184: EXCRETION. 



phragm, the resistance of the sphincter is overcome, and a 

 jet of urine flows with considerable force from the urethra. 

 All voluntary action may then cease for a time, and the 

 bladder will nearly empty itself; but the force of the jet 

 may at any time be considerably increased by voluntary 

 effort. 



It is a question whether the bladder be capable of entirely 

 emptying itself by the action of its muscular walls. That 

 almost all the urine may be expelled in this way in the 

 human subject there can be no doubt ; and it has been shown 

 by experiments upon some of the inferior animals that the 

 bladder may be completely evacuated when it has been 

 removed from the abdominal cavity. This fact was observed 

 long ago by Magendie in dogs. 1 In vivisections we have 

 frequently observed the bladder so firmly contracted that it 

 could contain hardly more than a few drops of liquid. 



Toward the end of the expulsive act, when the quantity 

 of liquid remaining in the bladder is slight, the diaphragm 

 and the abdominal muscles are again called into action, and 

 there is a convulsive, interrupted discharge of the small 

 quantity of urine that remains. At this time the impulse 

 from the bladder, and, indeed, the influence of the abdomi- 

 nal muscles and diaphragm, are very slight, and the flow of 

 urine along the urethra is aided by the contractions of its 

 muscular walls and the action of some of the perineal mus- 

 cles, the most efficient being the accelerator urinse ; but with 

 all this muscular action, a few drops of urine generally re- 

 main in the male urethra after the act of urination is accom- 

 plished. The process of evacuation of urine in the female is 

 essentially the same as in the male, with the exception of the 

 slight modifications due to differences in the direction and 

 length of the urethra. 



The movements of the bladder are regulated by the ner- 

 vous system. According to the researches of Budge, the 

 influence of the nervous system operates through the sympa- 



1 MAGENDIE, Precis elementaire de physiologic, Paris, 1836, tome ii., p. 485. 



