vii KATABOLIC CONSTITUENTS OF UEINE 385 



-ONH 4 

 -NH 2 



Schmiedeberg is the author of the theory that urea is derived 

 from ammonium carbonate. He demonstrated that on treating 

 protein with barium hydrate ammonium carbonate is formed, which 

 when injected into the body is (at least partly) converted into urea 

 with loss of two molecules of water. The theory that urea may 

 be formed from the dehydration of ammonium carbamate is due to 

 Drechsel (1875), who showed that ammonium carbamate is formed 

 on oxidising leucine and glycocoll. When an aqueous solution of 

 these substances is exposed to the electrolytic action of 4-6 Grove 

 cells (with an automatic commutator, by which the direction of the 

 current can be rapidly changed, so as to produce at each electrode 

 alternate processes of reduction and oxidation), it is converted 

 through an intermediate product into urea : 



ONH 4 



+H0 



Ammonium carbamate. Intermediate product. 



ONH 2 /NH, 





C0< +H 2 =CO< +H 2 



\NH 2 \NH 2 



Urea. 



This theory of the derivation of urea either from ammonium 

 carbonate or from ammonium carbamate, by successive and 

 alternate oxidations and reductions taking place in the liver, has 

 been substantially confirmed by the experiments of v. Schroder, 

 Salomon and Minkowski, as also by those of Nencki, Hahn, 

 Pawlow and Massen, on dogs with an Eck's fistula, to which we 

 referred in Chapter V. (p. 335). Taken as a whole, the results of 

 these experiments show the hypotheses of Schmiedeberg and 

 Drechsel to be justified, and further make it probable that carbamic 

 acid and ammonium carbonate are katabolic products from the 

 spleen, pancreas, and gland cells of the intestinal tract, which, 

 when absorbed and carried by the portal system to the liver, are 

 converted into urea. 



On another theory, maintained by Hoppe- Seyler, urea is 

 derived from cyanic acid. This is founded on the fact that part of 

 the amino-acids (leucine, tyrosine, glycocoll) introduced into the 

 body, appear in the urine in combination with the group (CONH) 

 or cyanic acid, forming the so-called uramino-acids (Salkowski, 

 Hoppe-Seyler, Baumann). This fact leads the above authors to 

 conjecture that cyanic acid can be formed in the body. On this 



VOL. II 2 C 



