NUCLEIC ACID IX SARCOMA SLICES 781 



at 20°, the determination of nucleic acid was performed similarly. The 

 method of "isotopic dilution" was applied to this determination. 



After 40 niin boiling of the purified tissue (5 gm) with 5% sodium 

 hydroxide solution, 10 mgm of radioactive nucleic acid was added to the 

 sample and the nucleic acid was isolated after repeated purification. Tho 

 nucleic acid content of Ihe tissue sample can be calculated from the 

 specific activities of the added and isolated nucleic acid and from the 

 amount of nucleic acid added. 



The added amount of nucleic acid had an activity of 461 pulses/min 

 per mgm P, while the corresponding value for the isolated nucleic acid 

 amounted to 28.2; 9.9 mgm of active nucleic acid had been added. The 

 required content of nucleic acid in the purified sarcoma tissue (5 gm) 

 therefore amounts to: 



X = 9.9 (461/28.2 — 1) = 152 



or 30.4 mgm of nucleic acid per gm of sarcoma tissue. 

 The analysis of the sample which had been kept for 24 hr yielded: 



X ^ 10.0(1641/36.0 — 1) = 118 



or 23.6 mgm of nucleic acid per gm of sarcoma tissue. 



Only about one-quarter of the nucleic acid content was therefore 

 decomposed during the 24 hr storage. 



The data themselves (but not , on the contrary, the ratio) need 

 to be treated with great caution. The use of the isotope dilution method 

 assumes, of course, that the added radioactive sample behaves in all 

 respects like the nucleic acid originally existing in the prepared sub- 

 stance. Now the degree of polymerization of the multiply purified 

 (a treatment which cannot be relinquished) nucleic acid may differ 

 considerably from the degree of polymerization of the nucleic acid 

 present in the crude alkaline extract, and it is conceivable that in the 

 purification of the preparation a greater or smaller fraction of the added 

 radioactive nucleic acid than of that originally present enters into the 

 individual precipitations. 



Growing sarcomas weighing 10 to 17 gm from rats weighing from 106 

 to 113 gm were used in the experiments which have been described. The 

 radioactive nucleic acid was obtained from the sarcomas of such animals 

 which had been injected 2 days previously with radioactive sodium 

 phosphate. 



DISCUSSION 



The following values have been obtained for the percentage ratio of 

 1 mgm nucleic acid P to 1 mgm free sarcoma P: 



