THE MEANING OF REGULARITIES 93 



more rigorously purified the specimens were, the less constant 

 was their composition, even when material from the same source 

 was compared. In Table 23, a few examples have been chosen from 

 our own work"^"^' ^^. A complete compilation of analytical results 

 has appeared recently^^. No generally applicable regularities in 

 composition seem to impose themselves from such a survey. 



TABLE 23 



COMPOSITION OF SEVERAL PNA PREPARATIONS FROM YEAST AND LFVER* 



* In moles per 100 moles nucleotide. 



It was only after Dr. Elson in our laboratory undertook the 

 study of the ribonucleotide distribution in extracts of the total 

 PNA without further purification^^"^^ that one striking regularity 

 emerged^^' ^^. Whereas none of the other regularities listed before 

 for DNA applied to PNA in a general fashion, one persisted with 

 very few exceptions, namely, the equality of constituents having 

 6-amino groups (adenylic and cytidylic acids) and of those carry- 

 ing 6-keto groups (guanylic and uridylic acids): 6- Am = 6-K. 

 (Compare the frequency distribution of nucleotide ratios in 104 

 PNA samples^^ illustrated in Fig. 9.) I show some typical results 

 in Table 24 compiled from several recent papers^^' ^^' ^^' ^*. 



6. THE MEANING OF REGULARITIES 



I hope I have shown that there is one regularity that almost all 

 nucleic acids, deoxypentose and pentose nucleic acids, appear to 



References p. 98 



