UREA. 645 



by LoHNSTEiN. 1 JoLLES 2 has also devised a small urinometer for the 

 determination of the specific gravity of small amounts of urine, 20-25 

 cc. The specific gravity may also be determined by the WESTPHAL 

 hydrostatic balance. 



II. ORGANIC PHYSIOLOGICAL CONSTITUENTS OF URINE. 



+ X NH 2 



Urea, Ur, CON 2 H 4 =CO\ > nas been synthetically prepared in sev- 



X NH 2 



eral ways, especially, as WOHLER showed in 1828, by the metameric 

 transformation of ammonium isocyanate: GO.N.NH 4 =CO(NH 2 ) 2 . It 

 is also produced by the decomposition or oxidation of certain bodies 

 found in the animal organism, such as purine bodies, creatine, arginine, 

 other amino-acids, and others. 



Urea is found most abundantly in the urine of carnrvora and man, but 

 in smaller quantities in that of herbivora. In carnivora (dog) the urea 

 nitrogen by abundant protein feeding may amount to 97-98 per cent 

 of the total nitrogen of the urine (SCHONDORFF 3 ) . The quantity in human 

 urine is ordinarily 20-30 p. m. It has also been found in small quantities 

 in the urine of amphibians, fishes, and certain birds. Urea occurs in 

 the perspiration in small quantities, and as traces in the blood and 

 in most of the animal fluids. It also occurs in rather large quantities in 

 the blood, liver, muscle, 4 and bile 5 of sharks. Urea is also found in 

 certain tissues and organs of mammals, especially in the liver, spleen, 

 muscles and others, although only in small amounts. Under pathological 

 conditions, as in obstructed excretion, urea may appear to a considerable 

 extent in the animal fluids and tissues. 



The quantity of urea which is voided in twenty-four hours on a mixed 

 diet is in a grown man about 30 grams, in women somewhat less. While 

 children void less, the excretion relative to their body weight is greater 

 than in grown persons. The physiological significance of urea lies in 

 the fact that this body forms in man and carnivora, from a quantitative 

 standpoint, the most important nitrogenous end-product of the metabolism 

 of protein bodies. On this account the elimination of urea varies to a 

 great extent with the catabolism of the protein, and above all with the 

 quantity of absorbable proteins in the food ingested. The elimination 

 of urea is greatest after an exclusive meat diet, and lowest, indeed less 

 than during starvation, after the consumption of non-nitrogenous sub- 

 stances, since these diminish the metabolism of the proteins of the body. 



1 Pfliiger's Arch., 59; Chem. Centralbl., 1895, 1, and 1896, 2. 



2 Wien. med. Presse, 1897, No. 8. 



3 Pfluger's Arch., 117. 



4 v. Schroeder, Zeitschr. f . physiol. Chem., 14. 



5 Hammarsten, ibid., 24. 



