THE ORGANIC CONSTITUENTS OF THE URINE. 227 



among the laboring-classes, etc., but I should certainly look upon 

 the average merchant or student, who leads a sedentary life, as an 

 overfed individual if his daily elimination of urea should exceed 30 

 grammes in the twenty-four hours. Among the well-to-do classes 

 I find that an elimination of from 20 to 25 grammes is probably 

 normal, taking the body- weight of the person into due considera- 

 tion. A smaller amount even is not infrequently met with in people 

 of sedentary habits who are in perfect health, but I should scarcely 

 regard such a quantity as normal for the average laboring-man. 

 While extensive variations in the amount of urea are thus observed 

 in health, still greater deviations from average figures are noted in 

 disease, but here as there we must always take into account the 

 amount of nitrogen that is ingested and the body weight. 



An increase in. the elimination of urea, referable to the destruction 

 of organized albumins, is here frequently observed, but may be 

 obscured, owing to a deficient ingestion of nitrogen, unless the amount 

 of the latter is known. At this place, however, it is scarcely neces- 

 sary to enter into pathological considerations, and I must refer the 

 reader to other works for detailed information on such questions. 

 But I may briefly recall that in certain diseases of the liver in 

 which an extensive destruction of the parenchyma is taking place 

 the amount of urea may be greatly diminished, although a fairly 

 abundant supply of nitrogenous food is ingested. As has been 

 shown, the synthetic formation of urea is here seriously impeded, 

 and as a result we find that a considerable proportion of the urinary 

 nitrogen then appears in the form of ammonium salts of paralactic 

 acid, of carbamic acid and carbonic acid, and in extreme cases, 

 indeed, mono-amido acids, such as leucin and tyrosin, may be found. 



Properties of Urea. Urea crystallizes in two forms, viz., in 

 long, fine white needles if rapidly formed, or in long, colorless 

 rhombic prisms when allowed to crystallize more slowly from its 

 solutions. 



It melts at 130 to 132 C., but is probably decomposed already 

 at a temperature of 100 C. It is readily soluble in water and 

 alcohol, but is insoluble in anhydrous ether, chloroform, and benzol. 

 As the substance is an acid amide, its solutions present a neutral 

 reaction. 



In accordance with its character as an unsaturated amide of 

 carbonic acid, however, it combines with acids to form crystalline, 

 salt-like compounds. The most important of these are the nitrate 

 and the oxalate. 



Urea nitrate, CO(NH 2 ) 2 .HNO 3 , crystallizes in two forms, viz., in 

 delicate rhombic, horizontal platelets, which are commonly arranged 

 overlapping in a shingle-like manner when rapidly formed, or as 

 thicker rhombic columns or plates when allowed to crystallize more 

 slowly. 



. Urea nitrate is readily soluble in distilled water, but dissolves 

 with difficulty if this is acidulated with nitric acid, and also in 



