AVERY, MACLEOD, MCCARTY 



acids of this type must be regarded not 

 merely as structurally important hut as 

 functionally active in determining the 

 biochemical activities and specific 

 characteristics of pneumococcal cells. 

 Assuming- that the sodium desoxvri- 

 bonucleate and the active prmciple are 

 one and the same substance, then the 

 transformation described represents a 

 change that is chemically induced and 

 specifically directed by a known chem- 

 ical compound. If the results of the 

 present study on the chemical nature 

 of the transforming principle are con- 

 firmed, then nucleic acids must be re- 

 garded as possessing biological specifi- 

 city^ the chemical basis of which is as 

 yet undetermined. 



SUMMARY 



1. From Type III pneumococci a 

 biologically active fraction has been 

 isolated in highly purified form which 

 in exceedingly minute amounts is cap- 

 able under appropriate cultural condi- 

 tions of inducing the transformation of 

 unencapsulated R variants of Pneu- 

 mococcus Type II into fully encap- 

 sulated cells of the same specific type 

 as that of the heat-killed microorgan- 

 isms from which the inducing material 

 was recovered. 



2. Methods for the isolation and 

 purification of the active transforming 

 material are described. 



3. The data obtained by chemical, 

 enzymatic, and serological analyses 

 together with the results of prelimi- 

 nary studies by electrophoresis, ultra- 

 centrifugation, and ultraviolet spec- 

 troscopy indicate that, within the 

 limits of the methods, the active frac- 

 tion contains no demonstrable protein, 

 unbound lipid, or serologically reactive 

 polysaccharide and consists princip- 

 ally, if not solely, of a highly polymer- 

 ized, viscous form of desoxyribonu- 

 cleic acid. 



191 



4. Evidence is presented that the 

 chemically induced alterations in cellu- 

 lar structure and function are predic- 

 table, type-specific, and transmissible 

 in series. The various hypotheses that 

 have been advanced concerning the 

 nature of these changes are reviewed. 



CONCLUSION 



The evidence presented supports the 

 belief that a nucleic acid of the desoxy- 

 ribose type is the fundamental unit of 

 the transforming principle of Pneumo- 

 coccus Type III. 



BIBLIOGRAPHY 



L Griffith, F., /. Hyg., Cambridge, Eng., 

 1928, 27:113. 



2. Neufeld, F., and Levinthal, W., Z. hn- 



mimitatsforsch., 1928, 55:324. 



3. Baurhenn, W., Centr. Bakt., 1. Abt., 



Orig., 1932, 126:68. 



4. Dawson, M. H., /. Exp. Med., 1930, 51: 



123. 



5. Dawson, M. H., and Sia, R. H. P., /. Exp. 



Med., 1931, 54:681. 



6. Alloway, J. L., /. Exp. Med., 1932, 55:91; 



1933,57:265. 



7. Berry, G. P., and Dedrick, H. M., J. 



Bact., 1936, 31:50. 



8. Berry, G. P., Arch. Path., 1937, 24:533. 



9. Hurst, E. W., Brit. J. Exp. Path., 1937, 



18:23. Hoffstadt, R. E., and Pilcher, 

 K. S., /. Infect. Dis., 1941, 68:67. Gard- 

 ner, R. E., and Hyde, R. R., /. Infect. 

 Dis., 1942, 71:47. Houlihan, R. B., Proc. 

 Soc. Exp. Biol, and Med., 1942, 51:259. 



10. MacLeod, C. M., and Mirick, G. S., /. 



Bact., 1942, 44:277. 



11. Dawson, M. H., /. Exp. Med., 1928, 47: 



577; 1930, 51:99. 



12. Sevag, M. G., Biochevi. Z., 1934, 273:419. 



Sevag, M. G., Lackman, D. B., and 

 Smolens, J., /. Biol. Chem., 1938, 124: 

 425. 



13. Dubos, R. J., and Averv, O. T., /. Exp. 



Med., 1931, 54:51. Dubos, R. J., and 

 Bauer, J. H., /. Exp. Med., 1935, 62:271. 



14. Liu, S., and Wu, H., Chinese J. Physiol., 



1938, 13:449. 



15. Martland, M., and Robison, R., Biochetn. 



J., 1929, 23:237. 



