RADIOACTIVE IXDICATORS IN BIOCHEMISTRY 985 



inorganic P the specific activity of which corresponds to the mean value 

 of the inorganic P during that time intervaL This mean value, which 

 can be experimentally determined, is denoted by f{^). The contribution 

 of active deoxyribonucleic acid of red corpuscles formed during the first 

 day of the experiment to the total activity of erythrocyte deoxyribo- 

 nucleic acid measured after the lapse of 1 day is f{^) {0 ^), where is a 

 function of the time taken by the transition of the red corpuscles from 

 the marrow into the circulation, and also of the duration of the life- 

 cycle of the erythrocytes. Actually, we compare, not the deoxyribonucleic 

 acid activities of the total erythrocyte content of the circulation, but 

 the specific activities of deoxyribonucleic acid P fractions. 



The second day, the corpuscle deoxyribonucleic acid is formed liom 

 inorganic P having a much lower specific activity than the first day 



16 20 24 

 Time, days. 



Fig. 6. — Percentage of hen red corpuscles, formed during the first 

 day of the experiment, present in blood stream at the time indi- 

 cated on the a;-axis (Ottesen). 



the mean value of which is now /(l^). The contribution of active deoxy- 

 ribonucleic acid formed during the second day to the total deoxyril)o- 

 nucleic acid activity measured on the second claj'^ is now /(l^) (0^). 

 The share of the active deoxyribonucleic acid formed in the course of 

 the second day in the total activity of deoxyribonucleic acid of the red 

 corpuscles is somewhat different from the corresponding value during 

 the first day and amounts to /(}) (0^). 



In a similar way the contribution of the active deoxyribonucleic acid 

 formed during the third day to the total deoxyribonucleic acid activity 

 can be calculated and also the share of the deoxyribonucleic acid formed 

 in the course of the first and second day in the total activity measured 

 on the third day of the experiment can be determined. Each consecutive 

 day we find a new (0) value not represented previously. 



As the deoxyribonucleic acid molecules present in th(^ nucleated red 

 corpuscles were found to be entirely stable, not showing any perceptible 

 turnover, the above considerations permit one to determine what per- 

 centage, for example, of the labelled red corpuscles formed on the fiist 



