416 CHEMISTRY OF THE LEUCOMAINS. 



would seem as if the latter view was the correct one. The reason 

 for this belief is twofold. In the first place the hydrolytic process 

 is so energetic that adenin and presumably the other purin bases as 

 well are completely broken up. Again, if the pyrimidin bodies 

 are antecedents, it might be expected that on feeding to animals 

 purin bodies would be eliminated in the urine. Steudel (1901), how- 

 ever, has shown that a number of synthetic pyrimidin bodies can 

 be given to the dog with the result that some of these are destroyed 

 while others are eliminated as such, and at no time are purin bodies 

 formed. Thymin, a natural pyrimidin body, is split up and yields 

 urea, whereas its isomer the synthetic methyl uracil is excreted un- 

 changed. 



Steudel's investigation further shows that the di- and tri-amino 

 derivatives of pyrimidin are highly toxic, while the others are not. 

 These poisonous substances yield insoluble compounds which are 

 deposited in the tubules of the kidney. It is noteworthy that the 

 really only poisonous natural purin body is adenin which, as already 

 shown, is 6-amino purin (see pages 341, 350). It would seem as 

 if the introduction of the amino group into the purin or pyrimidin 

 nucleus rendered such bodies poisonous. 



Thymin. — In 1893, Kossel and Neumann showed that the nu- 

 cleinic acid from the thymus gland of the calf on boiling with dilute 

 sulphuric acid yields a crystalline body (8 per cent.) which they des- 

 ignated as thymin. At first they ascribed it the formula C^^^^f)^ 

 but subsequent investigations showed that the original preparations 

 were not pure and that thymin was CjHgNjOj . 



Thymin was also obtained by Kossel and Neumann by similar 

 hydrolysis of the nucleinic acid of ox spleen. The " nucleosin " 

 which Miescher isolated from a nucleinic acid derived from the sper- 

 matozoa of the salmon is according to Kossel identical with thymin. 



In 1896 Kossel isolated it from the spermatozoa of the sturgeon 

 and three years later Gulewitsch obtained it from the testicles of the 

 herring. Its possible presence in the auto-digestion of the pancreas 

 has been indicated by Levene. Kutscher obtained thymin and pos- 

 sibly uracil in the auto-digestion of thymus glands. Fischer and 

 Roeder^ in 1901 prepared thymin and uracil synthetically. 



Thymin forms four or six-sided colorless plates resembling those 

 of cholesterin and is doubly refractive. Illustrations of these are 

 given by Gulewitsch {Zdt. physiol. Chem., 27, 295). On careful 

 heating it can be sublimed and, as Kossel has shown, its presence in 

 nucleinic acid can thus be directly demonstrated" by heating some of 

 the acid between two watch glasses. The melting point is above 

 290°. When heated rapidly it sinters at 318° and melts at about 

 321° with evolution of gas becoming yellowish (Fischer and 

 ^Berichte, 34,3751, 4129. 



