592 



ADVENTURES IN RADIOISOTOPE RESEARCH 



wish to avoid this restricted activity, we can replace the active plasma 

 by inactive plasma, and inject the blood sample, the activity of which 

 is now exclusively located in the erythrocytes. We can, however, reach 

 almost the same result by incubating the active blood for about 20 

 minutes at 37° C. The percentage of ThB still present in the plasma after 

 incubation is seen in Table 3. The ThB content of the plasma can be 

 strongly reduced by incubating the blood for 20 minutes, as seen in 

 Table 3. 



Table 4. — Loss of ThB by Injected Active 



Plasma (2 X 10^ Counts Injected. Plasma and 



CoBPixscLE Content of the Httman Subject = 3020 



gm AND 1990 gm Respectively) 



Time in minutes 

 after injection 



Per cent ThB still 



present in the 

 circulating plasma 



Per cent ThB located 



in the circulating 



red corpuscles 



In incubating active corpuscles with inactive plasma in vitro for 

 1 hour, 1 to 2 per cent of the ThB of the corpuscles enter the plasma 

 phase. 



Loss of ThB by Injected Active Plasma 



ThB present in the injected plasma is lost at a remarkable rate, as 

 shown by the data of Table 4 and in Figure 8. Part of lost ThB pene- 

 trates the capillary wall, and part intrudes into the blood corpuscles. 



In some of our experiments, we found the percentage incorporation 

 of the injected plasma ThB in the circulating erythrocytes after the 

 lapse of 3, 60 and 360 minutes, respectively, to be as high as 25, 40 and 45. 

 These figures compare with 1, 5 and 9 for ^sp infusion into the red cor- 

 puscles following injection of ^sp-labelled plasma*^^\ 



Summary 



1. Thorium B (ThB) is a disintegration product of the radioactive gas thoron. 

 The procedure for preparation of ThB is described. 



2. The advantages of ThB for blood volume determinations are that it accumu- 

 lates to 99 per cent in red corpuscles, is released more slowly than radiophosphorus 

 (loss less than 4 per cent in one hour) and has a half-time of 10.6 hours, which 

 permits repeated determinations of blood volume. The radiation emitted by ThB 

 is measured as easily as that of radioactive phosphoinis. 



