CHEMISTRY OF THE LEUCOMAINES. 281 



So far as the genesis of most of the leucoma'ines is 

 concerned, we know very little, though GtATJTIEe is of the 

 belief that they are being formed continuously and inces- 

 santly in the animal tissues side by side with the forma- 

 tion of urea and carbonic acid and at the expense of the 

 nitrogenous elements. It is quite probable, as Kossel has 

 pointed out, that some of these products are in themselves 

 antecedents of end-products of metabolism. This is unques- 

 tionably true of the imido group, which exists in the ade- 

 nine and guanine molecules, and through vital or putre- 

 factive processes is split off, giving rise to ammonia, which 

 in turn serves to form urea and uric acid. Botjchard has 

 sought an explanation of the presence of these bases in the 

 urine, by supposing that they were originally formed in 

 the intestinal tract, from which they were absorbed into the 

 system, to be subsequently eliminated by the kidneys. This 

 view has also been brought forward by Schab (1886), who 

 holds that these bases, which may be formed by putrefactive 

 changes in the intestinal tract, are absorbed into the circu- 

 latory system, whence they may be partly eliminated by 

 the kidneys or may be partly deposited in the tissues them- 

 selves. 



The views of Bouchard and Schae have, to a certain 

 extent, been confirmed by the investigations of Udeanszky 

 and Baumann, who showed that the well-known ptomaines, 

 cadaverine and putrescine, occur in the urine in cystinuria, 

 and are formed by putrefactive changes induced in the in- 

 testinal tract probably by specific microorganisms. Under 

 this same head fall the recent observations of WoLKOW 

 and Batjmann, that alkapton is produced from tyrosin by 

 similar changes in the intestines. The origin of the true 

 leucoma'ines cannot, however, be accounted for in this 

 manner, for they are indissolubly connected with the meta- 

 bolism of the cell itself, and are, therefore, formed in the 

 tissues and organs proper, especially those rich in nucleated 

 cells. 



Another source of the nitrogenous bases must not be 

 lost sight of, and that is protoplasm itself. The researches 

 of Deechsel, Siegfeibd, and Schulze have shown that 



