ILSE LASNITZKI 



of the radiation effect on cells exposed in the fresh and frozen state expressed 

 as the difference in percentage take from their respective controls. The 

 upper line gives the difference of tumours deriv^ed from frozen, the lower 

 line that obtained from fresh cells. Taking the results at 3 and 4 weeks 

 following grafting, the effectiveness of radiation is increased for the frozen 

 cells by a factor of two. 



The greater effectiveness of radiation on frozen cells is further borne out 

 by measurements of tumour sizes. Figure 5 gives the tumour volume in mm^ 

 for irradiated frozen and fresh grafts. Four weeks following inoculation 



lOaOr 



mTTi? 



Figure 5. Tumour volume in mm' obtained from 

 irradiated {gamma rays) fresh and frozen grafts 



2 3 



Time in weeks 



tumours derived from fresh cells have reached a size of 1,000 mm^ as against 

 170mm^ for those obtained from frozen cells. 



Cell counts made in the growing edge of established tumours show that 

 the mitotic rate is similar whether the tumours are derived from fresh or 

 frozen irradiated cells but that the proportion of abnormal meta- and ana- 

 phases is increased in tumours obtained from frozen grafts. Figure 6 

 illustrates the results of cell counts made on tumours four weeks after implan- 

 tation. The two columns on the left represent mitosis as a percentage of 



76 

 % 



12 



I 



J. 







I 





I 



: 



Figure 6. Mitosis expressed as percentage of resting cells 



[left-hand columns) and abnormal meta- and ana-phases 



expressed as the percentage of total mitosis [right-hand 



columns) 



resting cells. It is 6 per cent of resting cells for tumours derived from 

 irradiated fresh cells, and 7 • 2 per cent for tumours derived from irradiated 

 frozen cells. The two columns on the right give the proportion of abnormal 

 meta- and ana-phases as a percentage of the total mitotic count. The 

 figures are : 5 per cent for fresh and 15-3 per cent for frozen tumours. It 

 is reasonable to assume that some of these abnormalities do not produce 

 viable daughter cells and that this loss in viability may, at least partly, be 

 responsible for the slower growth rate in spite of an equal mitotic index. 



The greater effectiveness of radiation in the case of frozen tumours was 

 rather contrary to expectation. Exposure, in these experiments, took place 

 on the bench immediately after the removal of the frozen tumour from the 



323 



