viii THE EXCRETION OF UEINE 463 



sphincter of striated fibres, which is thrown into activity by 

 voluntary impulses only when it is necessary to delay evacuation 

 of the bladder, on feeling a desire to pass urine. 



We must accordingly conclude that the urethral orifice of the 

 bladder is provided with an internal sphincter of plain muscle 

 (morphologically distinct from the circular layer of the bladder), 

 on the tonic contraction of which depends the retention, on its 

 paralysis the incontinence of urine. 



While it is difficult to give experimental proof, we regard it as 

 probable that the tone of the internal sphincter of the bladder is 

 not constant, but varies with the tension of the bladder, and that 

 it is not automatic but reflex in character, i.e. determined by the 

 presence of the urine and the pressure which the latter exerts 

 upon the urethral orifice. The same opinion was clearly set forth 

 by Haller (1778) in the following words: "Videtur urinae 

 modicam copiam in convexo vesicae fundo versus rectum 

 intestinum, sub urethra producto, facile et absque sensu colligi ; 

 deinde sphincterem incipere stringi, quando major nunc lotii copia 

 ad urethrae ostium adscendit, et eo majorem ejus ruusculi laborem 

 esse, quo altior super urethram nunc urinae columna est, suo 

 pondere urethrae ostium nitentis." 



Experimental evidence for the theory of the retention of urine 

 by the tone of the internal sphincter of plain muscle has recently 

 been given by Eehfisch in I. Munk's laboratory (1897). In five 

 dogs which for over three months survived the severe operation of 

 removal of the prostate, including Wilson's muscle (external 

 striated sphincter), he saw that the urine was perfectly retained in 

 the bladder without a trace of incontinence. The same fact was 

 demonstrated on man by a very elegant experiment. By means of 

 a rigid catheter, he injected into the bladder of a man as much 

 boric acid solution as was required to fill it completely. On then 

 drawing the catheter back as far as the prostatic portion of the 

 urethra, so as to inhibit the contraction both of Wilson's muscle 

 which surrounds it, and of the compressor urethrae which surrounds 

 the membranous part of the urethra, he observed that the subject 

 was able not only to pass urine at will, but also to interrupt the 

 evacuation at any moment, by relaxation or contraction of the 

 internal sphincter (the only one he could control), so as to open or 

 close the urethral orifice. 



Again : by other experiments on dogs Kehfisch was able to 

 show that, under ordinary conditions of closure of the urinary 

 canal, the external sphincter and the compressor urethrae play 

 only a subordinate part, the retention of the urine being specifically 

 the task of the internal sphincter. After opening the peritoneal 

 cavity and exposing the bladder, he connected one of the ureters 

 with a manometer by a cannula which penetrated into the bladder, 

 and introduced into the other ureter the cannula of a syringe by 



