218 L. F. LAMERTON 



relatively long line of precursors would both tend to delay the onset of cell 

 repopulation. 



Also one must recognize the possible importance of generalized tissue 

 dose. In the bone-marrow, capillary changes and haemorrhage might lead to 

 a collapse of cell proliferation at a dose-rate lower than the limiting value for 

 individual cell function, whereas the gut architecture might be of a less 

 susceptible type. 



ACKNOWLEDGMENTS 



This paper is a short summary of work carried out by a number of 

 investigators in this Department and I would like to express my appreciation 

 particularly to Miss K. Adams, Dr. J. P. M. Bensted, Mr. J. Blackmore, 

 Dr. N. M. Blackett, Mr. B. I. Lord and Mrs. Doris Wimber and to Professor 

 W. V. Mayneord, Director of the Physics Department, Institute of Cancer 

 Research, Royal Cancer Hospital. 



REFERENCES 



Bloom, M. A. (1950). Radiology 55, 104. 



Kember, N. F., Qitastler, H., and WniBER, D. E. (1962). Brit. J. Radiol. 35, 290. 



Lamerton, L. F., Pontifex, A. H., Blackett, N. M., and Adams, K. (1960). Brit. J. 



Radiol. 33, 287. 

 Lamerton, L. F., Steel, G. G., and Wimber, D. R. (1961). "Fundamental Aspects of 



Radiosensitivity", p. 158. Brookhaven Symposia in Biology, no. 14. 

 Lamerton, L. F., Lord, B, I., and Quastler, H. (1962). 5th Int. Symposium on 



Radioactive Isotopes in Clinical Medicine and Research, Bad Gastem, 1962. 



StraJilentherapie (in press). 

 Quastler, H., Bensted, J. P. M., Lamerton, L. F., and Simpson, S. M. (1959). Brit. J. 



Radiol. 32, 501. 



DISCUSSION 



CURTIS: This is a most interesting and a very puzzling finding — the ability of an animal 

 to withstand a much, much larger dose of radiation if it is given over a period of time than 

 if it is given instantaneously; and the concept which Prof. Lamerton has presented, of a 

 tissue which is dividmg very rapidly being able to withstand a lot more continuous 

 radiation because it can, so to speak, wipe the slate clean at the time of cell division and 

 then start aU over again. This is an interesting concept and I thmk that Dr. Sparrow 

 and his group at our laboratory have got a very considerable confirmation of this 

 concept from work with plants in which it is possible, by varying conditions such as 

 temperature and nutrient and things of this kind, to alter the rate of cell division and not 

 to alter much of anything else. In that case there is a very nice substantiation of this 

 concept that a plant can withstand chronic radiation almost in direct proportion to the 

 rate at which ceU division takes place. 



