NERVOUS MECHANISM OF MICTURITION. 415 



stimulate them and cause the sphincter to remain tonically con- 

 tracted, and passing from the mucous membrane of the urinary 

 passages to these gangliouic cells in the cord are two sets ; one 

 of which excites the contractions of the detrusor urinse and the 

 other inhibits the tonic action of the retaining centre. 



The action of the ganglionic cells that stimulate the sphincter 

 muscle, can, to a certain extent, be either aided or checked by 

 means of cerebral influences, so that two kinds of fibres a 

 stimulating and an inhibitory one must pass from the hemi- 

 spheres to the micturating centre in the cord. 



Those cells which govern the motions of the detrusor seem to 

 be least under voluntary control, and are probably only stimu- 

 lated to action under normal circumstances by the impulses 

 arising from the urinary passages, and hence are simply reflex 

 centres. 



The effect of certain emotions on the act of micturition seems 

 to show that those ganglion cells in the cord which cause the 

 bladder to contract are connected with the higher centres. Thus, 

 extreme terror (in a dog, at least) often causes a forcible expul- 

 sion of urine, and great anxiety or impatience seems in man 

 often to have a checking influence, causing great delay in initia- 

 ting micturition. 



