716 MICTURITION. [BOOK n. 



the act imdergoes 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 urinaB, and at the same time 

 to suspend the tone of the sphincter vesicas externus. Clinical 

 experience also goes to shew the existence of a similar micturition 

 centre in man. 



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

 animals, experimental 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 inade- 

 quate 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 con- 

 tractions thus brought about in a reflex manner acquire strength 

 adequate to empty the bladder. 



Observations of vesical pressure may be most conveniently carried 

 out by introducing into the bladder a catheter connected with a water 

 manometer and a registering apparatus, and so arranged as to allow 

 fluid to be driven into or received from the bladder at pleasure. 



430. Involuntary micturition obviously of a reflex nature 

 has frequently 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 sometimes occurs in the adult as the 

 result of emotions, or at least sensory impressions, appears to be 

 the result of reflex action. In these several cases we may fairly 

 suppose that the centre in the spinal cord is affected by afferent 

 impulses reaching it along various sensory nerves or descending 

 from the brain. Hence we are led to the conception that when 

 we make water by a conscious effort of the will, what occurs is not 

 a direct action of the will on the muscular walls of the bladder, 

 but that impulses started by the will descend from the brain 

 after the fashion of afferent impulses and thus in a reflex manner 

 throw into action the micturition centre in the spinal cord. We 

 may draw an analogy between the micturition apparatus and 

 the respiratory mechanism. We saw reasons in the latter case 



