476 URO-GENITAL SYSTLJf. 



These co-ordinated contractions, which occasion micturition, 

 are made under the influence of the spinal cord, and particu- 

 larly its lumbar portion. Budge has sought to fix the precise 

 seat of this centre, and by experiments has placed the centre 

 of innervation of the bladder in the fourth lumbar vertebra 

 (in dogs and rabbits). Kupresson localizes this centre be- 

 tween the fifth and sixth lumbar vertebra. 



Sensibility of the prostatic mucous surface is very impor- 

 tant, since this is the point of origin for the essential reflex 

 action ; loss of this sensibility is the cause of that form of in- 

 continence of urine called enuresis, or nocturnal incontinence ; 

 this involuntary voiding of urine, as in similar cases of invol- 

 untary emission of feces, is explained by the lack of sensibility 

 of the mucous surfaces to the contact of excrementitial pro- 

 ducts, and in this particular case, the absence of a premon- 

 itory sensation of the desire to urinate. 



Some moments after the continued distention of the vesical 

 reservoir, it reacts anew, and the urine proceeds to the pros- 

 tatic portion of the urethra, where it stimulates anew the 

 same reflex action, and so on. This explains the intermittent 

 form of the desire for micturition. If these phenomena are 

 often repeated, the reflex contraction of the urethral sphincter 

 gradually loses its energy, and the urine tends to pass out 

 through the urethral canal; hence the distress occasioned by 

 resisting the desire to urinate. Thus it is seen that every 

 time a true active resistance is offered to the passage of urine, 

 this opposition is made, not by the sphincter of the bladder, 

 but by the sphincter of the urethra, the constrictor urethroe 

 muscle, which is the only one of these muscles which is 

 striated or voluntary. 1 



If a sound be introduced into the urethra, as soon as its tip 

 touches the mucous membrane of the prostatic portion, it will 

 occasion a sensation similar to the desire to urinate ; we refer 

 this sensation to the other extremity of the urethra, simply 

 because it is one of those associated sensations, examples of 

 which we have already cited. (See General Sensibility and 

 Sensations, pp. 79 and 388.) 



When we yield to the desire, in spite of the absence of 

 any obstacle on the part of the sphincter or constrictor 

 urethra, we cannot completely evacuate the contents of the 

 bladder by the simple contraction of its walls. We must 



1 See Carayon, " De la Miction dans ses Rapports avec la Phy- 

 siologic et la Pathologic." These de Strasbourg, 1865, No. 814. 



