146 



WALTER JONES 



thymine 



Another point of difference between the two nucleic acids is in resj 

 to their carbohydrate group. The carbohydrate group of yeast nucleic 

 acid is a pentose group, and a pentose is formed by hydrolysis of the nu- 

 cleic acid ; but the carbohydrate group of thymus nucleic acid is a hexose 

 group, and the decomposition products of a hexose (formic acid and 

 levulinic acid) are formed by hydrolysis of the nucleic acid. 



C H 12 6 - CH 3 CO.CH 2 C0 2 H 



levulinic acid 



HCOH 



The fundamental groups of the two nucleic acids are therefore as follows 



Of Thymus Nucleic Acid Of Yeast Nucleic Acid 



Phosphoric acid Phosphoric Acid 



1. 



2. 

 3. 



Guanine 

 Adenine 



4. Cytosine 



5. Thymine 



6. Hexose 



Purine Derivatives 



Pyrimidine Derivatives 



Carbohydrate 



Guanine 

 Adenine 



Cytosine 

 Uracil 



Pentose 



This fundamental identity or analogy of the two nucleic acids is very 

 striking, especially in connection wi+h their curious and parallel hydro- 

 lytic conduct; and it strongly suggests that the two nucleic acids have a 

 similar chemical constitution. Such a question, however, can only be 

 decided by a study of the partial decomposition products of thymus nucleic 

 acid, and in such a study one must be careful lest he fall into the "argu- 

 ment in a circle." Thus, the constitution of thymus nucleic acid may 

 be assumed in the beginning ? and from this assumed constitution, that of 

 its decomposition products may be inferred. The latter may then be used 

 to prove the constitution of the nucleic acid. The matter is mentioned 

 here, not, in disparagement of the work that has been done with the prod- 

 ucts of the partial hydrolysis of thymus nucleic acid, but because the 

 writer believes that the logical fallacy indicated has occurred in the orig- 

 inal discussion of the subject. 



