484 HANDBOOK OF PHYSIOLOGY. 



It has been found that the kidney is extremely sensitive to any 

 alteration in the general blood-pressure, every fall in the general blood- 

 pressure being accompanied by a decrease in the volume of the kidney, 

 and every rise, unless produced by considerable constriction of the 

 peripheral vessels, including those of the kidney, being accompanied by 

 a corresponding increase of volume. Increase of volume is followed 

 by an increase in the amount of urine secreted, and decrease of volume 

 by a decrease in the secretion. In addition, however, to the response of 

 the kidney to alterations in the general blood-pressure, it has been 

 further observed that certain substances, when injected into the blood, 

 will also produce an increase in volume of the kidney, and consequent 

 increased flow of urine, without affecting the general blood-pressure 



Fig. 308. Roy's Oncograph, or apparatus for recording alterations in the volume of the kidney, 

 etc., as shown by the oncometer a, upright, supporting recording lever I, which is raised or lowered 

 by needle 6, which works through/, and which is attached to the piston e, working in the chamber 

 rf, with which the tube f rom the oncometer communicates. The oil is prevented from being squeezed 

 out as the piston descends by a membrane, which is clamped between the ring-shaped surfaces of 

 cylinder by the screw i working upward; the tube h is for filling the instrument. 



such bodies as sodium acetate and other diuretics. These observations 

 appear to prove that local dilatation of the renal vessels may be produced 

 by alterations in the blood acting upon a local nervous mechanism, as this 

 happens when all of the renal nerves have been divided. The altera- 

 tions are not only produced by the addition of drugs, but also by the in- 

 troduction of comparatively small quantities of water or saline solution. 

 To this alteration of the blood acting upon the renal vessels (either 

 directly or) through a local vaso-motor mechanism, and not to any great 

 alteration in the general blood-pressure, must we attribute the effects of 

 meals, etc., observed by Roberts. The renal excretion is increased after 

 meals and diminished during fasting and sleep. The increase begins 

 within the first hour after breakfast, and continues during the succeed- 

 ing two or three hours; then a diminution sets in, and continues until 

 an hour or two after dinner. The effect of dinner does not appear until 



