790 AD/ENTURBJ IN" RA.DIOI33raPE RE^BARCS 



Comment on papers 73 to 78 



In most of our experiments we exposed rats to irradiation and injected them 

 after exposure with ^^p.They were then killed at intervals of from 30 min to sever- 

 al days. In some of our experiments we irradiated injected animals that were 

 tied to a table throughout the experiment. Formation of labelled DNA was found 

 (Ahlstbom et al., 1944) to be much more strongly depressed in these experiments 

 than in the usual ones. It was, however, soon found (paper 73) that this interference 

 with DNA formation was not due to exposing the rats to uninterrupted irradiation, 

 but to circulation disturbances which prevented the radioactive indicator from 

 reaching the sarcoma. 



When the right flank of a rat having tumours both in the right and left flank 

 was irradiated, ^ap incorporation into ths DNA of the left flank was found to be 

 diminished as well (paper 74). This result induced experiments in which blood 

 of heavily exposed rabbits was transfused to sister rabbits (paper 75). The presence 

 of DNA formation blocking components in the circulation could not be determined 

 with certainty (paper 75). 



From Jensen-sarcoma prepared DNA was injected into the circulation of the 

 rat. After the lapse of 2 hr the total ^^p content of the plasma was reduced to 2 

 per cent of the amount of ^^p injected (paper 76). Marshak and Walker (1945) 

 observed that after the injection of ^^P labelled chromatin into the circulation of 

 partially hepatectomized rats, the Hver nuclei took up much more ^ap tban 

 when labelled phosphate was injected. We suggested the explanation that the 

 accumulation of ^^P in the liver nuclei after injection of labelled chromatin is 

 mostly or wholly due to the sphtting off of phosphate from the chromatin in the 

 liver, the phosphate being then incorporated into the liver nuclei. Our explanation 

 proved to be erroneous. Labelled DNA found appUcation in the study of sphtting 

 off phosphorus from the latter under the action of enzymes present in tissue extracts 

 (paper 78). 



The incorporation of ^^P into DNA of surviving sarcoma slices was also studied 

 (paper 77). In experiments taking 2 hr incorporation was 'found to make out 

 one-twentieth of the value observed in in vivo experiments. Addition of oestron, 

 diethylstilboestrol or caffein to the incubating fluid does not influence the rate 

 of labelled DNA formation, addition of cyanide, fluoride or monoiodoacetic acid 

 suppresses it. 



References 



A. Mahshak and A. C. Walker (1945) Amer. J. Physiol. 143, 235. 



L. Ahlstrom, H. Euler and G. Hevesy (1944) Ark. Ketni 18 B, 13 No. 13. 



