THE URINE. 



[CH. xxxvu. 



urochrome. It shows no absorption bands. It is probably an 

 oxidation product of urobilin. (Riva, A. E. Garrod.) 



Reaction. The reaction of normal urine is acid. This is not 

 due to free acid, as the uric and hippuric acids in the urine are 

 combined as urates and hippurates respectively. The acidity is 

 due to acid salts of which acid sodium phosphate is the most impor- 

 tant. Under certain circumstances the urine becomes less acid 

 and even alkaline ; the most important of these are as follows : 



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 

 contains excess of alkaline salts of acids like tartaric, citric, malic, 

 <fec. These acids are oxidised into carbonates, which passing into 

 the urine give it an alkaline reaction. 



Specific Gravity. This should be taken in a sample of the 

 twenty-four hours' urine with a urinometer. 



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 in the twenty-four 

 hours : 



Total quantity of urine 



Water 



Solids .... 



Urea 



Uric acid 



Sodium chloride 



Phosphoric acid . 



Sulphuric acid. 



Ammonia 



Creatinine 



Chlorine 



Potassium 



Sodium 



Calcium . 



Magnesium . 



1500^00 grammes. 



6o - oo 

 35-00 



075 

 16-5 



3'5 



2'O 

 0-65 



5'5 

 0-26 



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

 and sodium chloride. In the foregoing table one must not be 



