ILSE LASNITZKI 



fresh control and irradiated grafts following a dose of l,500r of X-rays. 

 The reduction is of the same order as in the gamma ray experiment : it is 

 42 per cent at two weeks and 46 per cent at four weeks following implanta- 

 tion. Figure 9 gives the results obtained with frozen control and irradiated 

 cells. The take is 13 per cent at two weeks, and 18 per cent at four weeks 

 after grafting. Figure 10 gives a direct comparison of the radiation effect 

 expressed again as the difference in percentage take from that of the controls. 

 Taking the points at three and four weeks the radiation effect for frozen 

 tumour is here again increased by a factor of approximately two. 



The second experiment thus confirms the results obtained with the gamma 

 ray and shows that the rise in temperature cannot have been responsible 

 for the increased radiation effect on frozen cells. The greater effectiveness 

 of radiation on frozen tumour cells seems, at this stage at least, difficult to 

 interpret. According to current views (Craigie^), freezing involves a certain 

 degree of cytoplasmic dehydration. The ensuing intracellular increase in 

 salt concentration may render the cells more vulnerable to ionizing radia- 

 tions although it may not impair cell survival under normal conditions. 

 Another alternative, suggested tentatively, is that at the temperature pre- 

 vailing during exposure the movement of free radicals and ions produced 

 by radiation may be restricted more for one species than for another : in 

 this case less recombination would occur and more free radicals remain 

 available for interaction with biological structures which under the con- 

 ditions of the experiments return to normal temperature and activity shortly 

 after exposure. 



It is hoped to throw more light on this matter by further experiments in 

 which thawing and reinoculation after irradiation will be delayed, 



REFERENCES 



1 Glucksmann, a. and Spear, F. G. Brit. J. Radiol. 1939, 12 486. 



2 Goldfeder, Anna. Radiology, 1951, 57 845. 



3 Lasnitzki, Ilse. Brit. J. Radiol. 1953, 27 228. 



* W.A.RBURG, Otto and Hiepler, E. Z- Maturforsch, 1952, 7b 3, 193. 



5 Craigie, J. Advances in Cancer Research, 197, New York, Academic Press, 1954. 



325 



