THE KIDNEYS AND URINE. 373 



wall of the bladder, as expose to view its hinder wall together with the 

 orifices of the ureters. The urine does not enter the bladder at any reg- 

 ular rate, nor is there a synchronism in its movement through the two 

 ureters. During fasting, two or three drops enter the bladder every 

 minute, each drop as it enters first raising up the little papilla on which, 

 in these cases, the ureter opens, and then passing slowly through its orifice, 

 which at once again closes like a sphincter. In the recumbent posture, 

 the urine collects for a little time in the ureters, then flows gently, and, 

 if the body be raised, runs from them in a stream till they are empty. 

 Its flow is increased in deep inspiration, or straining, and in active exer- 

 cise, and in fifteen or twenty minutes after a meal (Erichsen). The 

 urine collecting is prevented from regurgitation into the ureters by the 

 mode in which these pass through the walls of the bladder, namely, by 

 their lying for between half and three-quarters of an inch between the 

 muscular and mucous coats before they turn rather abruptly forward, 

 and open through the latter into the interior of the bladder. 



Micturition. The contraction of the muscular walls of the bladder 

 may by itself expel the urine with little or no help from other muscles, 

 when the sphincter of the organ is relaxed. In so far, however, as it is a 

 voluntary act, micturition is performed by means of the abdominal and 

 other expiratory muscles which, in their contraction, press on the abdom- 

 inal viscera, the diaphragm being fixed, and cause the expulsion, of the 

 contents of the bladder. The muscular coat of the bladder co-operates, 

 in micturition, by reflex involuntary action, with the abdominal muscles; 

 and the act is completed by the accelerator urince, which, as its name 

 implies, quickens the stream, and expels the last drops of urine from the 

 urethra. The act, so far as it is not directed by volition, is under the 

 control of a nervous centre in the lumbar spinal cord, through which, as 

 in the case of the .similar centre for defaecation (p. 288), the various 

 muscles concerned are harmonized in their action. It is well known that 

 the act may be reflexly induced, e.g., in children who suffer from intes- 

 tinal worms, or other such irritation. Generally the afferent impulse 

 which calls into action the desire to micturate is excited by over disten- 

 tion of the bladder, or even by a few drops of urine passing into the 

 urethra. 



END OF VOL. I. 



