462 



PHYSIOLOGY 



CHAP. 



body can support the pressure of a column of about 900 mm. of 

 water before it. empties. Heidenhain and Colberg tried to demon- 

 strate the tonic action of the sphincter vesicae by introducing a 

 sound into the ureter as far as the neck of the bladder, and 

 measuring the pressure necessary to overcome the resistance of the 

 sphincter and to permit the penetration of fluid into the bladder, 

 which pressure is reduced after the death of the animal. But 

 it may be objected that the external pressure which is required 



Fio. 127. A. Section through bladder of young woman near the posterior wall of the curve. (Versari.) 

 Si, internal sphincter ; the bundle of circular fibres as seen in cross-section, with longitudinal 

 fibres from the detrusor urinae showing between. Se, external sphincter of striated muscle ; 

 fl,, fc., longitudinal and circular fibres, of which the muscular coat of the bladder is composed, 

 and which unite in forming the detrusor urinae. B. Section through bladder of girl near the 

 posterior wall of the cervix. (Versari.) Lettering as in A. Here the external sphincter is 

 not visible. It is nearly always incomplete and ill-developed in females, and is probably 

 absent in infancy. 



in order to force the fluid into the bladder, sets up a reflex 

 which causes the sphincter to contract, or at least increases 

 its tonicity. The better demonstration of this normal tonic 

 activity seems to us to lie in the fact of the incontinence of urine 

 which is not uncommon in cases of disease of the brain or spinal 

 cord. 



Since even in sleep, when the action of all voluntary muscles 

 is relaxed, the urine is normally retained in the bladder, it is clear 

 that the tonic activity to which the retention is due depends on 

 the internal sphincter of plain muscle, and not on the external 



