CYTOSINE. 189 



tative determination of the purines in feces. Details for the above 

 methods may be found in complete hand-books. The same procedures 

 are followed in the quantitative estimation of the purine bases in animal 

 organs. 1 



3. Pyrimidine Bases. 



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

 N=CH 



C 4 H 4 X2, = HC CH, may be considered as the mother substance thereof. 



i-. 



; CH 



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

 and thymine. 



HN CNH 2 



fl II 

 Cytosine, C 4 H5lS r 3O,^=OC CH (6 amino-2 oxy pyrimidine), was first 



N=CH 



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

 KOSSEL and STEUDEL and others from various animal nucleic acids, and 

 finally also by WHEELER and JOHNSON from triticonucleic acid. WHEELER 

 and JOHNSON 2 have also prepared it synthetically. It is transformed 

 into uracil by the action of nitrous acid. 



The free base is difficultly soluble in water (129 parts) and crystallizes 

 In thin leaves with a mother-of-pearl luster. It is insoluble in ether 

 and difficultly soluble in alcohol. The double compound with platinum 

 chloride, the crystalline picrate, the nitrate, and the two sulphates are 

 of importance in the detection of cytosine. This base is precipitated 

 by phosphotungstic acid and by silver nitrate in the presence of an 

 excess of barium hydroxide, which fact is of importance in the detection 

 of cytosine (KUTSCHER). The double bismuth-potassium iodide gives 

 a brick-red precipitate. Cytosine gives the murexid reaction with 

 chlorine-water and ammonia (see Chapter XV), and also the reaction 

 described by WHEELER and JOHNSON under uracil. In regard to 

 preparation see KOSSEL and STEUDEL 3 and also KuTSCHER. 4 



1 See Burian and Hall, Zeitschr. f. physiol. Chem., 38; Kossel and Wulff, ibid., 17; 

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



2 Amer. chem. Journ., 29. 



3 Zeitschr. f. physiol. Chem., 37 and 38. 



4 Ibid., 38. As it is not excluded, but rather probable according to Wheeler, 

 that besides thymine also other related pyrimidine bases such as isocytosine, 6-amino 

 pyrimidine and 6-oxpyrimidine can be formed in the hydrolytic cleavage of the nucleic 

 acids, Wheeler has prepared salts and compounds of these bodies and described them 

 as a matter of comparison, Journ. of biol. Chem., 3. 



