6 J. N. DAVIDSON AND E. CHARGAFF 



in the cell, histochemical tests have been of great value [Chapter 17]. For 

 example, the Feulgen nucleal reaction,^^ which is specific for deoxypentose 

 nucleic acid, has been used to demonstrate that this type of nucleic acid is 

 confined to the cell nucleus. Similarly the Brachet""^* histochemical test 

 with ribonuclease [Chapter 17] has demonstrated the presence of pentose 

 nucleic acid in the cell cytoplasm, in obviously abundant amounts in such 

 tissues as liver." In Caspersson's ultraviolet technique no distinction is 

 made between the two types of nucleic acid, but material which absorbs 

 ultraviolet light strongly and which is Feulgen-negative is considered to 

 be pentose polynucleotide. 



The general conclusions from histochemical tests have been confirmed by 

 the procedure of cell disruption with separation of the morphological com- 

 ponents of the cells, as described in Chapters 18 and 21. The cytoplasmic 

 components contain pentose nucleic acid while the nuclei contain deoxypen- 

 tose nucleic acid and small amounts of pentose nucleic acid [Chapter 18]. 

 We may therefore conclude that both types of nucleic acid are present 

 in all types of cell, both plant and animal, and that the main biological 

 distinction between pentose nucleic acid and deoxypentose nucleic acid is 

 that the former is mainly cytoplasmic while the latter is exclusively, or al- 

 most exclusively, nuclear. The designations "chromonucleic" and "plasmo- 

 nucleic acids" have been proposed for deoxypentose and pentose nucleic 

 acids, respectively," • ^^ but these names are not widely used. 



The study of nucleic acids entered a new stage when the application of 

 paper chromatography to the separation of nucleic acid constituents (pu- 

 rines, pyrimidines, nucleosides, nucleotides) made possible precise analytical 

 investigations with very small amounts of materiaP^"^' [Chapters 7, 10, and 

 11]. The introduction of ion-exchange chromatography [Chapter 6] repre- 

 ss J. N. Davidson and C. Waymouth, Proc. Roy. Soc. Edinburgh B62, 96 (1944). 

 " A. W. Pollister and A. E. Mirsky, Nature 152, 692 (1943). 

 "8 A. W. Pollister and A. E. Mirsky, Nature 153, 711 (1944). 

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

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

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



62 E. Vischer and E. Chargaff, /. Biol. Chem. 176, 703, 715 (1948) . 



63 E. Chargaff, Experientia 6, 201 (1950); J. Cellular Comp. Physiol. 38, suppl. 1, 41 

 (1951); Federation Proc. 10, 654 (1951). 



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

 66 J. N. Davidson, Ann. Rev. Biochem. 18, 155 (1949). 

 66 G. Schmidt, Ann. Rev. Biochem. 19, 149 (1950). 

 6' J. Baddiley, Ann. Rev. Biochem. 20, 149 (1951). 



68 D. O. Jordan, Ann. Rev. Biochem. 21, 207 (1952). 



69 G. B. Brown, Ann. Rev. Biochem. 22, 141 (1953). 



76 J. N. Davidson, "The Biochenustry of the Nucleic Acids," 2nd ed. Methuen, 

 London, 1953. 



