INTRODUCTION 3 



and by Levene^ from thymus nucleic acid, while Ascoli*'' in 1900 isolated 

 uracil from yeast nucleic acid. 



II. The Two Types of Nucleic Acid 



The work of these early pioneers in nucleic acid chemistry, Miescher, 

 Kossel, Neuman, Steudel, O. Hammarsten, and others, is fully described 

 in the books by Jones," Feulgen,^^ and Levene and Bass,^^ and no more need 

 be said about it here. By 1930, however, a definite picture had emerged of 

 two definite types of nucleic acid. One of them, the nucleic acid from yeast, 

 on hydrolysis yielded adenine, guanine, cytosine, uracil, phosphoric acid, 

 and a sugar recognized by 0. Hammarsten as a pentose and identified by 

 Levene and Jacobs" as ribose. The other, the nucleic acid from thymus, 

 yielded adenine, guanine, cytosine, thymine, phosphoric acid, and a sugar 

 at first thought to be a hexose but later shown by Levene'^ to be a deoxy- 

 pentose and identified as deoxyribose.'^ These two nucleic acids, therefore, 

 came to be called ribonucleic acid and deoxyribonucleic acid, respectively, 

 and, since most nucleic acids of animal origin appeared to resemble that 

 from thymus, while the triticonucleic acid isolated from wheat embryo by 

 Osborne and Harris'^ was similar to that from yeast, the assumption was 

 made that pentose nucleic acids were characteristic of plants and deoxy- 

 pentose nucleic acids of animal tissues."' " The terms phytonucleic acid 

 and zoonucleic acid were suggested for these two groups, respectively. '^ 



This classification, however, was never free from objection since it had 

 been known from the end of the last century that pentose derivatives were 

 present in animal tissues. In 1894, for example, 0. Hammarsten'* prepared 

 from pancreas tissue a "i3-nucleoprotein" from which Bang'^ obtained a 



9 P. A. Levene, Z. physiol. Chem. 37, 402 (1902-3). 



1" A. Ascoli, Z. physiol. Chem. 31, 161 (1900-1901). 



" W. Jones, "Nucleic Acids — Their Chemical Properties and Physiological Con- 

 duct," 2nd ed. Longmans Green & Co., London, 1920. 



12 R. Feulgen, "Chemie und Physiologic dei Nukleinstoffe," Borntraeger, Berlin, 

 1923. 



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

 York, 1931. 



1* P. A. Levene and W. A. Jacobs, Ber. 42, 2102, 2469, 2474, 2703 (1909). 



>* P. A. Levene and E. S. London, /. Biol. Chem. 81, 711 (1929); 83, 793 (1929). 



i« P. A. Levene, L. A. Mikeska, and T. Mori, /. Biol. Chem. 85, 785 (1930). 



" T. B. Osborne and I. F. Harris, Z. physiol. Chem. 36, 85 (1902). 



>8 O. Hammarsten, Z. physiol. Chem. 19, 19 (1894). 



'« I. Bang, Z. physiol. Chem. 26, 133 (1898-99); 31, 411 (1900-1901). 



