564 THE URINE [CH. XXXVII. 



Creatinine with zinc chloride gives a characteristic crystalline 

 precipitate (groups of fine needles) with composition 



C 4 H 7 N 3 O.ZnCl 2 . 



According to the recent researches of G. S. Johnson, urinary 

 creatinine, though isomeric with the creatinine obtained artificially 

 from the creatine of flesh, differs from it in some of 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 produces 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 HgN 3 OHCl) 4 (HgCl 2 ) 3 

 + 2H 2 occurs in the form of minute spheres, quite typical on micro- 

 scopic examination. This compound lends itself very well to quan- 

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

 one-fifth of the weight found is creatinine. 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 urine 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 10 to 16 grammes per diem. These sub- 

 stances 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 phos- 

 phates, 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 



