vni THE EXCEETION OF UKINE 465 



electrical, or thermal stimulation of the bladder walls, after which 

 the pressure necessary to produce incontinence was again deter- 

 mined. They found that increase of tone in the detrusor was always 

 under these conditions associated with increase of tone in the 

 sphincter, so that more pressure was necessary to force the urine 

 through it. 



The involuntary micturition of fright, formerly interpreted 

 as the effect of a sudden paralysis of the sphincters, may result 

 from an analogous process. Mosso and Pellacani noted in support 

 of this view that when a dog is frightened by shouts, or sudden 

 pain, there is an increase of tone in the sphincters, expressed in 

 the fact that a much higher pressure than the normal is required 

 to force fluid through the urethra. This result can, however, be 

 explained by a reflex contraction of the sphincter, due to the 

 injection through the urethra ; it does not seem to us to prove the 

 contention of the authors. 



In the adult also, owing to the preponderance of the detrusor 

 activity over that of the internal sphincter, involuntary micturi- 

 tion would take place each time that excessive accumulation of 

 urine, or increased activity of the nerves to the bladder, raised 

 the vesical tension beyond a certain point, if the sphincter were 

 not (in order to retain the urine within the bladder for a certain 

 time longer) reinforced by the active voluntary intervention 

 of Wilson's muscle, and of the compressor urethrae, as well as of 

 the musculi bulbo-cavernosi, to which is associated the action of 

 the sphincter ani. When these coadjuvants are inadequate, in- 

 voluntary micturition takes place, as not infrequently occurs in 

 young children. 



The mechanism of the micturition which is aroused by con- 

 sciousness of distension in the bladder and irritation in the region 

 of the vesical orifice, leading to an imperative desire for relief, is 

 more complex. The origin of these sensations must first be 

 examined. 



They are certainly not due directly to the tension of the 

 bladder, because the amount of urine passed under different con- 

 ditions is very variable, and is not in ratio with the strength of 

 the desire. There may often be an urgent need to micturate, 

 when very little urine is present in the bladder. This leads 

 to the conclusion that the tone of the bladder wall is very vari- 

 able, and that the need to micturate depends less on the passive 

 distension of the bladder than on its active reaction to the contents, 

 i.e. the pressure of the urine within the bladder. 



In this connection the researches of Mosso and Pellacani on 

 the great reflex excitability and variable tone of the muscular 

 coat of the bladder are interesting. It is susceptible to mental 

 influences, whether these are accompanied by changes in arterial 

 pressure or not. At constant pressure the bladder may contain 



VOL. II 2 H 



