Protein and Polynucleotide Turnover 205 



and 7 of the purines, and the ^^N content in adenine and 

 guanine are therefore used as a measure of nucleic acid turn- 

 over. On the incorporation into pyrimidines, on, the other 

 hand, httle is known. 



Concerning experimental conditions I will only mention 

 some facts that are necessary for the interpretation of the 

 results. Partial hepatectomy was performed on 20 to 40 rats 

 in each group. At different times after this operation isotopic 

 glycine was injected subcutaneously during the last eight 

 hours before the animals were sacrificed. The regeneration 

 times, viz. lifetime in hours after hepatectomy, were in our 

 experiments 11, 26, 32, 56 and 170. The only intentional 

 difference between these different groups is their stage of 

 regeneration. Each group received the same amount of isotope 

 during the same period before death. 



The regeneration was calculated from weighing the excised 

 and remaining parts of the liver in the usual way. The pooled 

 livers from each group were fractionated with a view to separa- 

 ting cell nuclei and cytoplasm. These tissue fractions were 

 mechanically disintegrated by vibrating with glass beads, and 

 were then extracted from lipids and after that from poly- 

 nucleotides. The remaining substance was treated with 

 trichloroacetic acid according to Schneider and after hydro- 

 lysis fractionated for amino-acids on starch and Dowex 50 

 columns. The polynucleotides were also degraded and the 

 nitrogenous bases separated on starch columns as adenine, 

 guanine, cytidine, uridine, thymine and cytosine. All 

 substances were analysed for purity. 



As to the conditions in the experiments on hens it may be 

 sufficient to say that in some cases the regeneration in the 

 bone marrow was stepped up considerably by destroying 

 about 50 per cent of the red blood corpuscles. [^^N] glycine 

 was used as precursor. The results will be given in the follow- 

 ing figures. 



When [^^N] glycine was used as a tracer precursor in more 

 or less rapidly regenerating bone marrow and non-regenerating 

 liver of the same hen, a correlation could be observed between 



