NERVOUS MECHANISM OF URINARY SECRETION. 407 



of peptones, and that in the small intestine when delay in absorp- 

 tion occurs the decomposition of peptones results, because in pro- 

 longed pancreatic digestion these peptones are changed into leucin 

 (C 6 H 13 NO 2 ) and tyrosin (C 9 H n NO s ) and as such pass into the 

 portal circulation to be borne to the liver. In the liver it is 

 highly probable that these bodies are converted into urea, for, 

 when they are introduced into the intestinal tract, they are ab- 

 sorbed and an excess of urea appears in the urine. Thus the ex- 

 cessive part of the proteid food, before it really enters the system, 

 is broken up in the intestine into bodies which, notwithstanding 

 the chemical difficulty of explaining the process, may be regarded 

 as a step towards the formation of urea. 



NERVOUS MECHANISM OF THE URINARY SECRETION. 



With regard to the influence exerted by the nervous system on 

 the renal secretion, we have but little satisfactory information, 

 although there can be no doubt that here, as in other glands, the 

 process is under the control of the nerves. Many of the circum- 

 stances which cause greater activity of secretion, such as taking 

 large quantities of water, etc., have no effect on the general blood 

 pressure, so that, if the increased flow be brought about by the 

 vaso-motor mechanisms, it must be by means of nervous channels 

 altering the blood flow in the special arteries of the glands. We 

 know further that emotional conditions, such as hysteria, exist in 

 which an unaccountably great quantity of urine of very low spe- 

 cific gravity is evacuated. 



With regard to the effects of the vaso-motor nerves, we know 

 that section of all the nervous twigs going to the kidneys causes 

 great congestion and an immense increase in the secretion, which 

 commonly contains albumin. This no doubt depends on the sud- 

 den rise in pressure in the glomeruli, owing to the dilatation of 

 the arterioles. If the splanchnics, in which the renal vaso-motor 

 nerves run, be cut, a great quantity of urine is produced from the 

 same cause vaso-motor paralysis but, on account of the large 

 area of vessels injured, the general blood-pressure falls, and there- 

 fore the effect is not so much marked. If the peripheral end of 

 the cut nerves be stimulated, the secretion is diminished, and, 



