ISOLATION AND COMPOSITION OF DEOXYPENTOSE NUCLEIC ACIDS 349 



difficult, dull, controversial. The center begins to be surrounded by enor- 

 mous analytical slums: it is a world of decimals. 



The problem of the recognition of identity and diversity in high-molecu- 

 lar cell constituents has been discussed before.'' Here, it will suffice to point 

 out that a chemical comparison with respect to identity or difference must 

 be based on the nature and the proportions of the constituents, on the 

 sequence in which these constituents are arranged in the molecule, and on 

 the type and the position of the linkages that hold them together. The 

 smaller the number of components of such a macromolecule is, the greater 

 is the difficulty of a decision. Deviations of the analytical results from 

 simple, integral proportions, of no importance for substances of small size, 

 become very significant when applying to compounds whose molecular 

 weights range in the millions; and variations in the proportions of their 

 several constituents often will provide the only proof of the occurrence of 

 different compounds. 



The existence of significant chemical differences between deoxy pentose 

 nucleic acids of different cellular origin, or what has been called the chemical 

 specificity of nucleic acids,^ was discovered only a few years ago."^ Soon 

 after, it was possible to formulate most of the regularities that are recog- 

 nized today.'*'" -^' The steps that permitted this relatively ver^' rapid 

 progress were the following. After the development of partition chromatog- 

 raphy on filter paper and its qualitative application to amino acids'^^ it 

 became obvious that the high and specific absorption in the ultraviolet of 

 the purines and pyrimidines could form the basis of a quantitative ultra- 

 micromethod, if proper procedures for the hydrolysis of the nucleic acids 

 and for the complete separation of the hydrolysis products could be found. 

 Such procedures were indeed developed, 2"-''® and the elaboration of de- 

 tailed methods^^*"^^* was soon followed by their application to the analysis 

 of several nucleic acids.""* '"'^^^ The description of an arrangement per- 

 mitting the easy demonstration of the purine and pyrimidine spots^^^ and 

 the application of a similar, commercially available, ultraviolet lamp"" 

 facilitated the performance of analyses. A photographic method useful for 

 the preservation of permanent records was also described.^*' "^ 



2« E. Chargaff, J. Cellular Camp. Physiol. 38, Suppl. 1, 41 (1951). 



2« R. Consden, A. H. Gordon, and A. J. P. Martin, Biochem. J. 38, 224 (1944). 



2" E. Vischer and E. Chargaff, J. Biol. Chem. 168, 781 (1947). 



"» E. Vischer and E. Chargaff, Federation Proc. 7, 197 (1948). 



2" R. D. Hotchkiss, J. Biol. Chem. 175, 315 (1948). 



2« E. Vischer and E. Chargaff, J. Biol. Chem. 176, 703 (1948). 



"9 E. R. Holiday and E. A. Johnson, Nature 163, 216 (1949). 



2" E. Chargaff, B. Magasanilc, R. Doniger, and E. Vischer, J. Am. Chem. Sac. 71, 



1513 (1949). 

 "' R. Markham and J. D. Smith, Nature 163, 250 (1949). 

 2" R. Markham and J. D. Smith, Biochem,. J. 45, 294 (1949). 



