SEC. 3. MICTURITION. 



The urine, like the bile, is secreted continuously ; the flow may 

 rise and fall, but, in health, never absolutely ceases for any length 

 of time. The cessation of renal activity, the so-called suppression 

 of urine, entails speedy death. The minute streams passing con- 

 tinuously, now more rapidly now more slowly, along the collecting 

 and discharging tubules, are gathered into the renal pelvis, whence 

 the fluid is carried along the ureters partly by pressure and gravity 

 and partly by the peristaltic contractions of the muscular walls 

 of those channels (see p. 101) into the urinary bladder. When a 

 ureter is divided in an animal, and a cannula inserted, the urine 

 may be observed to flow from the cannula drop by drop, slowly or 

 rapidly according to the rate of secretion. Frequently, after a 

 series of single drops at long intervals, several drops follow in 

 rapid succession, apparently urged by a peristaltic wave. In the 

 urinary bladder, the urine is collected, its return into the ureters 

 being prevented by the oblique entrance into the bladder and 

 valvular nature of the orifices of those tubes ; and its discharge from 

 thence in considerable quantity is effected from time to time by 

 a somewhat complex muscular mechanism, of the nature and 

 working of which the following is a brief account. 



The involuntary muscular fibres forming the greater part of the 

 vesical walls are arranged partly in a more or less longitudinal 

 direction forming the so-called detrusor urinse, and partly in a 

 circular manner, the circular fibres being most developed round 

 the neck of the bladder and forming there the so-called sphincter 



