Chap, hi.] ELIMINATION OF WASTE PRODUCTS. 543 



cases to act as a powerful diuretic, and in these cases either it 

 must act directly on the tubular epithelium or its effects in 

 constricting - the renal arteries must be less than its effects on 

 other small arteries or must pass off before the influence of the 

 heightened blood-pressure has disappeared. 



§ 343. Quite removed from the intervention of chemical 

 substances in the blood and yet most striking is the influence 

 on the kidney of the central nervous system. The potent 

 influence of emotions in promoting the secretion of urine is 

 proverbial, and the general features of 'nervous' urine, the water 

 increased out of proportion to the solid constituents, especially 

 seen in the " urina hysterica," which is hardly more than simple 

 water, often discharged in enormous quantity, at once suggests 

 the view that impulses originating in the brain and passing 

 down to the kidney along the vaso-dilator fibres, of whose exist- 

 ence evidence was given in § 333, lead to dilated blood vessels 

 and great play of glomerular activity, without perhaps produc- 

 ing any other direct effect on the economy ; though possibly the 

 same emotions by constricting the cutaneous and, it may be, 

 other vessels may raise the general blood-pressure and so help 

 the dilated renal vessels. 



