THE DISCHARGE OF URINE. 429 



There are facts, however, which prevent the acceptance of so simple a 

 view. In the first place, in cases of urethral obstruction, where the bladder 

 cannot be emptied when it reaches its accustomed fulness, the increasing 

 distention sets up fruitless but powerful contractions of the vesical walls, 

 contractions which are clearly involuntary in nature, which wane or disap- 

 pear, and return again and again in a rhythmic manner, and which may be 

 so strong and powerful as to cause great suffering. It seems that the fibres 

 of the bladder, like all other muscular fibres, have their contractions aug- 

 mented in proportion as they are subjected to tension. Just as a previously 

 quiescent ventricle of a frog's heart may be excited to a rhythmic beat by 

 distending its cavity with blood, so the quiescent bladder may, quite inde- 

 pendently of the will, be excited, by the distention of its cavity, to a peristaltic 

 action which in normal cases is never carried beyond a first effort, since with 

 that the bladder is emptied and the stimulus is removed, but which in cases 

 of obstruction is enabled clearly to manifest its rhythmic nature. 



In the second place it has been shown that quite normal micturition may 

 take place in a dog in which the lumbar region of the spinal cord has been 

 completely and permanently separated by section from the upper dorsal 

 region. In such a case there can be no exercise of volition, and the whole 

 process appears as a, reflex action. When under these circumstances the 

 bladder becomes full (and otherwise apparently the act fails) any slight 

 stimulus, such as sponging the anus or slight pressure on the abdominal 

 walls, causes a complete act of micturition ; the bladder is entirely emptied, 

 and the stream of urine toward the end of the act undergoes rhythmical 

 augmentations due to contractions of the ejaculator urinse. These facts can 

 only be interpreted on the view that there exists in the lower spinal cord (of 

 the dog) what we may speak of as a micturition centre capable of being 

 thrown into action by appropriate afferent impulses, the action of the centre 

 being such as to cause a contraction of the walls of the bladder and of the 

 ejaculator urinse, and at the same time to suspend the tone of the sphincter 

 vesicle externus. Clinical experience also goes to show the existence of a 

 similar micturition centre in man, placed higher up in the cord than the 

 corresponding " genital " centre governing the genital organs. 



Moreover, we have, in the case both of man and of other animals, experi- 

 mental and other evidence that contraction of the bladder is frequently 

 brought about by reflex action. Thus the pressure within the bladder when 

 observed for any length of time is found to be subject to considerable and 

 manifold variations. Over and above passive changes in pressure due to the 

 respiratory movements, through which the bladder is pressed upon at each 

 descent of the diaphragm, active contractions, of a strength inadequate to 

 bring about micturition, are from time to time observed. These in some 

 instances appear to be spontaneous, or to be the result of emotions, but they 

 may be readily induced in a reflex manner by stimulating various sentient 

 surfaces or sensory nerves. And common experience affords many instances 

 where vesical contractions thus brought about in a reflex manner acquire 

 strength adequate to empty the bladder. 



Observation of vesical pressure may be most conveniently carried out by intro- 

 ducing into the bladder a catheter connected with a water manometer and a regis- 

 tering apparatus, and so arranged as to allow fluid to be driven into or received 

 from the bladder at pleasure. 



364. Involuntary micturition obviously of reflex nature has fre- 

 quently been observed in cases of paralysis from disease of or injury to the 

 spinal cord ; and the involuntary micturition which is common in children, 

 as the result of irritation of the penis and genital organs, and which some- 



