134 Alexander Hollaender and George E. Stapleton 



Escli. coli to protect against mutation production by chemicals 

 or recovery factors. However, it is possible to recognize this 

 only if there is a minimum of population pressure effect. 

 Where the population pressure effect is very great, as in 

 reversion of a tyrosineless strain of Esch. coli, this population 

 pressure will obscure the entire phenomenon of protection 

 and recovery. In contrast to this, the arginineless strain 

 shows decreased mutation rate with increased survival 

 (Hollaender, Billen, and Doudney, 1955). It is important to 

 point out that the recognition of this phenomenon requires 

 careful analysis for each individual mutation. Very similar 

 results have been obtained in regard to chromosome breaks 

 in bean roots, where it has been possible to modify the number 

 of chromosome breaks by chemical treatment after exposure 

 (Wolff and Luippold, 1955). I hope this will be discussed at a 

 later meeting where cytological effects will be brought up. 

 In any case, it is fairly safe to say that the possibility exists 

 of the modification of genetic effects by radiation protection. 



REFERENCES 



Alexander, P., Bacq, Z. M., Cousens, S. F., Fox, M., Herve, A., and 

 Lazar, J. (1955). Radiation Res., 2, 392. 



Alexander, P., Ciiarlesby, A., and Ross, J. (1954). Proc. roy. Soc, 

 223A, 392. 



Bacq, Z. M., Herve, A., Lecomte, J., Fischer, P., and Blavier, J. 

 (1951). Arch. int. Physiol., 59, 442. 



Bashford, R. E., and IIuennekens, F. M. (1955). J. Amer. chem. Soc, 

 77, 3878. 



Burnett, W. T., Jr., and Doiierty, D. G. (1955). Radiation Res., 3, 

 217. 



Burnett, W. T., Jr., Stapleton, G. E., Morse, M. L., and Hollaen- 

 der, A. (1951). Proc. Soc. exp. Biol., N.Y., 77, 036. 



Calvin, M. (1954). Glutathione, A Symposium, p. 3. New York: Acad- 

 emic Press. 



CoNGDON, C. C, Upton, A. C, and Doiiertv, D. G. (1956). In pre- 

 paration. 



Doiierty, D. G., and Burnett, W. T., Jr. (1955). Proc. Soc. exp. Biol., 

 N.Y.,S9, 312. 



Doiierty, D. G., and Siiapira, R. (1956). In preparation. 



Doudney, C. O., and Hollaender, A. (1956). In preparation. 



Hollaender, A., Billen, D., and Doudney, C. O. (1955). Radiation 

 Res., 3, 235. 



