1296 PHYSIOLOGY 



sphincter could be overcome without any alteration of its state of con- 

 traction, i.e. the point at which fluid injected into the bladder through 

 the ureter began to escape from the urethra without stimulation of 

 any nerves whatever. 



Observations on man would support the view that an active 

 relaxation of the sphincter trigoni is a necessary part of the act of 

 micturition. Thus in experiments by Reyfisch a rigid catheter was 

 introduced into the bladder, which was fully distended with fluid. 

 On withdrawing the catheter until its opening lay just outside the 

 bladder in the posterior urethra, the flow of urine stopped. The 

 man, however, was able to micturate directly he was told to, and to 

 stop again at will. It was impossible in this case for any of the 



Exc. 



FIG. 539. Curve showing rise of pressure in the bladder caused by stimulation 



of s, sacral nerves ; h, hypogastric nerves. (FAGGE.) 



The scale indicates centimetres of water. 



urethral muscles to be concerned, since the rigid catheter impeded 

 their action. The relaxation of the sphincter must therefore be 

 brought about by impulses descending the pelvic visceral nerves, 

 which we may regard as motor to the ' detrusor ' and inhibitory to the 

 sphincter of the bladder. 



Section of the nerve on one side causes no abnormality in mic- 

 turition. After three weeks, stimulation of the intact nerve causes 

 contraction of the whole bladder, owing to the outgrowth of pre- 

 ganglionic fibres from the sound trunk to the decentralised ganglia of 

 the opposite side (Elliott). Section of both nerves paralyses micturi- 

 tion, but power of partial evacuation of the bladder may return in a 

 few weeks. If now the hypogastrics be cut, or even the sacral cord 

 extirpated, the bladder is not completely paralysed, but its evacua- 

 tion becomes unconscious and incomplete. 



ACTION OF THE HYPOGASTRIC NERVES. These nerves, which 

 are derived from the sympathetic system, show marked differences 



