560 THE URINE. [CH. xxxvn. 







its properties, such as reducing power, solubility, and character 

 of its gold salts. The reducing action of urinary creatinine has 

 led to some confusion, for some physiologists have supposed that 

 the reducing action on Fehling's solution and picric acid of normal 

 urine is due to sugar, whereas it is really chiefly due to creatinine. 

 The readiest way of separating creatinine from urine is the 

 following : To the urine a twentieth of its volume of a saturated 

 solution of sodium acetate is added, and then one-fourth of its 

 volume of a saturated solution of mercuric chloride : this pro- 

 duces an immediate abundant precipitate of urates, sulphates, 

 and phosphates, which is removed by filtration ; the filtrate is 

 then allowed to stand for twenty-four hours, when the precipitation 

 of a mercury salt of creatinine (C 4 H 5 HgN30H01)4(HgCl 2 )3+ 2H 2 

 occurs in the form of minute spheres, quite typical on microscopic 

 examination. This compound lends itself very well to quantita- 

 tive analysis. It may be collected, dried, and weighed, and 

 one-fifth of the weight found is creatiniue. Creatinine may be 

 obtained from it by suspending it in water, decomposing it 

 with sulphuretted hydrogen, and filtering. The filtrate deposits 

 creatinine hydrochloride, from which lead hydrate liberates 

 creatinine. An important point in Johnson's process is that all the 

 operations are carried out in the cold ; if heat is applied one obtains 

 the creatinine of former writers, which has no reducing power. 



The Inorganic Constituents of- Urine. 



The inorganic or mineral constituents of iirine are chiefly 

 chlorides, phosphates, sulphates, and carbonates ; the metals with 

 which these are in combination are sodium, potassium, ammonium, 

 calcium, and magnesium. The total amount of these salts varies 

 from 19 to 25 grammes daily. The most abundant is sodium 

 chloride, which averages in amount i o to 1 6 grammes per diem. 

 These substances are derived from two sources first from the 

 food, and secondly as the result of metabolic processes. The 

 chlorides and most of the phosphates come from the food ; the 

 sulphates and some of the phosphates, as a result of metabolism. 

 The salts of the blood and of the urine are much the same, with 

 the important exception that, whereas the blood contains only 

 traces of sulphates, the urine contains abundance of these salts. 

 The sulphates are derived from the changes that occur in the 

 proteids of the body ; the nitrogen of proteids leaves the body 

 as urea and uric acid ; the sulphur of the proteids is oxidised to 

 form sulphuric acid, which passes into the urine in the form 

 of sulphates. The excretion of sulphates, moreover, runs parallel 

 to that of urea. 



