986 



ADVENTURES IN RADIOISOTOPE RESEARCH 



day is still present in the circulation at any later date. The percentage 

 share of the erythrocytes formed during the first day of the experiment 

 in the total red corpuscle content of the circulation at different dates 

 is shown in Fig. 6. 



One may be tempted to explain the results obtained by assuming a 

 successive loss of the deoxyribonucleic acid content of red corpuscles 

 during their life-cycle. However, an investigation of the deoxyribonucleic 

 acid content of individual erythrocytes by Ris and Mirsky(4^) has shown 

 that this value for each red corpuscle is constant within 10%. 



Fig. 7. Life-cycle of the red corpuscles of two hens. Abscissae: 



days after start of experiment; ordinates: specific activity of de- 

 oxyribonucleic acid phosphorus extracted from the corpuscles secured 

 at different dates (reproduced, with permission, from Nature 156, 



534 (1945). 



As to a possible objection that not the inorganic but an organic P 

 fraction of the bone marrow is the pertinent precursor of deoxyribonucleic 

 acid, Ottesen has shown that the existence of a deoxyribonucleic acid 

 precursor of considerably lower turnover rate than that of the inorganic 

 P of the marrow is incompatible with the results demonstrated in Fig. 6. 

 A precursor of more rapid turnover rate than that of the marrow inorganic 

 P would clearly not influence the results obtained. 



A method very similar to that described above had been used by 

 Shemin and Kitten berg^^^) in the determination of the life-cycle of 

 human red corpuscles. They administered glycine containing i^N to 

 human subjects and followed the change with time of the i^N content 

 of haemin isolated from the erythrocytes. They found this content to 

 decline rapidly after the lapse of 109 — 127 days. Ottesen based his con- 

 siderations on the ratio of the ^ap content of deoxyribonucleic acid P 

 and its precursor (inorganic P), but Shemin and Rittenberg could not 



(4^) J. Gen. Physiol. 33, 125 (1939). 

 (") J. Biol. Chem. 166, 627 (1946). 



