988 ADVENTURES IN RADIOISOTOPE RESEARCH 



sodium phosphate into the hen, the specific activity of the plasma inor- 

 ganic P was kept at a fairly constant level. As demonstrated by Fig. 7, 

 after the lapse of 33 days the specific activity of deoxyribonucleic acid 

 no longer increased, indicating that only red corpuscles foimed during 

 the experiment were now present in the circulation. As significant 

 amounts of labelled red corpuscles were observed only 4 days after the 

 start of these experiment, the life-span of the erythrocytes works out 

 again to be 29 days. 



(b) Life-time of Human White Corpuscles 



The same considerations as described above were applied by Ottesen 

 in the determination of the life-time of human lymphocytes and granulo- 

 cytes. His results are illustrated by Figs. 8, 9, and 10. In these expe- 

 riments, not the specific activity of inorganic P of the blood plasma but 

 the corresponding value of the urine inorganic P was determined, as 

 well as the specific activity of deoxyribonucleic acid P of lymphocytes 

 and granulocytes. As with nucleated erythrocytes, the deoxyribonucleic 

 acid molecules present in the white corpuscles were found to remain un- 

 changed during the life-time of the corpuscles, all turnover being absent. 

 Correspondingly, the ratio of the labelled deoxyribonucleic acid content 

 of the white corpuscles formed during the first day to that of the totality 

 of circulating white corpuscles is identical with the ratio of the number 

 of white corpuscles formed within the first day to the total number of 

 white corpuscles present in the circulation. It requires a few days before 

 the white corpuscles are formed and released into the circulation. Owing 

 to this, the labelled granulocyte content of the circulation first increases 

 and reaches a maximum after the lapse of 6 days. About 14% of the 

 granulocytes then present are such as were formed during the first day. 

 Their number decreases, however, fairly rapidly with time. After a 

 further 4 days their proportion is reduced from 14 to 7%. 



A closer investigation of the number of lymphocytes formed during 

 the first day, and still present in the circulation, revealed that an appreci- 

 able part of lymphocytes present is formed many months before the 

 start of the experiment; thus lymphocytes contain an appreciable pro- 

 portion of cells of long life. This conclusion is based on the figures obtained 

 for the ratio of the specific activities of plasma (urine) inorganic P and 

 the corresponding value of deoxyribonucleic acid P extracted from 

 lymphocytes. This ratio should be equal to or less than unity for all 

 lymphocytes formed during the experiment. A ratio appreciably higher 

 than unity was, however, found even after the lapse of more than a 

 m.onth. 



