RADIOACTIVE TRACERS 



871 



When Ehrlich tumour cells irradiated in vitro were inoculated into 

 mice and the cell multiplication was assayed, results were obtained by 

 FoRSSBERG (1956) 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. Forssberg emphasised the importance 

 of transfer of metabolites from dead to living cells. While these and 

 possibly also humoral substances promote DNA formation, exposure to 

 radiation exerts a contrary effect. Twelve hours after exposure of mice 



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 "o 



o 



QJ 



c 



> A 



o 



u 

 □ 2 



u 



Q. 



5 10 15 



Aqe of tumor transplants in days 



20 



Fig. 13. The relationship between age of tumour and specific 

 activity of liver desoxypentosenucleic acid in mice bearing mammary 



carcinomas. 



to 1040 r the specific activity of the liver DNA phosphorus of mice 

 injected with embryo mash was found by Kelley and Jones (1953) 

 to be 0.29 while that of non-injected animals was only 0.19. 



The early observation that while irradiating a flank of the tumour 

 bearing rat the incorporation of ^^p into DNA of a second protected 

 tumour present in the other flank of the rat was depressed as well is 

 presumably to be explained in a similar way (Ahlstrom, Euler and 

 Hevesy, 1947; Holmes, 1949). 



From the above results it follows that presence of a tumour, even if 

 metastases are absent, promotes growth of some organs. 



The facts which I have had the privilege to communicate were to some 

 extent intermingled with hypotheses. A hypothesis, as the late Sir J.J. 

 Thompson remarked, is not a creed but a policy. How far the hypotheses 

 mentioned will, if only on a very modest scale, prove to be useful in 

 promoting the understanding of pathochemical changes produced by 

 radiation the future has to reveal. 



In November 1897, Silvanus Thompson delivered the first Presi- 

 dential Address to the Roentgen Society. It was devoted to the study 



