4 io A MANUAL OF PHYSIOLOGY 



the nerve-roots, the splanchnics, or the renal nerves is shrinking of 

 the kidney, with diminution or cessation of the secretion of urine. 

 But slow rhythmical stimulation of the roots causes increase of 

 volume, the dilators being by this method excited in preference to 

 the constrictors. 



Section of the renal nerves is followed by relaxation of the 

 small arteries in the kidney, and consequent swelling of the 

 organ. The flow of urine is greatly increased, and some- 

 times albumin appears in it, the excessive pressure in the 

 capillaries (particularly in those of the glomeruli) being 

 supposed to favour the escape of substances to which the 

 renal epithelium refuses a passage under normal conditions. 



The recent investigations of Berkely have shown that the 

 renal nerves, entering at the hilum, branch repeatedly, so 

 as to form a wide-meshed plexus around the arteries, and 

 accompany them even to their finest ramifications in the 

 cortex. - No nerve-fibres have as yet been seen on the veins 

 in the kidney-substance or on the straight arteries. Coming 

 off from the nerves surrounding the arteries are fine fibres 

 which are distributed to the convoluted tubules, and are 

 perhaps secretory nerves. Some of them terminate in 

 globular ends, others in fine threads that pass through the 

 membrana propria. 



It is often assumed that the renal nerves affect chiefly 

 the afferent arterioles of the glomeruli ; but there seems to 

 be no experimental ground for this view, which is merely a 

 .doctrinaire deduction from Ludwig's filtration theory. For 

 if that theory, or any modification of it which postulates a 

 close connection between the blood-pressure in the glome- 

 rular capillaries and the rate of secretion of urine, be accepted, 

 it is evidently an advantage that there should be no similar 

 influence on the efferent arterioles, since constriction of 

 both would not necessarily cause any fall, nor dilatation of 

 both any rise, of intra-glomerular pressure. Heidenhain's 

 suggestion, that the velocity of the blood-flow, and not the 

 pressure in the glomeruli, is the determining factor in 

 urinary secretion, does not require any arbitrary restriction 

 of the tract influenced by the renal vaso-motor nerves. If 

 both afferent and efferent vessels were constricted, the blood- 



