

URINE. 259 



temperature and subtracted for every three degrees beloiv the nor- 

 mal temperature. For instance, if in using a urinometer calibrated 

 for 15 C. the specific gravity of a urine having- a temperature of 

 21 C. is determined as 1.018 it is necessary to add to the observed 

 specific gravity two units of the third order to obtain the real spe- 

 cific gravity of the urine. Therefore the true specific gravity, at 

 15 C., of a urine having a specific gravity of 1.018 at 21 C. is 

 1.018 + 0.002 = 1.020. 



Pathologically, the specific gravity may be subjected to very 

 wide variations. This is especially true in diseases of the kidneys. 

 In acute nephritis ordinarily the urine is concentrated and of a high 

 specific gravity, whereas in chronic nephritis the reverse conditions 

 are more apt to prevail. In fact under most conditions, whether 

 physiological or pathological, the specific gravity of the urine is in- 

 versely proportional to the volume excreted. This is not true of 

 diabetes mellitus, however, where the volume of urine is large and 

 the specific gravity is also high, owing to the sugar contained in the 

 urine. 



The amount of solids eliminated in the excretion for twenty-four 

 hours may be roughly calculated by means of Long's coefficient, 

 i. e., 2.6. The solid content of 1,000 c.c. of urine is obtained by 

 multiplying the last two figures of the specific gravity observed at 

 25 C. by 2.6. To determine the amount of solids excreted in 

 twenty-four hours if the volume was 1,120 c.c. and the specific grav- 

 ity was 1.018 the calculation would be as follows: 



(a) 18X2.6 = 46.8 grams of solid matter in 1,000 c.c. of 

 urine. 



/z v 46.8 X I 1 2O r 1- j r 



(o) - = ^2.4 grams of solid matter in 1,120 c.c. of 



IOOO 



urine. 



The coefficient of Haser (2.33) which has been in use for years 

 probably gives values that are inaccurate for conditions existing in 

 America. This coefficient was calculated on the basis of the specific 

 gravity determined at a temperature of 15 C. 



Freezing-Point (Cryoscopy). The freezing-point of a solu- 

 tion depends upon the total number of molecules of solid matter 

 dissolved in it. The determination of the osmotic pressure by 

 this method has recently come to be of some clinical importance 

 particularly as an aid in the diagnosis of kidney disorders. In this 

 connection it is best to collect the urine from each kidney separately 

 and determine the freezing-point in the individual samples so col- 



