THE KIDNEYS AND URINE. 367 



apparatus (oncograph) capable of recording graphically, with a writing 

 ICYCT, such variations. It lias 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 fur- 

 ther observed that certain substances, when injected into the blood, will 

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

 now of urine, without affecting the general blood-pressure such bodies 

 as sodium acetate and other diuretics. These observations appear to prove 

 that local dilatation of the renal vessel^ may be produced by alterations 

 in the blood upon a local nervous mechanism, as the effect is produced 

 when all of the renal nerves have been divided. The alterations are not 

 only produced by the addition of drugs, but also by the introduction of 

 comparatively small quantities of water or saline solution. To this altera- 

 tion 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 effect of meals, etc., ob- 

 served by Roberts. "The renal excretion is increased after meals and 

 diminished during fasting and sleep. The increase began within the first 

 hour after breakfast, and continued during the succeeding two or three 

 hours; then a diminution set in, and continued until an hour or two after 

 dinner. The effect of dinner did not appear until two or three hours after 

 the meal; and it reached its maximum about the fourth hour. From this 

 period the excretion steadily decreased until bedtime. During sleep it 

 sank still lower, and reached its minimum being not more than one- 

 third of the quantity excreted during the hours of digestion." The in- 

 creased amount of urine passed after drinking large quantities of fluid 

 probably depends upon the diluted condition of the blood thereby in- 

 duced. 



The following table 1 will help to explain the dependence of the filtra- 

 tion function upon the blood-pressure and the nervous system: 



Table of the Relation of the Secretion of Urine to Arterial Pressure. 



A. Secretion of Urine may be increased 



a. By increasing the general blood-pressure, by 



1. Increase of force or frequency of heart-beat. 



2. Constriction of small arteries of areas other than the kidney. 



1 Modified from M. Foster. 



