412 THE NERVOUS SYSTEM. 



In man, when the sensibility of the bladder is exaggerated by inflam- 

 mation, the reflex impulse to micturition is increased, in intensity, pro- 

 ducing an intolerance of urine. Under these circumstances the urine 

 is discharged by a reflex act as soon as it has accumulated, in small 

 quantity, in the bladder. The impression which excites this discharge 

 is accompanied by sensation, but is too urgent to be resisted by the 

 will. 



On the other hand, injury of the spinal cord in the dorsal region 

 may cut off all sensibility and voluntary power over the bladder, and 

 yet the organ may be evacuated at regular intervals by the reflex action 

 of the lumbar portion of the cord. But diseases or injuries which 

 affect the cord in its lower portion, often produce complete paralysis; 

 of the bladder. The patient is consequently unable to discharge his. 

 urine in the ordinary way, and must be relieved by the introduction 

 of a catheter. If this be not done, the urine accumulates; being 

 retained for a time by the elastic tissues surrounding the neck of 

 the bladder and urethra. But after distention has reached a certain 

 point, this resistance is overcome ; and the urine dribbles away from 

 the urethra as fast as it is excreted by the kidneys. Paralysis of the 

 bladder, accordingly, first causes distention of the organ, afterward 

 followed by a continuous, passive, and incomplete discharge of its 

 contents. 



The spinal cord, in its character as a nervous centre, exerts a general 

 protective influence over the body. It presides over the involuntary 

 movements of the limbs and trunk; it supplies the requisite nervous 

 connections for the attitude and locomotion ; and by its control over 

 the rectum and bladder, it regulates the accumulation and discharge; 

 of the excrementitious products of the system. 



