902 ADVENTURES IN RADIOISOTOPE RESEARCH 



ascribed to nucleic acid phosphorus. The experiments were carried out 

 with seedlings grown in a labelled nutrient solution. The specific activity 

 of the total P being in such a case identical with the specific activity of 

 the nucleic acid P, we can calculate from the specific activity of the 

 nucleic acid exuded into the solution in which the seedling is placed, 

 and from the specific activity of the total P of the seedling (cf. p. 903) 

 the amount of nucleic acid exuded. The application of the technique of 

 parted roots is clearly not advisable when determining the amount of 

 labelled nucleic acid exuded into the nutrient solution or distilled water. 



As, simultaneously with the exudation of labelled nucleic acid into the 

 nutrient solution, a passage of labelled phosphate takes place, it is 

 necessary to purify the radioactive nucleic acid from the radioactive-free 

 phosphate. This was obtained in the following way. To an aliquot (25 cm^) 

 of distilled water, in which a wheat seedling was placed for 1 hour, we 

 added 100 mgm of inactive ribosenucleic acid, simultaneously adding 

 0.2 cm^ 1 N NaOH.Then, for each cm^ solution, 0.44 cm^ saturated NaCl, 

 0.025 cm^ 1/2-mol. NagHPO^, and 0.087 cm^ i^-mol- CaClg were added. 

 The amounts of the ingredients to be used were kindly suggested to the 

 author by Professor Einar Hammersten. Subsequently, the calcium 

 phosphate precipitate was removed by centrifuging the solution. The 

 liquid obtained was poured into 5 times its weight of glacial acid. 16.4 

 mgm were secured, showing an activityof 2.8activity units or 0.17 units 

 per mgm. 



Control experiments described below made it clear that such a proce- 

 dure is effective in removing active phosphate from the nucleic acid; 

 the same was the case when the nucleic acid precipitate was redissolved 

 and reprecipitated by an alcoholic solution of hydrochloric acid. From 

 the fact that, within the errors of experiment, the activity of the nucleic 

 acid fraction did not change when it was reprecipitated we can conclude 

 that it did not contain adhering active phosphate. The activityof 1 mgm 

 nucleic acid was found to be 1.7 and 1.6 activity units, respectively, 

 before and after reprecipitation. 



The control experiments were carried out in the following way. 50 mgm 

 inactive ribosenucleic acid was dissolved, 250,000 activity units were 

 added and NaOH, NaCl, NagPHO^ and CaClg were added as well. The acti- 

 vity of the 5.3 mgm nucleic acid secured as described above was less than 

 10~^ part of the activity added, showing that the separation of free 

 phosphate from the nucleic acid was very effective. 



We may expect the active nucleic acid present in the solution and the 

 inactive nucleic acid added to follow each other during the separation 

 process and, as we recovered only 16.4 p. c. of the inactive nucleic acid 

 added (100 mgm) in the experiment described above, we can expect a 

 •corresponding fraction of the active nucleic acid to have been recovered 

 as well. We have thus to multiply the 2.8 activity units with 6.1 to 



