344 MUSCULAR MECHANISMS OF URINARY TRACT. 



contraction which is unable to overcome the resistance of the sphincter 

 and to give rise to micturition. The bilateral character of the con- 

 traction is due to the fact that certain of the fibres cross in the inferior 

 mesenteric ganglion, so that the lumbar nerves of one side send fibres 

 to both sides of the bladder. Stimulation of one hypogastric nerve 

 may produce a contraction which is more or less unilateral. Stimula- 

 tion of the sacral nerve-roots or of the nervi erigentes gives rise to a 

 strong contraction of the bladder, which is unilateral if the nerves of 

 only one side be stimulated, and which generally causes an expulsion 

 of urine, i.e. an active micturition. Stimulation of the branches of 

 the hypogastric plexus causes contraction of the bladder wall, limited to 

 the area of distribution of the excited filaments (Griffiths). 



Under some circumstances, it seems that stimulation of the upper 

 set of nerve fibres may cause a relaxation of the bladder, 1 or may 

 hasten the process of relaxation, after a contraction has been excited 

 by stimulation of the pelvic nerves. According to von Zeissl, 2 the 

 hypogastric nerves are the physiological antagonists of the sacral 

 nerves. If fluid be forced into the bladder by means of a cannula in 

 one ureter, at such a pressure that it is just able to overcome the 

 resistance of the sphincter and trickle through the urethra, stimulation 

 of the hypogastric nerves will at once stop the flow by reinforcing the 

 contraction of the sphincter. On the other hand, if the fundus of the 

 bladder be opened and tied round a glass tube connected with a 

 pressure-bottle, and the latter be so arranged that the fluid is just 

 unable to overcome the resistance of the sphincter, then stimulation of 

 the nervi erigentes will cause a relaxation of the sphincter, and a flow 

 of fluid through the urethra. In this case, the fundus being opened, 

 any contraction of the muscular wall of the bladder is ineffectual to 

 raise the pressure in the bladder, so that the result can only be 

 ascribed to the relaxation of the sphincter. The accumulation of urine 

 in the bladder would therefore be effected through the intermediation 

 of the upper set of fibres, while the evacuation would be brought about 

 by stimulation of the sacral fibres. Langley objects to these experiments, 

 that the results obtained by von Zeissl on stimulating the hypogastric 

 nerve might be due to a longitudinal contraction of the basal 

 portion of the bladder drawing the urethra forwards, whereas a 

 strong contraction, such as that produced by stimulating the nervus 

 erigens, even if it involved the urethra, would tend to widen the 

 urethral orifice, and so give the apparent effect of relaxation of 

 the sphincter. I am of opinion that von Zeissl's results are due 

 to a fallacious method of experiment. I have been unable to con- 

 firm him as to the inhibitory influence of the pelvic nerve on the 

 " sphincter vesicae." If his experiments be repeated, it will be found 

 that even when the fundus is connected by a fairly wide tube with a 

 reservoir, the sudden contraction of the bladder wall, on stimulation of 

 the pelvic nerve, causes a considerable rise of pressure in the bladder. 

 The expulsion of urine is caused by this rise of pressure, and not by any 

 relaxation of the sphincter. If a tube one inch in diameter be tied i 

 into the fundus, and fluid poured into the tube until it just drops from 

 the urethra, stimulation of the pelvic nerve does not alter the rate of 



1 Griffiths, Joum. Anat. and Physiol., London, 1894, vol. xxv. p. 540 ; and 1895, 

 vol. xxvi. pp. 60 and 225. 



2 Arch./, d. ges. Physiol., Bonn, 1893, Bd. liii. S. 560. 



