PYRIMIDINE BASES. 193 



which consists in part of leaf-shaped aggregations and in part of cubical 

 or prismatic crystals, often with rounded corners. This compound is 

 used in the microscopic detection of adenine. With the nitric-acid test 

 and with WEIDEL'S reaction adenine acts in the same way as hypoxan- 

 thine. The same is true, for its behavior with hydrochloric acid and 

 zinc with subsequent addition of alkali. 



The procedure for the preparation and detection of the four above- 

 described purine bases is as follows: Boiling with 0.5-1 vol. per cent 

 sulphuric acid, saturating with baryta-water, removing the excess of 

 barium with CCb, precipitating all the bases as silver compounds 

 from the strongly ammoniacal filtrate and dissolving them in boiling 

 nitric acid when the xanthine compound remains in solution on cooling 

 while the combination with the other three bases precipitate. The silver 

 xanthine may be precipitated from the filtrate by the addition of ammonia 

 and the xanthine set free by means of sulphureted hydrogen. The 

 three above-mentioned silver-nitrate compounds are decomposed by sul- 

 phureted hydrogen and the guanine separated from the adenine and 

 hypoxanthine by treatment while hot with ammonia, in which the 

 guanine is soluble with difficulty. When the above filtrate containing the 

 adenine and hypoxanthine, which has been, if necessary, freed from 

 ammonia by evaporation, is allowed to cool, the adenine separates, 

 while the hypoxanthine remains in solution. According to BALKE l 

 we can advantageously precipitate the purine bases with copper sulphate 

 and hydroxylamine. Details for the above methods may be found in 

 complete hand-books. The same procedures are followed in the quan- 

 titative estimation of the purine bases in animal organs. 2 



3. Pyrimidine Bases. 

 These bodies are closely related to the purines, and pyrimidme, 



I I 



CH, may be considered as the mother substance thereof. 



I! II 



N CH 



The pyrimidine bases contained in the nucleic acids are cytosine, uracil 

 and thymine. 



N CNH 2 



I II 

 Cytosine, C4H5NsO, = OC CH (6 amino-2 oxypyrimidine), was first 



I! 



HN CH 



prepared by KOSSEL and NEUMANN from thymus nucleic acid, and then 

 by KOSSEL and STEUDEL and others from various nucleic acids. WHEELER 



*See footnote 1, p. 190. 



2 See Burian and Hall, Zeitschr. f. physiol. Chem., 38; Kossel ibid., 5-8, Bruhns, 

 ibid., 14; His and Hagen, ibid., 30. 



