Radiation and Ascites Tumour Metabolism 215 



been incorporated into DNA and RNA. ^*C-labelled cells 

 were X-ray-killed and mixed in various proportions with 

 imlabelled living cells, and mice were inoculated with these 

 mixtures. Analyses made on the fifth day after inoculation, 

 when control experiments showed that all X-ray-killed cells 

 were completely lysed, showed consistently high incorporation 

 of activity into the living cells, e.g. when a mixture with a 

 ratio of living : dead cells =1:1 was used, about 40 per cent 

 of the activity was incorporated into the living cells, and the 

 activitv was found to be distributed between DNA and RNA 

 in the same proportions as in the inoculated sample. 



This transfer of activity and, thus, of metabolites from dead 

 to living cells is not unexpected but, nevertheless, it does not 

 seem to have received much consideration in radiobiological 

 work. The extent to which, and in particular, how soon after 

 administration of the dose such a transfer takes place, is still 

 uncertain. It would seem, however, that in studies with labelled 

 compounds, carried out several days after administration of 

 an LD50 dose, such secondary reactions cannot be ruled out. 



In recent years, considerable work has been devoted to the 

 question of whether compounds like DNA, RNA and proteins 

 are metabolically stable and do not undergo concentration 

 changes during cell division and growth. Several observations 

 indicate that DNA from unicellular organisms is equally dis- 

 tributed between the daughter cells by mitosis without 

 previous degradation and that no replacement occurs in the 

 resting cells; this seems to be the case e.g. in bacteria (Her- 

 shey, 1954). In higher organisms the stability of DNA is 

 more controversial (Hevesy, 1948; Stevens, Daoust and 

 Leblond, 1953; Barnum, Huseby and Vermund, 1953), but 

 the evidence of some investigators favours this concept 

 (Barton, 1954; Fujisawa and Sibatani, 1954). The stability 

 of RNA as well as of DNA was advocated by Nygaard 

 (Nygaard and Rusch, 1955) from experiments on regenerating 

 liver. The proteins of ^-galactosidase from Esch. coli were 

 found by Hogness, Cohn and Monod (1955) to be static. 

 Evidence to the contrary has been put forward even in the 



