140 WALTEIt JOKES 



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

 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 ^ hexose (formic acid and 

 levulinic acidj are formed by hydrolysis of (lie nucleic acid. 



C G H 1S O 6 CII,CO.CH 2 CO 2 H + HC0 2 H 



levulinic acid 



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

 Of Thymus Nucleic Acid Of Yeast Nucleic Acid 



1. Phosphoric acid Phosphoric Acid 



Purine Derivatives 



2 . G u a nine Gua nine 



3. Adenine Adenine 



Pyrimidine Derivatives 



4. Cytosine Cytosine 



5. Thymine Uracil 



Carbohydrate 



6. Ilexose Pentese 



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

 striking, especially in connection with 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 he 

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

 acid, and in such a study one must be careful lost 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 hitter 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. 



