1881.] Mr Roy, On the mechanism of the renal secretion. 115 



still more so according as it is applied to a splanchnic nerve or to 

 a sensory nerve, e.g. for the peripheral end of the splanchnic it may 

 be less than half a second while the same current applied to the 

 central end of the sciatic of the same animal may give a latent 

 period of three seconds or even very much longer. 



18. As a rule it is difficult to sever completely all the nerve 

 fibres which accompany the renal vessels so that stimulation of 

 the peripheral end of the splanchnic will no longer cause a con- 

 striction of the vessels of the kidney, but great differences in this 

 respect occur in different animals. While with some animals, 

 section of all the nerve trunks which are visible to the naked eye 

 will suffice for this purpose, with others it is only after the most 

 laborious and minute cleaning of the walls of the vein and artery 

 that vasoconstrictor influences no longer pass to the kidney on 

 stimulation of the splanchnic. 



19. When these nerves have been completely severed stimu- 

 lation of the peripheral end of the cut splanchnic no longer causes 

 a contraction but an expansion of the renal vessels which goes 

 hand in hand with the rise of the blood-pressure. 



20. The secretion of urine increases or diminishes caeteris 

 paribus with the degree of expansion of the renal vessels. 



21. The renal vessels expand or contract with great readiness 

 to relatively slight changes in the chemical constitution of the 

 blood. For example, the injection into the veins of even a very 

 small quantity of water (1-2 c.cm. in the case of a medium-sized 

 dog) causes a contraction of the kidney varying in amount and 

 lasting from 1-2 seconds to 2-3 minutes, and which is succeeded 

 by a more or less well marked expansion of the kidney lasting for 

 a much longer time than the contraction. 



22. Injection of a small quantity of \ per cent, salt .solution 

 causes a primary expansion of the renal vessels varying in degree 

 with the amount of the fluid injected, with the individual, and 

 with the condition of the individual at the time of injection. 



23. Urea in ^ per cent, or in 5 or 10 per cent, solution 

 causes a primary constriction of the renal vessels followed by a 

 more or less powerful expansion of longer duration. Digitalis 

 causes also a primary contraction, differing however from urea in 

 the fact that this contraction is of longer duration, but resembling 

 it in so far that it is followed by a secondary expansion. A certain 

 number of other diuretics resemble water, urea and digitalis in 

 causing a primary contraction with diminution or arrest of secre- 

 tion, followed by expansion and increased secretion. 



24. Other diuretics again, such as nitrate of soda, acetate of 



