EVACUATION OF THE URIXE. 521 



The urinary bladder, especially when considerably distended, exhibits the 

 occurrence of intermittent slight contractions, which can be compared with the 

 peristaltic movements of the intestines. Even the excised frog's bladder, and even 

 portions thereof without ganglia, exhibit similar rhythmic contractions, which 

 can be increased by heat. After division of all of the nerves of the bladder, 

 bleeding with asphyxia is still followed by contractions as a result of direct stimu- 

 lation of the muscles of the bladder. The contractions occur, further, more 

 actively in the presence of derangement of the circulation in the bladder, or of 

 venosity of the blood, in the same way as the movements of the intestine are 

 brought about in marked degree by like influences. In this category belongs the 

 evacuation of the urine when the action of the heart ceases in cases of sudden 

 asphyxia or protracted suppression of respiration. As emotional disturbances 

 also influence the contraction of the walls of the bladder, the evacuation of the 

 urine in connection with sudden fear can be explained in this manner. In the 

 state of apnea, as well as in apneic intervals after persistent deep respiratory 

 movements, the independent contractions of the bladder cease. 



In order to comprehend the mechanism of the retention of the urine 

 in the bladder, as well as of its evacuation, a description is necessary of 

 the following nervous apparatus which participates in these processes : 



T . The sensory nerves of the walls of the bladder are derived from the 

 first, second, third, and fourth posterior sacral roots. A number of 

 sensory fibers pass into the spinal cord through the intermediation of the 

 hypogastric plexus. The sensory nerves pass upward in the cord to the 

 cerebral cortex. 



2. The center for reflex stimulation of the unstriated musculature of 

 the wall of the bladder vesicospinal center is situated in the neigh- 

 borhood of the fourth lumbar vertebra, in the dog. 



3 . The motor tracts pass from this center to the unstriated muscula- 

 ture of the wall of the bladder through the nerves between the second 

 lumbar by way of communicating branches of the sympathetic 

 and the fourth sacral by way of the nervi erigentes. Irritation of the 

 sensory nerves of the wall of the bladder causes reflex contraction of the 

 bladder-wall. 



In addition to the sensory nerves of the bladder, the reflex described 

 may be excited also by irritation of other sensory nerves; thus, active 

 tickling, or warming of the region of the knee during sleep at times causes 

 evacuation of urine, likewise the hearing of splashing and whistling 

 sounds. In animals, stimulation of certain sensory nerves likewise 

 causes contractions of the bladder. 



Omitting consideration of the sphincter muscle of the urethra, the 

 sensation of a distended bladder will become apparent as soon as the 

 bladder is moderately distended. Then the mechanical irritation of the 

 sensory nerves of the bladder in the mucous membrane excites in* the 

 vesicospinal center the reflex through the motor nerves of the unstriated 

 musculature of the bladder, and in consequence of this the walls of the 

 bladder undergo contraction . This constitutes the process as it takes place , 

 for instance, normally always in infants, who do not as yet have control 

 of the urethral sphincter. Also voluntary evacuation of the bladder, 

 whatever the degree of distention, is always effected only through exci- 

 tation of the reflex described. The will is incapable of influencing di- 

 rectly the unstriated musculature of the bladder ; and this is emphasized 

 particularly by the author, in opposition to the statements of many other 

 observers. To induce reflex stimulation of this movement of the bladder, 

 principally in the presence of considerable degrees of distention, the 

 direction of the attention to the sensations in the urinary apparatus 



