356 SPECULATIONS ON CELLULAR ACTIONS 



in the same unit. This is particularly true of measurements of alpha 

 rays, beta rays, high-energy electrons, fast neutrons, and x-rays and 

 gamma rays of either very low or very high energy. When we consider 

 that in many investigations of rate of energy transfer, one of our most 

 useful modifying factors, some or all of these radiations must be em- 

 ployed, the handicap is obvious, and we must appeal to the physicists to 

 eliminate it. 



With regard to measurement of effect, the situation is much worse. 

 In the first place, reproducibility is usually poor; even in favorable cases, 

 reproducibility within 5 per cent may be considered relatively good. 

 This may be improved by better control of environmental and genetic 

 factors and the utilization of more favorable mechanisms, as discussed 

 above, in quantitative studies. In the second place, measurements of 

 effect are usually slow and laborious. This, it seems to me, is one of our 

 chief obstacles in radiobiological research because it forces each in- 

 vestigator to speciahze in one or a few end effects and thus narrows his 

 experience and outlook. I have no specific suggestions; I can only urge 

 that time and ingenuity be expended in speeding up the measurement 

 of various effects, so that the output of each available investigator may 

 be multiplied throughout his all-too-brief productive period. 



REFERENCES 



i. Timofeeff-Ressovsky, N. W., and K. G. Zimmer, Das Trefferprinzip in der Bi- 

 ologic, Hirzel, Berlin, 1947. 



2. Griffith, H. D., and K. G. Zimmer, Brit. J. Radiol, 8: 40-47, 1935. 



3. Zirkle, R. E., Radiology, 52: 846-855, 1949. 



4. Read, J., Brit. J. Radiol, 22: 366, 1949. 



5. Wyckoff, R. W. G., J. Exptl. Med., 52: 769-780, 1930. 



6. Lea, D. E., R. B. Haines, and E. Bretscher, /. Hyg., 41: 1-16, 1941. 



7. Zirkle, R. E., and C. A. Tobias, unpublished. 



8. Giles, N. H., Jr., Proc. Natl. Acad. Sci., 26: 567-574, 1940. 



9. Thoday, J. M., J. Genetics, 43: 189-210, 1942. 



10. Stapleton, G. E., A. HoUaender, and Frances L. Martin, to appear in supplement 

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12. Zirkle, R. E., Manhattan Project Rept. CH-946, 1943: revision to appear in 

 HoUaender, A., Radiation Biology, Vol. 1, McGraw-Hill. 



