NUCLEIC ACID IN THE ORGANS OF THE RAT G65 



of the activity of the standard preparation, we find U.OUl pei' cent of the labelled 

 P administered to be present in 1 mgm nucleic acid P. 



The weight of the male adult albino rats used varied between 250 and 320 gm. 

 They were kept in a normal diet. The labelled phosphate administered by subcu- 

 taneous injection had an activity corresponding to '.i //Curie. 



CONTROL OF THE EFFECTIVITY OF THE PURIFICATION PROCESS 



To a crude nucleic acid fraction containing 200 mgm nucleic a(;id we added 

 75,000 relative units of radioactive phosphorus (^^p). Each time, decreasing amounts 

 of inactive ammonium phosphate were added to the filtrate containing the nucleic 

 acid. The amount of (NH^)2HP0^ added varied between 100 and 30 mgm. After 

 successive purifications, the following activity figiires were obtained for the nucleic 

 acid. 



Xumber of Activity of 



purifications fractions 



The nucleic acid purified 3 times thus contained but 1/8000 part of the labelled 

 phosphate added. 



The successive purification of nucleic acid P from other than free P can be 

 controlled in the following way. The specific activity of an ahquot of the nucleic 

 acid P of the purified sample is determined. Another aliquot of the sample is dissol- 

 ved subsequently and is re-precipitated as described above, but, without adding 

 phosphate. The specific activity of the P of the precipitate obtained is then again 

 determined. If no other phosphorus than nucleic acid P is present in the sample 

 the specific activities determined should be identical. When controUing the purity- 

 of nucleic acid extracted from the liver and purified twice in the manner described 

 above, a further purification reduced the specific activity of the phosphorus obtained 

 from the nucleic acid by 5.5 per cent. 



Furthermore, we investigated whether the nucleic acid obtained is 

 exclusively of desoxyribose type or contains also some nucleic acid oi' 

 the ribose nucleic acid type. 



To 7.6 mgm active thymus nucleic acid dissolved in 1.0 cc. 7io N. NaOH 

 about 60 mgm yeast nucleic acid, dissolved in 2 cc. 7io N- NaOH were 

 added. After precipitating but once, the nucleic acid, as described on 

 p. 664, we redetermined the specific activity of the nucleic acid P. 

 This was found to be 76 per cent of the specific activity of the value 

 measured at the start of the experiment. A single precipitation sufficed 

 thus to remove 96 per cent of the yeast nucleic acid added. 



