556 



THE EXCRETION OF URINE 



column gives the change in concentration which each constituent under- 

 goes in passing through the renal filter. 



The Amount of Urine 



The amount of urine passed in twenty-four hours varies with the 

 amount of fluid ingested and the proportion of fluid retained by the body 

 or excreted by other channels. Under ordinary conditions a twenty-four- 

 hour sample amounts to from 1000 to 1800 c.c. of urine. On a constant 

 water intake the volume of urine is extremely variable for any single 

 day or part of the day (Addis and Watanabe 3 ). The average volume of 

 urine excreted by twenty individuals on the third, fourth and fifth days 

 of a constant diet in which the fluid intake was 2,070 c.c., varied from 

 1,013 to 1,712 c.c. for a twenty-four-hour period, from 684 to 1,195 c.c. 

 for the first twelve hours of the day, and from 501 to 788 c.c. for the 

 first eight hours of the day. In normal subjects the amount of urine 

 excreted during the night is usually less than that during the day. This 

 is such a constant finding that in cases where more than 50 per cent of 

 the urine is excreted in the twelve hours of the night, suspicions of renal 

 disease should be aroused. 



With a constant intake of food and water, the specific gravity of samples 

 of urine collected at frequent intervals throughout the twenty-four 

 hours exhibits considerable variations. The night urine is usually of 

 higher specific gravity than that of samples passed every two hours 

 during the day, the variation often amounting to as much as ten points. 

 If the variation does not occur, but the different specimens show a fixed 

 specific gravity, either at a high or a low level, it is usually indicative 

 of renal trouble. This is illustrated in the following table: 



