CH. XXXIX.] 



COMPOSITION OF URINE 



583 



1. During digestion. Here there is a formation of free acid in 

 the stomach, and a corresponding liberation of bases in the blood, 

 which, passing into the urine, diminish its acidity, or even render it 

 alkaline. This is called the alkaline tide ; the opposite condition, the 

 acid tide, occurs after a fast for instance, before breakfast. 



2. In herbivorous animals and vegetarians. The food here con- 

 tains excess of alkaline salts of acids such as tartaric, citric, malic, etc. 

 These acids are oxidised into carbonates, which, passing into the urine, 

 give it an alkaline reaction. 



Specific Gravity. The specific gravity varies inversely as the 

 quantity of urine passed under normal conditions from 1015 to 

 1025. A specific gravity below 1010 should excite suspicion of 

 hydruria; one over 1030, of a febrile condition, or of diabetes, a 

 disease in which it may rise to 1050. The specific gravity has, 

 however, been known to sink as low as 1002 (after large potations, 

 urina potus), or to rise as high as 1035 (after great sweating) in 

 perfectly healthy persons. 



Composition. The following table gives the average amounts of 

 the urinary constituents passed by a man taking an ordinary diet 

 containing about 100 grammes of protein in the twenty-four hours : 



Total quantity of urine 



Water . 



Solids . 



Urea 



Uric acid 



Hippuric acid . 



Sodium chloride 



Phosphoric acid 



Sulphuric acid 



Ammonia 



Creatinine 



Chlorine . 



Potassium 



Sodium . 



Calcium . 



Magnesium 



1500-00 grammes. 

 1440-00 

 60-00 

 35-00 



0-75 



1-05 

 16-5 



3-5 



2-0 



0-65 



0-9 

 11-0 



2-5 



5-5 



0-26 



0-21 



The most abundant constituents of the urine are water, urea, and 

 sodium chloride. In the foregoing table one must not be misled by 

 seeing the names of the acids and metals separated. The acids and 

 the bases are combined to form salts, such as urates, chlorides, 

 sulphates, phosphates, etc. 



Urea. 



Urea, or Carbamide, CO(NH 2 ) 2 , is isomeric (that is, has the same 

 empirical, but not the same structural formula) with ammonium 

 cyanate (NHJCNO, from which it was first prepared synthetically 

 by Wohler in 1828. Since then it has been prepared synthetically 

 in other ways. Wohler's observation derives interest from the fact 



