CHAP, iv.] RENAL SECRETION. 413 



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

 of the ejaculator urinse, and possibly at the same time to suspend 

 the tone of the sphincter vesicse. 



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 respi- 

 ratory movements, when the bladder is pressed upon at each 

 descent of the diaphragm, active contractions, of a strength in- 

 adequate to bring about micturition, are from time to time 

 observed. These in some instances appear to be spontaneous, or 

 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 either with an 

 oncograph, or some other similar registering apparatus, so arranged as to 

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



Involuntary micturition obviously of reflex nature has frequently 

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

 spinal cord ; and the involuntary micturition which is common in 

 children, as the result of irritation of the pelvis 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 lumbar 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 lumbar spinal cord. 

 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, 

 the failure in micturition under these circumstances may be 

 explained by supposing that the shock of the spinal injury or 

 some extension of the disease has rendered the lumbar centre 

 unable to act. 



The so-called incontinence of urine in children is simply an 



