ADVANCED DEMONSTRATIONS 305 



lever can be made to break a circuit in which an electric signal is set. 

 The signal writes on the kymograph. Thus the arterial pressure, the 

 renal volume, and the secretion of urine are simultaneously recorded. 



FIG. 255. Arterial pressure (1) and oncometer tracing (2) of kidney volume. Be- 

 tween the points starred the 10th dorsal root was excited. The time is marked in 

 seconds. (Bradford.) 



So long as the venous pressure is constant any increase in renal 

 volume will denote increased blood-pressure in and increased blood- 

 flow through the kidney. The secretion of urine varies as the 

 volume of blood passing through the kidney per minute. (By 

 dividing the renal nerves and exciting the spinal cord or vaso- 

 motor centre the greatest rate of blood-flow through the kidney can 

 be produced.) Ligature of the renal vein stops the secretion of 

 urine. After a temporary obstruction albuminous urine is secreted. 

 Half a grain of citrate of caffeine injected intravenously will produce a 

 fall of arterial pressure and a preliminary contraction of the kidney, 

 followed by great expansion and increased flow of urine. 



Plethysmography of the Arm. The arm is placed in the glass 

 plethysmograph, which is made to fit closely to the upper part of the 

 forearm. The junction is made air-tight by means of a rubber collar 

 or bandage and vaseline. The plethysmograph is connected with a 

 recording tambour, a j_-piece being interposed. Record the volume 

 curve on a moderately fast drum. The tracing shows pulse waves and 

 respiratory oscillations. 



Note the effect of a deep inspiratory and a forced expiratory effort. 

 The effects are produced by the emptying and congestion of the veins 



