90 p. L. T. ILBERY, P. A. MOORE, S. M. WINN, AND C. E. FORD 



as judged by abnormal cbromosome complement, in general did not take. It 

 was thought unlikely that the failure to transplant was due to insufficient 

 numbers of pre-leukaemic cells in the innoculum or to non-isotopic placement 

 of cells as a very few established leukaemic cells will take when placed sub- 

 cutaneously, intraperitoneally, or intravenously. Kather, as a working 

 hypothesis, the inference was drawn that in this model, cells with altered 

 karyotypes were present before the supervention of malignancy as judged by 

 the inability of the changed cells to transplant. 



ACKNOWLEDGMENTS 



The investigation has been supported by a grant to the Department of 

 Preventive Medicine, University of Sydney, from the New South Wales State 

 Cancer Council and from an anonymous donor. 



REFERENCES 



BovERi, T. (1929). "The Origin of Malignant Tumours". Williams and Wilkins Co., 



Baltimore. 

 Carter, T. C, Lyon, M. F., and Phillips, R. J. S. (1955). J. Genet. 53, 154. 

 Ford, C. E., and Hammerton, J. L. (1956). Stain Technol. 31, 247. 

 Ford, C. E., Hamerton, J. L., and Mole, R. H. (1958). J. cell comp. Physiol. 52, 235. 

 Ford, C. E., Ilbery, P. L. T., and Loutit, J. F. (1957). J. cell. comp. Physiol. 50, 109, 



Suppl. 1. 

 FuRTH, J. and YoKORO, K. (1960). ''Proc. 3rd Asian Conf. EadiobioV\ (P. L. T. Ilbery, 



ed.) 2, 86. 

 Ilbery, P. L. T. (1960). Aust. J. exp. Biol. 38, 69. 

 I"Laplan, H. S. (1959). Ciba Foundation Symposium on Carcinogenesis, Mechanisms of 



Action. (G. E. W. Wolstenholme and M. O'Connor, eds.), p. 233. 

 Nagareda, C. S., and Kaplan, H. S. (1958). Proc. Amer. Ass. Cancer Res. 2, 330. 



DISCUSSION 



MOLE: Radiation produces chromosomal changes. How do you know that these cliromo- 

 somal changes have anything to do with the leukaemia that would have been expected 

 to develop if the animals had been left alone? 



ilbery: The number of animals exhibiting abnormalities of chromosome number and/or 

 form amongst the pre-leukaemias as shown in Table I represented observable cytogenetic 

 changes in twelve out of the nineteen thymuses examined. This incidence, perhaps 

 fortuitously, approximates the expected yield of radiation-induced leukaemia using our 

 schedule of y-irradiation in the C57BL strain and our C6 hybrids. In four thymuses there 

 was a mode of 41 chromosomes present and in another 5, sub-modes of greater than 40 

 chromosomes — strong presumptive evidence of malignancy as I have not observed such 

 numbers of cells containing more than the normal complement except in malignant 

 tissues. 



