CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 685 



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 the urine, which in a healthy man is insignificant, 

 though in some animals, for instance the horse, it occurs in 

 considerable quantity, is largely increased during the stay in the 

 bladder. Since there are in man no goblet cells in the vesical 

 epithelium (in the frog they are present) or mucus glands in the 

 walls of the bladder, this mucus must be supplied by an abnormal 

 metabolism of the ordinary epithelial cells. 



