CHEMICAL BASIS OF THE ANIMAL BODY. 899 



from the carbamate by such alternating processes of oxidation and reduction as 

 may be supposed to take place in the body. The reaction is expressed as fol- 

 lows: 



2. NH 2 .CO.ONH 2 + H 2 = NH 2 .CO.NH 2 + H 2 0. 



Wanklyn 1 and Gamgee, 2 however, since urea, when heated with a large excess 

 of pptassic permanganate, gives off all its nitrogen in a free state, and not in the 

 oxidized form of nitric acid, as do all other amides, conclude that it is not an amide 

 at all, that it is isomeric only and not identical with carbamide. 



It is important to remember that urea is also isomeric with ammonic cyanate, 



C I QNET an( *' i n( * ee d' was fi rst f rme( l artificially by Wbhler (1823) from this 

 body. We thus have three isomeric compounds, ammonium cyanate, urea, and 

 carbamide, related to each other in such a way that urea may be obtained readily 

 either from ammonium cyanate or from ammonic carbamate, and may with the 

 greatest ease be converted into ammonic carbonate. 3 Now urea is a much more 

 stable body than ammonic cyanate, and in the transformation of the latter into the 

 former energy is set free ; and it is worthy of notice that, though the presence of 

 sulphocyanides in the saliva probably indicates the presence of cyanic residues in 

 the body, the nitrogenous products of the decomposition of proteids belong chiefly 

 to the class of amides, cyanogen compounds being rare among them. Pfliiger 4 has 

 called attention to the great molecular energy of the cyanogen compounds, and 

 has suggested that the functional metabolism of protoplasm by which energy is set 

 free may be compared to the conversion of the energetic unstable cyanogen com- 

 pounds into the less energetic and more stable amides. In other words, ammonium 

 cyanate is a type of living, and urea of dead nitrogen, and the conversion of the 

 former into the latter is an image of the essential change which takes place when 

 a living proteid dies. 



Compound ureas. The hydrogen atoms of urea can be replaced by alcohol and acid radicles. 

 The results are compound ureas or ureides when the hydrogen is replaced by an acid radicle. 

 Many of them are called acids, since the hydrogen from the amide group, if not all replaced as 

 above, can be replaced by metal. Thus, the substitution of oxalyl (oxalic acid) gives parabanic 

 acid, 



(CO 

 N J H 2 or CO, NH 2 , N.C 2 O 2 ; 



of tartronyl (tartronic acid), dialuric acid, CO, NH 2 , N.C 3 H 2 O 3 ; of mesoxalyl (mesoxalic acid), 

 alloxan, CO, NH 2 , N.C 3 O 3 . These bodies are interesting as being also obtained by the artificial 

 oxidation of uric acid. (See below.) 



Uric Acid. C 5 H 4 N 4 3 . 



The chief constituent of the urine in birds and reptiles ; it occurs only sparingly in 

 this excretion in man and most mammalia. It is normally present in tne spleen, 

 and traces of it have been found in the lungs, muscles of the heart, pancreas, brain, 

 and liver. Urinary and renal calculi often consist largely of this body or its salts. 

 In gout, accumulations of uric acid salts may occur in various parts of the body, 

 forming the so-called gouty concretions. 



It is when pure a colorless, crystalline powder, tasteless, and without odor. 

 The crystalline form is very variable, but usually tends toward that of rhombic 

 tables. 5 When impure it crystallizes readily, but then possesses a yellowish or 

 brownish color. In water it is very insoluble (1 in 14,000 or 15,000 of cold water) ; 

 ether and alcohol do not dissolve it appreciably. On the other hand, sulphuric 

 acid takes it up without decomposition, and it is also readily soluble in many 

 salts of the alkalies, as in the alkalies themselves. Ammonia, however, scarcely 

 dissolves it. 



1 Arch. f. Physiol., 1880, S. 550. 



2 Journ. Chem. Soc., 2, vol. vi. p. 25. 



3 The following literature is interesting in connection with the question of the cyanic or amide 

 origin of urea-Drechsel : Ber. d. k. s. Gesell. d. Wiss., Leipzig, Sitz. 25 Juli, 1875 ; Arch. f. Pbysiol., 

 1880, S. 505. v. Knieriem : Zt. f. Biol., Bd. x. (1874), S. 263. Munk : Zt. f. physiol. Chem., Bd. ii. 

 (1878), S. 29. E. Salkowski : Centralbl. f. d. med. Wiss., 1875, No. 58; Ber. d. Deutsch. Chem. Ge- 

 sell., 1875, S. 116. Zeitsch. f. physiol. Chem., Bd. i. (1877), Sn. 1 u. 374 ; Bd. iv. (1880), Sn. 54 u. 103. 

 Schmiedeberg : Arch. f. exp. Pathol., Bd. viii. (1877), S. 1. 



* Pfliiger's Archiv., Bd. x. (1875). S. 337. 



6 See Ultzmann and K. B. Hoffmann, Atlas der Harnsedimente, Wien, 1872. 



