ORGANIC PHYSIOLOGICAL CONSTITUENTS. 679 



ing is then made from the point where this curved line coincides with 

 the scale of the urinometer. If the eye is not in the same horizontal 

 plane with the convex line of the meniscus, but is too high or too low, 

 the surface of the liquid assumes the shape of an ellipse, and the reading 

 in this position is incorrect. Before reading, press the urinometer gently 

 down into the liquid and then allow it to rise, and wait until it is at rest. 



Each urinometer is graduated for a certain temperature, which, 

 at least in the case of the better ones, is marked on the instrument. 

 If the urine is not at the proper temperature, the following corrections 

 must be made: For every three degrees above the normal temperature 

 one unit of the last order is added to the reading, and for every three 

 degrees below the normal temperature one unit (as above) is subtracted 

 from the specific gravity observed. For example, when a urinometer 

 graduated for 15 C. shows a specific gravity of 1.017 at 24 C., then the 

 specific gravity at 15 C. = 1.017+0.003 = 1.020. 



When great exactitude is required, as, for instance, a determina- 

 tion to the fourth decimal point, we make use of a urinometer constructed 

 by LoriNSTEiN. 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. 



H. ORGANIC PHYSIOLOGICAL CONSTITUENTS OF URINE. 



+ X NH 2 



Urea, Ur, CO^H* = CO^ , has been synthetically prepared in sev- 



N NH 2 



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

 transformation of ammonium isocyanate: CO.N.NH4 = CO(NH2)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 other substances. 



Urea is found most abundantly in the urine of carnivora 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, even in rather large quantities. 

 Urea is also found in certain tissues and organs of mammals, especially 



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



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

 8 Pfluger's Arch., 117. 



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



5 Hammarsten, ibid., 24. 



