CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 717 



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, 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 spinal centre 

 unable to act. 



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

 easily excited and frequently repeated reflex micturition. In 

 cases of cerebral or spinal disease a form of incontinence is 

 frequently met with which seems to be of a different nature. 

 The bladder becoming full, but, owing to a failure in the mechan- 

 ism of voluntary or reflex micturition, being unable to empty 

 itself by a complete contraction, a continual dribbling of urine 

 takes place through the urethra, the fulness of the bladder being 

 sufficient to overcome the resistance at the neck of the urethra. 

 It is probable, however, that even in these cases the flow is 

 partly caused by obscure, unfelt, intrinsic contractions of the 

 bladder. 



431. Whether, under normal conditions, the urine undergoes 

 any notable change during its stay in the bladder has been much 

 debated. Experiments shew that poisonous substances injected 

 into the bladder with all due care to avoid any abrasion of the 

 epithelium are absorbed and produce their usual effects. It has 

 also been stated that if a solution of urea be injected into the 

 bladder after ligature of both ureters, and allowed to stay for 

 some hours, part of the urea disappears. But at present there is 

 no very decided proof that under ordinary conditions either the 

 water or other constituents of urine are to any appreciable extent 

 absorbed by the bladder. 



Under abnormal conditions, as in inflammation or irritation of 

 the bladder, the urine may have undergone marked changes during 

 its stay in the bladder, one of the most common being a change of 

 some of the urea into ammonium carbonate, by which the urine 

 becomes alkaline. Under abnormal conditions also, the mucus of 



