150 THE URINE. 



The importance of a knowledge of the specific gravity 

 is rather to detect marked changes in the urine from a 

 series of observations than to be able to infer the presence 

 of some abnormal constituent, like glucose, which would 

 certainly be found by the subsequent tests. Thus, in 

 nephritis a decrease in specific gravity without change in 

 the volume indicates that the urea is not being excreted 

 and that uremia may be feared. 



336. Test the accuracy of the urinometer in water, 

 then take the specific gravity of urine. The cylinder must 

 be wide enough for the urinometer to float in it without 

 touching. Foam on the liquid should be removed by a 

 piece of filter-paper. 



337. Test with an accurate urinometer the difference 

 in specific gravities of freshly-passed urine when at a tem- 

 perature of from 95 to 98 F. and that at 60 F. or below. 



The reaction of normal mixed human urine passed 

 during twenty-four hours is acid. Quantitative determina- 

 tions of the salts in the urine show that the bases (kations) 

 are not present in large enough amounts to replace all the 

 hydrogen of the acids. This fact is commonly expressed in 

 the statement that the acid reaction is due to acid salts, 

 principally acid phosphates of sodium and potassium. 

 However, since these as well as the other inorganic com- 

 pounds are more or less dissociated, it is preferable to say 

 that the hydrogen ions (hydrions) cause the acidity. The 

 administration of alkaline drugs is followed by the urine's 

 becoming less acid or even alkaline. The same effect is 

 produced by vegetable foods. These contain the potas- 

 sium salts of organic acids citric, malic, tartaric, and 

 others which are oxidized to potassium carbonate in the 

 system. A similar result is brought about a short time 

 after a hearty meal, when hydrochloric acid is being set 



