CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 



659 



disregarded. Further, the distension of the blood vessels will in 

 general depend on the constriction or dilation of the renal arteries 



FIG. 89. SEMI-DIAGKAMMATIC SECTIONAL VIEW OF ONCOGBAPH. Half natural size. 

 K tube connecting instrument with oncometer. J) piston floating on oil contained 

 in the cavity M ; the oil is prevented from escaping by the side of the piston by the 

 delicate flexible membrane E, which does not interfere with the movements of the 

 piston. H, recording lever connected with the piston by a needle G passing through 

 the guides F, F'. The screw C is for the purpose of clamping the edge of the membrane 

 between the two ring-shaped surfaces at N, while the side tube L is for the purpose 

 of filling the instrument. 



and their ramifications, for distension due to venous obstruction 

 will only occur in special cases. Hence variations in the volume 

 of the kidney may be taken as a measure of variations in its 

 vascular supply, increase of volume indicating dilated renal 

 vessels, and decrease of volume indicating constriction of the renal 

 vessels. 



When by means of the instrument just described a tracing is 

 taken of the volume of a kidney in what may be considered a 

 normal condition, some such result as that shewn in Fig. 90 is 

 obtained. 



The volume of the kidney is seen to be so delicately responsive 

 to changes in the mean arterial pressure that the curve reproduces 

 almost exactly a blood-pressure curve, shewing not only the 

 respiratory undulations, but even the rise and fall due to the 

 individual heart-beats. With each rise of mean arterial pressure 

 more blood is driven into the renal vessels and the kidney swells : 

 with each fall of pressure less blood enters and the kidney shrinks. 

 On other tracings taken in the same way may often be seen (not 

 shewn in Fig. 90) the wider variations corresponding to the 



422 



