344 RADIATION BIOLOGY 



SO early. Clearly, this is of fundamental importance for any theory of 

 radiobiological action. 



The differences among the curves of Figs. 6-1 and 6-2 indicate that at 

 least five distinct mechanisms are involved in the nine different effects 

 described. On the other hand, four of the curves (haploid yeast, diploid 

 yeast, bacterial spores, fern spores) are quite similar, thus indicating that 

 the same or very similar mechanisms may be operating in all these cases. 

 It is to be hoped that future investigations may supply additional effec- 

 tiveness curves over a wide range of LET, thus revealing whether these 

 curves belong to a relatively small or an indefinitely large number of 

 distinct types. 



No general theory of the radiobiological operation(s) of LET has been 

 published. In view of the complexity of the subject, this is not surprising. 

 Comments and suggestions concerning certain aspects of its role in 

 specific radiobiological actions have been made by various authors (e.g., 

 Dale et al, 1949; Fano, 1942; Lea, 1947a; Tobias, 1950; Zirkle, 1940, 

 1950; Zirkle and Tobias, 1953). 



REFERENCES 



(Information regarding availability of government documents indicated by an aster- 

 isk may be obtained from the Office of Technical Services, Department of Commerce, 



Washington, D.C.) 



(Daggers designate investigations in which LET was varied by less than a factor of 5 



and no influence of LET was observed.) 



Aebersold, P. C, and J. H. Lawrence (1942) The physiological effects of neutron 



rays. Ann. Rev. Physiol., 4: 25-48. 

 Allen, A. O. (1947) Radiation chemistry of aqueous solutions. J. Phys. Colloid 



Chem., 52: 479-490. 

 Axelrod, Dorothy, P. C. Aebersold, and J. H. Lawrence (1941) Comparative effects 



of neutrons and X rays on three tumors irradiated in vitro. Proc. Soc. Exptl. 



Biol. Med., 48: 251-256. 

 Bonet-Maury, P., and M. Lefort (1948) Formation of hydrogen peroxide in water 



irradiated with X- and alpha-rays. Nature, 162: 381-382. 

 Catcheside, D. G., and D. E. Lea (1943) The effect of ionization distribution on 



chromosome breakage by X rays. J. Genetics, 45: 186-196. 

 Crabtree, H. G., and L. H. Gray (1939) The influence of wavelength on the bio- 

 logical effectiveness of radiation. Brit. J. Radiology, 12: 39-53. 

 Dale, W. M., L. H. Gray, and W. J. Meredith (1949) The inactivation of an enzyme 



(carboxypeptidase) by X- and a-radiation. Phil. Trans. Roy. Soc. (London), 



A242: 33-62. 

 Dempster, E. R. (1941) Dominant vs. recessive lethal mutation. Proc. Natl. Acad. 



Sci. U.S., 27: 249-250. 

 fDognon, A. (1924) Influence de la longueur d'onde sur la floculation d'une solution 



colloidale par les rayons X. Compt. rend. soc. bioL, 91: 197-199. 

 Eberhardt, K. (1943) Vergleich der chromosomenbruchauslosenden Wirkung von 



Rontgen- und Neutronstrahlen bei Drosophila melanogaster. Naturwissen- 



schaften, 31: 23. 

 Enzmann, E. V., and C. P. Haskins (1939) Note of modifications in the morpho- 



