STUDIES UPON SOME ISOGENIC CHIMAERAS 337 



number of cells injected after irradiation are shown. Clearly, the more cells 

 injected the more rapidly and effectively are nearly all components of the 

 peripheral blood restored to near normal values. Further, injection of 10'^ 

 ceUs appear to have a disproportionately large effect in comparison with 

 injection of 10^ cells. From this it is temptmg to suppose that the period at 

 risk after radiation is reduced by rapid restoration of one or all components of 

 the peripheral blood and that injection of 10' cells is most effective in reduc- 

 ing the period at risk. 



It might also be supposed that the period at risk woidd generally be 

 inversely proportional to the number of cells injected. From which it follows 

 that, irrespective of percentage mortality, the mean time of death might be 

 later after injection of a small number than after a large number of cells. 

 Evidence at hand, though as yet numerically inadequate, gives no support to 

 this corollary. 



ACKNOWLEDGMENTS 



This work has been supported by a grant from the International Atomic 

 Energy Agency and also by grants to the Chester Beatty Research Institute 

 (Institute of Cancer Research: Royal Cancer Hospital) from the Medical 

 Research Council, the British Empire Cancer Campaign, the Anna Fuller 

 Fund, and the National Cancer Institute of the National Institute of Health, 

 U.S. Public Health Service. 



REFERENCES 



KoLLEE, P. C, Davies, A. J. S., and Doak, S. M. A. (1961). Advanc. Cancer Res. 6, 181. 

 LiNDSLEY, D. L., Odell, T. T., and Tausche, F. G. (1955). Proc. Soc. exp. Biol. N.Y. 



90, 512. 

 Lorenz, E., Uphoff, D. E., Reid, T. R., and Shelton, E. (1952). J. nat. Cancer Inst. 12, 



197. 



DISCUSSION 



MOLE: If with 25,000-1,000,000 donor cells you can send up the survival from to 80% 



and then you have to give 10 million cells to increase survival from 80 to 100%, the 



observation would indicate that there must be an obvious difference in the way the 



animals die which received a low or high number of cells. Is there a difference in the time 



of death? 



koller: We found no difference in the way the animals die after the various number of 



donor cells injected. 



lajvierton: Professor Koller gives his figures as percentages of controls. Now if your 



control values remain fairly steady this is aU right but in oiu* rats, for instance, we have 



found a very considerable variation. We suspect seasonally, or from year to year, we do 



