684 MICTURITION. [BOOK n. 



Over and above passive changes in pressure due to the respi- 

 ratory 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. 



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 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 to 

 think that when the will interfered with the respiratory move- 

 ments, it did so by acting upon the nervous mechanism in the 

 central nervous system and not by acting directly on the muscular 

 fibres of the diaphragm and other respiratory muscles. And the 

 case of the plain muscular fibres of the bladder seems even stronger 

 than that of respiratory muscles so largely skeletal in nature. 

 We might also draw an analogy with the heart. We are not able 

 to throw into action, by any direct effort of the will, the cardiac 

 augmentor mechanism. Were we able to do so powerfully and 

 suddenly, we might throw into violent action a weakly beating heart 

 much in the same way that we empty an obscurely contracting 

 bladder. ^Nor is this view negatived by the fact that paralysis of the 

 bladder, or rather inability to make water either voluntarily or in 

 a reflex manner, is a common symptom of cerebral or spinal disease 

 or injury. Putting aside the cases in which the reflex act is not 

 called forth because the appropriate stimulus has not been applied, 



