206 ALEXANDER IIOLLAENDER 



diij^lication. This effect is not as visible after chromosome cUiplication, 

 but there are some very basic questions which still liave to be answered. 

 Parmnecium lends itself to careful investigation in this field. 



All these studies establish that it is possible to manipulate living cells 

 in regard to survival, rate of mitosis, chromosome breaks, and nuitation 

 production. If we analyse carefully what takes place in these cells and 

 if we use modern tools, such as tritiated thymidine to detect DNA 

 synthesis and metabolic inhibitors to influence protein and nucleic acid 

 synthesis and energy metabolism, we can follow the steps leading from 

 the initial absorption of the radiation energy to the final chromosome 

 break, rejoining of chromosomes, or establishment of a mutation. It 

 appears now that these different j^rocesses lend themselves to practical 

 manipulation. These studies will afford us, with the cooperation of the 

 biochemists, a much better picture of how radiation damage is initiated 

 and how it will express itself. Such a line of investigation will also give 

 VIS possible tools to study the synthesis of proteins and nucleic acids — 

 the area where probably our greatest development will take place. 



REFERENCESt 



Gaulden, Mary E. (1956). Genetics 41, 645. 



HoLLAENDER, A., and McCarthy A. Marie ( H)59). Science 130, J 420. 



HoL^LAENDER. A., and Stapleton G. E. (1956). In. "Peaceful Uses of Atomic Energy", 

 Proc. Int. Conf., Geneva, Aug. 1955, Vol. II. p. 311. United Nations, New York. 



Kauemank, B. p., Hollaender, A., and Gay, H. (1946). Genetics 31, 349. 



Kimball, R. F., Gaither, Nenita, and Wilson, Stella M. (1959). Proc. nat. Acad. 

 Sci. Wash. 45, 833. 



KiMB.^LL, R. F., Gaither Nenita, and Perdue Stella W. (1961). Int. J. Radn Biol. 

 3, 133! 



Kirby-Smith, J. S., Nicoletti, B.. and Gwyn, Mitzi L. (1960). Genetics, 45, 996. 



Stapleton, G. E. (1960). In, "Radiation Protection and Recovery", p. 87. (A. Hollaen- 

 der, ed.). Pergamon Press, Oxford. 



SwANSON, C. P., and Hollaender, A., (1946). Proc. nat. Acad. Sci., Wash. 32, 295. 



Wolff, S. (1960). Jn, "Radiation Protection and Recovery", p. 157. (A. Hollaender, 

 ed.). Pergamon Press, Oxford. 



t For further references on this subject see volume: "Radiation Protection and Re- 

 covery" (A. Hollaender, ed.). Pergamon Press, Oxford, 1960. 



DISCUSSION 



alexjCnder: Have you the data which would explain why the doses necessary 

 for inhibition of mitosis vary so widely from one cell to another? In mammals 

 and in some cultures we have not seen any effects of radiation on mitosis within 

 the first 24 hr aft^er the exposure, even when 300 r were applied. 



HOLLAENDER : There is an interesting j^aper in which a similar effect of irradiation 

 on the mitotic rate in the skin cells of the mouse ear was established. Radiation 

 doses here were greater but they were not too high. Dr. Karson very elegantly 

 studied this problem on grasshopper neuroblasts. He observed chromosome 

 damage in living cells. I think it could not be done so easily on mammalian 

 tissues. 



