704 ADVENTURES IN RADIOISOTOPE RESEARCH 



7000 r the activity of 1 mgm of nucleic acid phosphorus was found to be 

 equal to 0.1 per cent of the activity of 1 mgm of free liver phosphorus and 

 to 0.08 per cent of the activity of 1 mgm of free plasma phosphorus. The 

 experiments performed up to the present time with Ehrlich carcinomas 

 on mice have to some extent produced results differing from those 

 obtained with Jensen sarcomas, as will be shown in a future communi- 

 cation. 



By means of the possibility of measuring the effect exerted by X-rays 

 on the formation of nucleic acid molecules in a sarcoma with the aid 

 of radioactive indicators, their action on the sarcomas can be followed 

 chemically. It should be noted that the experiments described are easily 

 performed, preferably by comparing the activities of the nucleic acid 

 phosphorus in the sarcoma and of the free phosphorus in the sarcoma, 

 and also that it would be important to establish the effective dose of 

 X-rays causing a detectable reduction on the formation of radioactively 

 labelled nucleic acid. 



In the experiments described, the formation of radioactively labelled 

 nucleic acid was determined during the 2 hr following irradiation (the 

 irradiation itself lasted for at most 42 min). There is nothing to hinder 

 determination of the formation of radioactively labelled nucleic acid in 

 the first hour, the first half-hour or even shorter times after the irradia- 

 tion. It is thus possible to determine the chemical effect of X-rays on 

 the sarcoma immediately after irradiation. 



Phosphorus Content of Liver and Plasma 



The data in Tables 4—6 show that there is no essential difference 

 between the phosphorus contents of the plasma and liver in unirradiated, 

 slightly irradiated and more strongly irradiated animals (in all cases 

 only the sarcoma was irradiated). The average free phosphorus content 

 of the liver amounts to 51, 47 and 59 mgm %; the corresponding values 

 for the free phosphorus content in the plasma are 7.7,6.1 and 6.0 mgm %. 



Two hours after injection there is 1.04^^^ 2.05 and 2.00 per cent of 

 the injected ^^Pin 1 mgm of free liver phosphorus in unirradiated, slightly 

 irradiated and more strongly irradiated rats, respectively. The liver 

 therefore contains at this time (mean value of liver weight equals 7.1, 

 6.3 and 5.7 gm) about 7 per cent of the injected ^^P as free P. 



In 1 mgm of free plasma phosphorus 2 hr after injection there is 1.21, 

 1.83 and 1.72 per cent of the injected ^^P. Therefore 1 mgm of free liver 



1 In later experiments (see p. 706) 2.13 and 2.16 per cent of the injected ^^P 

 was found, respectively, in 1 mgm of free liver pliosphorus in unirradiated rats 

 and in animals irradiated with 2000 r. The corresponding values for the plasma 

 phosphorus were 1.21 and 1.15. 



