RADIOACTIVE INDICATORS IX BIOCHEMISTRY 



975 



formed afterwards. The old molecules are not radioactive, but the new 

 ones contain ^^P. 



Let us assume that out of 100 deoxyribonucleic acid molecules present 

 in the non-irradiated tumour two arc found to contain ^^p two hours 

 after administration of labelled phosphate while in the irradiated tumour, 

 in which deoxyribonucleic acid formation is suppressed, the correspond- 

 ing figure is only 1. Such a difference is readily ascertained. In the first 

 case, the Geiger counter or another suitable measuring instrument will 

 indicate an activity of, say, 200 counts per minute, in the second case 

 only 100. Radioactive measurements can very easily be made, a fact 

 which contributes materially to the wide application of the method of 

 radioactive indicators. 



In Table 6 the effect of irradiation with X-ray doses ranging from 

 335 to 1500 r. on the Jensen- sarcoma of the rat is shown^^"""). A few minutes 

 after the irradiation, labelled sodium phosphate was injected into 68 

 rats and into the same number of controls. The effect of irradiation on 

 the formation of deoxyribonucleic acid molecules is seen to be most 

 effective shortly after irradiation. 



Table 6. — Effect of X-rays on the Formation of Labelled 

 Dkoxyribonucleic Acid after Administration of Labelled 



Sodium Phosphate 



Dose, in r units 



Duration of experiment, 

 hours 



Ratio of labelled nucleic acid 



formation in non-irradiated and 



irradiated sarcoma 



750— LjOO 

 350—1500 

 650—1500 



3.2 

 2.4 

 2.2 



In another set of experiments^^!) with 32 rats the mean ratio of the 

 labelled nucleic acid formation in the non-irradiated and irradiated rats 

 after the lapse of 2 hours was found to be 2.05, and in a third set^^^) (40 

 animals) 2.2. Similar results were obtained by Barbara Holmes^^^*), 

 who, injecting labelled phosphate into 14 rats, found a mean value of 

 2.1 for the above ratio 1/0 — 2 hours after irradiation with 2000 r. 



In organs such as liver, kidney, spleen, and intestinal mucosa, the 

 formation of deoxyribonucleic acid formation was found to be reduced 



(3oa)yQjj EuLER and Hevesy, Arkiv Kemil7, A Nr. 30 (1944); Hevesy, Bev. 

 Mod. Plnjsics 17, 102 (1950). 



(31) Von Euler and Hevesy, X^Z. Danske Videnskab, Selsk. Biol. Medd. 17, 

 Nr. 8 (1942). 



(32) Ahlstrom, v. Euler and Hevesy, Arkiv Kemi 19, A Nr. 13 (1945). 



(33) Brit. Bad. J. 20, 45 (1947); 22, 487 (1949). 



