EXCRETION 



467 



inished blood-supply to the kidney and a diminution in the amount of urine 

 ecreted. The second condition is brought about by contraction of the 

 enal artery alone and possibly by a simultaneous dilatation of the efferent 

 'essels of the glomeruli. Moreover the pressure in the vessels of the glomer- 

 .li may be varied according to the degree of contraction or relaxation of the 

 uscle coat of the afferent and efferent vessels. See Fig. 211 and the ac- 

 :ompanying explanation. 



Coincident with the rise and fall of pressure in the glomerular capillaries 

 :here is a rise and fall in the rate of urinary flow. Thus it has been found that 

 ,n increase in the aortic pressure from 127 to 142 mm. of mercury, from 

 igation of the carotid, femoral, and vertebral arteries, increased the rate of 

 .rinary flow from 8.7 grams in thirty minutes to 21.2 grams. On the 

 contrary, a decrease in aortic pressure below 40 mm. of mercury caused by 

 ivision of the spinal cord is followed by a total abolition of the urinary flow, 

 'hese facts serve to indicate the dependence of the secretion on blood- 

 oressure. 



The period of functional activity of the kidney is accompanied by an 

 increase in the volume of blood flowing through it as is evident from an in- 



FIG. 212. SCHEME OF A RENAL ONCOMETER OR PLETHYSMOGRAPH. K, kidney; RT, receiving 

 tambour or capsule; PB, pressure bottle; PR, recording piston. 



spection of the organ. At this time it is enlarged, swollen, and red in color. 

 The blood in the renal vein is bright red in color and contains more oxygen 

 and less carbon dioxid than venous blood generally. During the intervals 

 of activity the kidney is supplied with a less amount of blood and hence it 

 diminishes in size, becomes pale in color and the blood of the renal vein 

 becomes dark and venous in character. These variations in the volume of 

 the kidney have also been experimentally determined and registered by 

 means of the oncometer and oncograph devised by Roy. 



The Renal Oncometer. The oncometer consists of a metallic capsule, 

 (Fig. 212) composed of halves which open and close by means of a hinge. 

 The capsule encloses two thin membranous and distensible sacs. These are 

 connected with a piston recorder by means of a tube. The kidney, with- 

 drawn from the body, is placed within the oncometer. Through an opening 

 in the side pass the artery, vein, and ureter. A thin light oil is then poured 

 through a side tube from a pressure bottle until the membranous sacs 

 are completely filled and surround the kidney on all sides. When the 



