THE URINE. 335 



A urine with an alkaline reaction caused by fixed alkalies has a 

 very different diagnostic value than one whose alkaline reaction is 

 caused by the presence of ammonium carbonate. In the latter case 

 we have to deal with a decomposition of the urea of the urine by 

 the action of micro-organisms. 



If we wish to determine whether the alkaline reaction of the 

 urine is due to ammonia or fixed alkalies, we dip a piece of red 

 litmus-paper into the urine and allow it to dry exposed to the air or 

 to a gentle heat. If the alkaline reaction is due to ammonia, the 

 paper becomes red again ; but if it is caused by fixed alkalies, it 

 remains blue. 



The specific gravity of urine, which is dependent upon the 

 relationship existing between the quantity of water secreted and 

 the solid urinary constituents, especially the urea and sodium 

 chloride, may vary considerably, but is generally 1.017-1.020. 

 After drinking large quantities of water it may fall to 1.002, while 

 after profuse perspiration or after drinking very little water it may 

 rise to 1.035-1.040. In new-born infants the specific gravity is low, 

 1.007-1.005. The determination of the specific gravity is an im- 

 portant means of learning the average amount of solids elimi- 

 nated from the organism with the urine, and on this account the 

 determination becomes of true value only when at the same time the 

 quantity of urine voided in a given time is determined. The dif- 

 ferent portions of urine voided in the course of the 24 hours are 

 collected, mixed together, the total quantity measured, and then 

 the specific gravity taken. 



The determination of the specific gravity is most accurately ob- 

 tained with the pyknometer. For ordinary cases the specific grav- 

 ity may be determined with sufficient accuracy by means of 

 areometers. The areometers found in the trade, or urinometers, 

 are graduated from 1.000 to 1.040; for exact observations it is better 

 to use two urinometers, one graduated from 1.000 to 1.020, and the 

 other from 1.020 to 1.040. A special urinometer is that of HELLER, 

 which is graduated according to Baume's scale, from to 8. Each 

 degree corresponds to 7 degrees of the ordinary urinometer, and as 

 the zero-point of HELLER'S urinometer corresponds to the figure 

 1000, then the 1, 1.5, 2, 2.5, 3, etc., degrees of HELLER'S urinometer 

 correspond to 1.007, 1.0105, 1.014, 1.0175, 1.024, etc., of the ordi- 

 nary specific gravity. 



