CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 677 



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. 



423. Quite removed from the intervention of chemical sub- 

 stances 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 existence evidence was given in 413, 

 lead to dilated blood vessels and great play of glomerular activity, 

 without perhaps producing 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. In the case of the urine of 

 hysteria we are tempted, more perhaps than in any other instance, 

 to accept the hint previously thrown out that it is possible for the 

 vasa afferentia of the glomeruli to be alone dilated, so that the 

 greater part of the renal blood is directed to the glomeruli and 

 the epithelium of the tubules left in its usual quiet. But this 

 is as yet pure speculation. 



