ISOLATION AND COMPOSITION OF DEOXYPENTOSE NUCLEIC ACIDS 



369 



conclude that there is no subunit of recognizably recurrent structure larger- 

 than a mononucleotide. 



2. Unifying Generalizations 



The fear of premature generalizations, though justified on the whole, is 

 not without its own risk. By insisting only on the differences between the 

 various deoxypentose nucleic acids, of which there are many, one may not 

 see the unity for the decimals. The deoxypentose nucleic acid molecules 

 appear to possess no perceptible periodicity of their constituents: the nucleo- 

 tide sequence is probably arrhythmic. If some recurrent features exist, we 

 have no means of discerning them, as a bird's-eye view of this giant throw 

 of dice requires a distance which is denied us. It is, therefore, the more sur- 

 prising that the inspection of even the earliest analytical results compelled 

 the recognition of several regularities which, since the time when they were 

 first proposed,* have become well established: (a) The sum of the purine 

 nucleotides equals that of the pyrimidine nucleotides, (b) The molar ratio of 



ADENINE 



30 - 



20 



10 





OSPM 



THYMINE 



GUANINE Cr TO SINE 





OSPM 



OSPM 



OSPM 



Fig. 7. Proportions of nitrogenous constituents (per 100 g. -atoms of phosphorus) 

 in the deoxyribonucleic acids of the ox (O), sheep (S), pig (P), and man (M). (Taken 

 from ChargafT and Lipshitz.'") 



