DISCHARGE OF THE URINE. 183 



shown that this may be produced by galvanization of the 

 anterior root of the eleventh dorsal nerve. 1 Notwithstand- 

 ing these facts, it is difficult to estimate the amount of influ- 

 ence ordinarily exerted by peristaltic contractions of the 

 ureters ; but when there is excessive accumulation of urine 

 in the bladder, or when there is obstruction from any cause, 

 such as the presence of a renal calculus, these contractions 

 are probably quite energetic. 



When the urine has accumulated to a certain extent in 

 the bladder, a peculiar sensation is experienced which leads 

 to the act for its expulsion. This desire to discharge the 

 urine is probably due to the impression produced by the 

 distention of the bladder, and is conveyed to the nervous 

 centres through the sympathetic system. The intervals at 

 which it is experienced are exceedingly variable. The urine 

 is usually voided before retiring to rest and upon rising in 

 the morning, and generally two or three times, in addition, 

 during the day. It is dependent, however, very much upon 

 habit, upon the quantity of liquids ingested, and upon the 

 degree of activity of the skin ; the latter conditions modify- 

 ing the quantity of urine. 



Evacuation of the bladder is accomplished by the mus- 

 cular walls of the organ itself, aided by contractions of the 

 diaphragm and the abdominal muscles and certain muscles 

 which operate upon the urethra, and is accompanied by 

 relaxation of the sphincter vesicae. This act is at first 

 voluntary, but once commenced, it may be continued by 

 the involuntary contraction of the bladder alone. During 

 the first part of the process, the distended bladder is com- 

 pressed by the voluntary contraction of the diaphragm and 

 the abdominal muscles ; and this, after a time, excites the 

 action of the bladder itself. A certain period usually elapses 

 then before the urine begins to flow. When the bladder 

 contracts, aided by the muscles of tho abdomen and the dia- 



1 Unpublished lectures delivered by Bernard at the College of France in the 

 Summer of 1861. 



