174 NUCLEIC ACIDS AND THE NITROGENOUS BASES 



which, until its discovery among the decomposition-products of nucleic 

 acids, was unknown in nature. It is now not only recognized as the 

 carbohydrate radical of plant nucleic acid, but also regarded as the only 

 pentose which normally occurs in animal tissues. In two nucleic 

 acids found in animal tissues, but possibly traceable to a vegetable 

 origin, namely Inosinic Acid and Guanylic Acid, d-ribose also constitutes 

 the carbohydrate radical, but the nucleic acid which is most charac- 

 teristic of animal tissues, Thymus Nucleic Acid, so called because of 

 the circumstance that it was first prepared in a pure condition from 

 the tissues of the thymus, yields Levulinic Acid on hydrolysis by acids. 

 Now levulinic acid, or /3-acetyl propionic acid: 



CH 3 CO.CH2.CH 2 .COOH 



is formed when Hexoses are boiled with mineral acids, Formic Acid 

 being produced at the same time: 



C 6 Hi 2 O 6 = C 6 H 8 O 3 + HCOOH + H 2 O 



In the hydrolysis of thymus nucleic acid by mineral acids, formic 

 acid is produced as well as levulinic acid. It is evident, therefore, 

 that both of these products are derived from a Hexose radical in the 

 nucleic acid and confirmation of this inference is supplied by the fact 

 that on oxidation of thymus nucleic acid with nitric acid, Saccharic 

 Acid is included among the products, and saccharic acid must have a 

 hexose precursor: 



2C 6 Hi 2 O 6 -}-3O 2 =2C 6 HioO 8 +2H 2 O 



Among the Nitrogenous Bases which result from the acid hydrolysis 

 of nucleic acids, Guanine and Adenine, which are Purine Bases, are 

 found in both animal and plant nucleic acids, but among the Pyrimidine 

 Bases which are yielded by the two classes of nucleic acid, there is a 

 difference, for while both types of nucleic acid yield Cytosine, the animal 

 nucleic acid ("thymus nucleic acid") yields Thymine, and vegetable 

 nucleic acid yields Uracil. 



The pyrimidine bases are heterocyclic compounds which are dis- 

 tinguished by the possession of the following nucleus: 



I 



Pyrimidine itself has the formula: 



N 



HC 



