BIOLOGICAL ROLE OF DEOXYPENTOSE NUCLEIC ACIDS 



449 



TABLE II 

 Bacterial Transformations Effected In Vitro with DNA Preparations 



e. Biological Nature of Transformation 



Only a fraction of the cells present are permanently modified in a bac- 

 terial transformation. The fraction has been given as 0.2 to 5.0 % in cultures 

 of pneumococcus** and from 0.01 to 0.05% in. Hemophilus.''^- ^^ These 

 yields are gradually being raised by improvements in the efficiency of the 

 process so that yields of over 15 % have recently been obtained with pneu- 

 mococcus.** Qualitatively, there appears to be a sharply defined alter- 

 ation in the properties of those cells which have been transformed. 

 One may ask in what way this alteration is related to a mutation and to 

 the normal genetic mechanisms of the bacteria. 



(1) Parallels between Genes and Transjorming Agents. If transforming 



93 R. D. Hotchkiss, Exptl. Cell Research Suppl. 2, 383 (1952). 

 •o" H. E. Taylor, Compt. rend. 228, 1258 (1949). 



