CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 549 



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 fre- 

 quently met with which seems to be of a different nature. The 

 bladder becoming full, but, owing to a failure in the mechanism 

 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 suf- 

 ficient 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. 



349. Whether, under normal conditions, the urine under- 

 goes 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 abra- 

 sion 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 ordi- 

 nary 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 con- 

 siderable 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. 



