EXCRETION 



467 



secreted at a pressure of 60 mm. of mercury from the low- 

 pressure blood of the second set of renal capillaries as from the 

 high-pressure blood of the glomeruli. By obstruction the mole- 

 cular concentration of the urine is diminished to half or three- 

 quarters of the normal. 



The Influence of the Circulation on the Secretion of 

 Urine. Although the activity of no organ in the body is 

 governed more by the indirect effects of nervous action than 

 that of the kidney, no proof has been given of the existence of 

 secretory fibres for it comparable to those of the salivary glands. 

 All the changes in the rate of renal secretion which follow the 

 section or stimulation of nerves can be explained as the conse- 

 quences of the rise or fall of local or general blood-pressure, and 

 of the corresponding 

 variations in the 

 velocity of the blood 

 in the renal vessels. 



The best way to 

 study variations in 

 the calibre of the 

 renal vessels is the 

 pie thysmo graphic 

 method, and the onco- 

 meter of Roy is a 

 plethysmograph 

 adapted to the kid- 

 ney. It consists of a 

 metal capsule lined 

 with loose membrane, 

 between which and 

 the metal there is a 

 space filled with oil. 

 The two halves of the 

 capsule open and shut 

 on a hinge ; and the 

 kidney, when intro- 

 duced into it. is sur- 

 rounded on all sides by the membrane, the vessels and ureter 

 passing out through an opening. The oil-space is connected with a 

 cylinder also filled with oil, above which a piston, attached to a lever, 

 moves. The lever registers on a drum the changes in the volume of 

 the kidney i.e., practically the changes in the quantity of blood in 

 it, and therefore in the calibre of its vessels. A still better oncometer 

 is that of Schafer, in which air is employed instead of oil. 



Nerves of the Kidney. Both vaso-constrictor and vaso-dilator 

 fibres for the renal vessels, but most clearly the former, have been 

 shown to leave the cord (in the dog) by the anterior roots of the sixth 

 thoracic to second lumbar nerves, and especially of the last three 

 thoracic. They run in the splanchnics, and then through the renal 

 plexus around the renal artery into the kidney. The vaso- 

 constrictors predominate, so that the general effect of stimulation of 

 the nerve-roots, the splanchnics, or the renal nerves is shrinking of 



302 



FIG. 175. DIAGRAM OF ORGAN-PLETHYSMOGRAPH 

 OR ONCOMETER. 



B, metal box in two halves opening on the hinge 

 H ; M, thin membrane ; A, space filled with oil ; 

 O, organ enclosed in oneometer ; V, vessels of organ ; 

 /, tube for filling instrument with oil ; T, tube con- 

 nected with D, which opens into cylinder C ; C is 

 also filled with oil ; P, piston attached by E to a 

 writing lever. 



