DIFFERENTIAL DISTRIBUTION ANALYSIS 137 



release of bunched pyrimidine sequences. A more than tentative 

 formulation of the reaction mechanism will, however, have to 

 await a better understanding of the fate of the free deoxyribose 

 residues liberated in the initial stage of the removal of purines by 

 acid. 



b. Nucleotide arrangement in analytically indistinguishable 

 deoxyribonucleic acids of different cellular origin 



It happens quite often that deoxyribonucleic acids of taxonomi- 

 cally entirely different origin exhibit identity of composition as 

 regards the distribution of the nitrogenous constituents (compare 

 the example of the deoxyribonucleic acids of the sheep and the 

 salmon cited previously^ *^). In such cases, the method of differen- 

 tial distribution analysis discussed in this survey is destined to be 

 of great value. It permits the examination of detailed features of 

 the nucleotide arrangement, far beyond the possibilities of dis- 

 tinction offered by total constituent analysis. I have selected, for 

 inclusion in Table 28, three examples of nucleic acid fractions 

 that cannot be distinguished analytically. There can be little 

 doubt about the entirely different sequential plans governing the 

 structure of these polymers if the values for the abundance of 

 solitary pyrimidine units are compared. 



c. Nucleotide arrangement in different deoxyribonucleic 

 acids of animal origin 



Table 29 compares the distribution findings obtained with total, 

 unfractionated preparations of the deoxyribonucleic acids from 

 calf thymus, human spleen, and sperm preparations from two sea 

 urchin species. These data do not exhaust the information gathered 

 by us on different animal nucleic acids^^, but are presented 

 here to indicate the scope of the method. 



d. Nucleotide arrangement in the total deoxyribonucleic acid 

 of rye germ and in a complete series of fractions 



The use of a deoxyribonucleic acid from a plant source offers 

 several advantages. These nucleic acids have been shown to con- 



References p. 159 



