Radiation and Ascites Tumour Metabolism 213 



first two hours following irradiation, and renewed cell division 

 which appears at 20 hours must be preceded by a period of 

 preparation well before that time. 



Determinations of DNA, calculated per single cell, indicated 

 a slight increase only during the 48-hour postirradiation 

 period, whereas total N and RNA increased considerably. 

 Almost as a consequence of the rather unimpaired synthesis 

 of the cellular constituents (with the exception of DNA), the 

 average cell volume also showed a progressive increase. It is 

 interesting to compare the rate of cellular enlargement and 

 synthesis of N and RNA of the irradiated cells with the rate of 

 cell multiplication in the non-irradiated tumour. It appears 

 that all these measures are the same within the hmits of 

 error of determination. In other words, this impUes that the 

 production of cell mass in an irradiated sample occurs through 

 an increase in the mass of single cells while in the non- 

 irradiated population the cell mass production during the 

 same period is due to division, producing cells of ordinary size. 



A survey of the current literature reveals a number of 

 difficulties with regard to the quantitative interpretation of 

 radiation effects when doses of the order of LD50 are given. 

 An example of this is provided by growth rate studies on Ehrl- 

 ich ascites cells irradiated in vitro : when mice were inoculated 

 with the irradiated cells and the cell multiplication assayed 

 (Revesz, 1955), results were obtained which suggested that 

 decay products from X-ray-killed and lysed cells may serve 

 the survivors as an additional substrate, thus enhancing the 

 growth rate. Furthermore, growth rate studies of artificial 

 mixtures of X-ray-killed and living cells gave similar results. 

 To arrive at more precise information on the effects of lethal 

 doses in the present case, model experiments were designed 

 and preliminary results may be mentioned here. The stimula- 

 tion to enhanced growth at certain dose levels could be due to 

 a general increase in the pool of metabolites, arising from the 

 disintegration of dead cells; alternatively some particular pro- 

 ducts may be more effective in this respect. For several reasons, 

 nucleic acids are the most interesting in this connection. 



