THE SECRETION OF URINE. 



413 



When by means of the instrument just described a tracing is taken of 

 the volume of a kidney in what maybe considered a normal condition, some 

 such result as that shown in Fig. 112 is obtained. 



FIG. ill. 



Semi-diagrammatic Sectional View of Oncograph. (Half natural size.) K, tube connecting 

 instrument with oncometer; D, piston floating on oil contained in the cavity M; the oil is pre- 

 vented 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 Awhile the side tube L is for the 

 purpose of filling the instrument. 



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, showing not only the respiratory undulations 



FIG. 112. 



BLOOD PRESSURE 



KIDNEY CURVE 



Blood -pressure Tracing, and Curve from Renal Oncometer. (Natural size.) The blood-pres- 

 sure abscissa line has been raised 2.75 cm. (the actual medium blood-pressure having been 115 

 mm. Hg.). The time-curve gives interruptions recurring every three seconds. 



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 



