308 ERWIN CHARGAFF 



a. Thymic Acid 341 



b. Apurinic Acid 341 



(1) Preparation 341 



(2) Properties 342 



3. "Cores" (Limit Polynucleotides) 345 



VI. Constituents of Deoxypentose Nucleic Acids 345 



1. Sugar 346 



2. Nitrogenous Constituents 346 



3. Unidentified Constituents 347 



VII. Composition of Deoxypentose Nucleic Acids 348 



1. General 348 



2. Procedures 350 



3. Distribution of Purines and Pyrimidines 350 



a. Grouping of Deoxypentose Nucleic Acids and Presentation of Results 350 



b. Composition Differences and Similarities 351 



VIII. Fractionation of Deoxypentose Nucleic Acids 358 



1. General 358 



2. Fractional Dissociation of Nucleohistone or Protein Nucleates ... 361 

 IX. Composition Studies and Structural Investigations 366 



X. Correlations and Concluding Remarks 368 



1. Simplifying Generalizations 368 



2. Unifying Generalizations 369 



3. A Concluding Remark 371 



I. Introductory Remarks 



The early history of the discovery of the deoxypentose nucleic acids 

 (DNA) has been mentioned in Chapter 1 of this book. A much lengthier, 

 and in part pleasantly autobiographical, treatment will be found in Levene's 

 admirable monograph;^ and the later stages were touched upon, though in 

 considerably less detail, by several authors.^"* The fascinating correspond- 

 ence which forms part of the collected papers of F. Miescher^ must, how- 

 ever, be specially mentioned in a review of this subject. 



An account — not practicable in the present framework — of the evolu- 

 tionary sequence of our understanding of the nucleic acids would not be 

 uninstructive: it would show how often in the natural sciences, even behind 

 seemingly trivial experiments, there lies an entire vision of nature; it would 

 demonstrate that the answers which the investigator receives often are 

 contained in the questions he asks. As long as, in the field under considera- 

 tion here, feeble and faltering questions were asked, the answers were vague; 



>P. A. Levene and L. W. Bass, "Nucleic Acids." The Chemical Catalog Company, 



New York, 1931. 

 2 J. M. Gulland, G. R. Barker, and D. O. Jordan, Ann. Rev. Biochem. 14, 175 (1945). 

 ' E. Chargaff and E. Vischer, Ann. Rev. Biochem. 17, 201 (1948). 

 ^ E. Chargaff, Experientia 6, 201 (1950). 

 * "Die histochemischen und ph^'siologischen Arbeiten von Friedrich Miescher. 



Gesammelt und herausgegeben von seinen Freunden," 2 Vols. F. C. W. Vogel, 



Leipzig, 1897. 



