468 THE SPINAL CORD. 



is compelled to allow it to take place at once. The discharges are then 

 said to be ''involuntary." 



If the cord, on the other hand, be injured or divided in its middle or 

 upper portions, the sensibility and voluntary action of the sphincter are 

 lost, because its connection with the brain has been destroyed. The 

 evacuation then takes place at once, by the ordinary mechanism, as soon 

 as the rectum is filled, but without any knowledge on the part of the 

 patient. The discharges are then said to be " involuntary and uncon- 

 scious." 



Finally, if the lower portion of the cord, in the living animal, be broken 

 up by means of an instrument introduced into the spinal canal, the tonic 

 contraction of the sphincter ani at once disappears. The same effect is 

 produced, in man, by disorganization of the lower part of the spinal 

 cord from injury or disease. The sphincter ani is then permanently 

 relaxed, and the feces are evacuated almost continuously, without the 

 knowledge or control of the patient, as fast as they descend into the 

 rectum from the upper portions of the intestinal canal. 



The urinary bladder is also an organ both of reservoir and evacua- 

 tion, which is protected by the circular bundle of muscular fibres at the 

 commencement of the urethra, known as the " sphincter vesica?." While 

 the nerves distributed to the kidneys are derived exclusively from the 

 coeliac plexus of the sympathetic system, those of the bladder consist 

 partly of sympathetic filaments from the mesenteric ganglia, and partly 

 of cerebro-spinal filaments from the lumbar portion of the spinal cord, 

 both of these sets having united in the abdomen to form the hypogastric 

 plexus. 



The tonic contraction of the vesical sphincter during health, by which 

 the urine is retained in the bladder, is a continuous, involuntary, and 

 unconscious act, like that of the sphincter ani. When the time comes 

 for evacuation, the sphincter is relaxed by a voluntary impulse, and the 

 muscular coat of the bladder contracts so as to expel its contents; but 

 although the commencement of this process is a voluntary one, the sub- 

 sequent contraction of the muscular walls of the bladder continues with- 

 out any effort of the will. According to the experiments of Giannuzzi 1 

 on dogs, irritation of the lumbar portion of the spinal cord by pricking 

 with a steel needle, causes contraction of the urinary bladder ; and 

 these contractions are no longer produced after division of the roots of 

 the sacral nerves. Irritation of either the sympathetic or the spinal 

 nerve filaments going to the hypogastric plexus produced contraction 

 of the bladder, but these contractions were more energetic in the latter 

 case than in the former. 



Diseases or injuries of the spinal cord which cause complete para* 

 plegia, also usually produce a paralysis of the bladder. So far as re- 

 gards contraction of the bladder itself, therefore, this act is under the 

 influence both of the sympathetic and cerebro-spinal systems ; but its 



1 Journal dc la Physiologic. Paris, 1863, tome vi. p. 22. 



