522 THE EXCRETION OF URINE 



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. 



The Specific Gravity of Urine 



In urine collected at different times of the day the specific gravity may 

 show a variation of ten points. Indeed, the specific gravity of the urine 

 has been taken as a functional test by clinicians. With a constant food 

 and water intake the variations found in the specific gravity of samples 

 of urine taken al two-hour periods in normal and pathological conditions 

 are very useful as criteria of the functional state of the kidney. Fixa- 

 tion of the specific gravity at cither a low or a high figure is not the 

 usual normal finding. The following figures will illustrate; 



