nerves 

 to the renal vessels are concerned, these leave the spinal cord through 

 the anterior roots. Most of the fibres are contained in the eleventh, 

 twelfth, and thirteenth dorsal nerve roots. 



Influence of blood flow on secretion of urine. We are now in a 

 position to consider the influence exerted by changes in the circulation 

 through the kidney on the secretion of urine. It must be remembered 

 that a rise of general blood pressure does not necessarily carry with it an 

 increased pressure in the glomerular capillaries or an increased blood flow 

 through the kidney. Thus, under many conditions, a rise of general 

 blood pressure is brought about by a constriction of all the visceral 

 arteries, including those of the kidney, and such constriction is more 

 than sufficient to counteract the effects of the increased blood pressure. 

 If we take a tracing of the kidney volume, for instance, in asphyxia, we 



1 Konigsberger, Med. Jahrl., Wien, 1860, Bd. iii. S. 52 (quoted from Heideuliain in 

 Hermann's "Handbuch"). 



2 Journ. Path, and BacterioL, Edin. and London, 1893, vol. i. p. 406. 



3 Journ. PhysioL, Cambridge and London, 1889, vol. x. p. 358. 



