698 ADVENTURES I^^ RADIOISOTOPE RESEARCH 



solution centrifugecl and filtered, and the centrifuged residue was again 

 extracted with 2 cm^ of trichloroacetic acid and filtered. The whole of 

 the filtrate was diluted with water to 25 cm^; 2 cm^ of this was used for 

 colorimetric determination of the phosphorus by the Fiske— Subbarow— 

 Theorell method; 20 cm^ of the filtrate was treated with 80 mgm of disodium 

 hydrogen phosphate, and the whole of the phosphate was precipitated 

 as magnesium ammonium phosphate. After drying at 110° C this preci- 

 pitate was used for determination of the activity. 



The liver (usually 5 to 8 gm) was first treated for 15 min with 20 cm^ 

 of 25% trichloroacetic acid and for a second period of 10 min. The 

 trichloroacetic acid extract was filtered and the filtrate diluted with 

 water to 100 cm^. Phosphorus was determined colorimetrically in 1 cm^. 

 After addition of 80 mgm of sodium phosphate, 80 cm^ of the solution 

 was used for precipitation of the magnesium ammonium phosphate 

 required for the determination of the radioactivity. 



Irradiation of the Sarcoma 



The sarcomas were irradiated for periods of from 26 — 67 min with 

 X-rays emitted from a tube operated at 165 kV and 7 mA. A 0.5 mm 

 copper foil and 1 mm aluminium foil were used as radiation filters. The 

 irradiation was made at distances between 25 and 42 cm. Only the 

 sarcoma was irradiated; the other parts of the body of the rat were 

 protected against the action of the radiation by covering them with 

 lead plates. The NaC'l solution containing the radioactively labelled 

 sodium phosphate was injected 20 min after completion of the irradiation. 



The performance of experiments lasting for such a short time has the 

 advantage, among others, that the effect of the X-rays can be studied 

 soon after the ending of the irradiation. It is well known that in the 

 course of time considerable changes take place in irradiated tissue and 

 the effect of these changes on the nucleic acid metabolism can be studied 

 by injecting the radioactive one or more days and not immediately 

 after interruption of the irradiation. The results of such experiments w^ill 

 be discussed below. 



EXPERIMENTAL RESULTS 



The results of the experimental work can be seen in Tables 1—6. 

 Tables 1 — 3 contain data on the rate of formation of desoxyribo nucleic 

 acid in unirradiated and in slightly and more strongly irradiated sarcomas. 

 Tables 4—6 contain data on the fraction of injected ^^P which is to be 

 found after the passing of 2 hr in 1 mgm of free plasma phosphate phos- 

 phorus and in 1 mgm of free liver phosphate phosphorus. 



