THE NUCLEINIC ACIDS. 99 



(see Uric Acid), the intimate relation which exists between 

 pyrimidin and cytosin, on the one hand, and purin and the purin 

 derivatives on the other is at once apparent. It is quite likely 

 indeed that cytosin represents the mother-substance of the purin 

 group. These relations are expressed by the following formulae : 



(1)N C(6) 



(2)0 0(5) 



(3)N=C(4) 

 Pyrimidin radicle. 



NH C.NH, 



CO CH 



i. 



in 



Cytosin. Uric acid. 



Reactions. Nitrous acid transforms cystosin into uracil, according 

 to the equation : 



C 4 H 5 N 3 O + HNO 2 =s= C 4 H 4 N 2 O 2 -f 2N + H 2 O 

 Cytosin. Uracil. 



On oxidation with barium permanganate cytosin yields biuret 

 and oxalic acid : 



C 4 H 5 N 3 + 4O + H 2 O == C 2 H 5 N 3 2 + C 2 H 2 O 4 

 Cytosin. Biuret Oxalic acid. 



Like many other pyrimidin derivatives, cytosin on treating with 

 freshly prepared chlorine water and the subsequent addition of a 

 trace of ammonia and the application of heat, gives a red color 

 (murexid reaction). 



On treating a dilute solution of cytosin with a few drops of a 

 concentrated neutral solution of silver nitrate, needles of a double 

 salt crystallize out on standing, which are soluble with difficulty in 

 cold water and resemble kreatinin silver nitrate in appearance. 



Uracil. It has been pointed out in the foregoing section that 

 cytosin yields uracil on treating with nitrous acid. It has therefore 

 been suggested that uracil possibly does not occur preformed in the 

 nucleinic acid complex, but is merely a secondary product. Osborne, 

 who first encountered uracil among the decomposition-products of 

 tritico-nucleinic acid, expressed the opinion, that possibly the sub- 

 stance might occupy an analogous position in the vegetable world as 

 thymin does in animal tissues. As a matter of fact Ascoli could 

 also demonstrate uracil among the cleavage-products of yeast, 

 nucleinic acid. More recently, however, Kossel and Steudel also 

 obtained the substance from thymo-nucleinic acid and the spermato- 

 nucleinic acid derived from the testicles of the herring. 



Structurally it is 2.6 dioxypyrimidin ; its relation to cytosin is 

 apparent from the formula? : 



