588 



ADVENTURES IN RADIOISOTOPE RESEARCH 



of fresh blood placed in the cuvette absorbs much of the radiation of 

 the sample. An activity five times as large is registered when measuring 

 the activity of 100 mgm of dry blood as in the measurement of 1.5 ml 

 of fresh blood placed in Zerahn's cuvette. 



EXPERIMENTAL RESULTS 



Figures 1, 2 and 3 demonstrate the change in the ThB content (activity) 

 of the circulating blood with time. The third case investigated was one 

 of polycythemia, in which the mixing of the injected and the circulating 

 blood was probably slower than usual, as the maximum activity of the 

 blood was reached after only five minutes. Figures 4, 5, 6 and 7 demon- 

 strate the results of blood volume determinations carried out by using 

 first ThB-labelled erythrocytes, then ^^P-labelled red corpuscles. 



When we carried out the experiments, the result of which is shown 

 by Figures 1 to 7, we were not yet cognizant of the beneficial effect of 

 a 30-minute incubation of the active blood previous to its injection. 

 Nevertheless, the ThB label was found to be better preserved than 

 the ^^P label. Results of the experiment in which blood incubated for 

 30 minutes was injected, are seen in Table 2. 



Table 2. — Change in the ThB Content of Circulating Blood with Time 



Time between 



injection and 



sampling in 



minutes 



3 



5 



15 



30 



60 



Standard 

 sample 



Activity of dry samples secured 



from human subjects (Counts per 



minute) 



Relative activities 



100 



99.7 

 100.3 

 104 



98.4 



513 



In this experiment, in the course of 57 minutes, the ThB loss by the 



circulating blood was found to be —3.0 per cent, +4.3 per cent, -|-0.4 per 



cent, and 1.5 per cent, respectively, which compares with a loss of about 



+6 per cent in the case of ^^P-labelled red corpuscles. In the course of 



24 hours, one-third to one-fourth of the ThB content of the red cells is 



given off, which compares with a 50 per cent loss of ^-P by the labelled 

 erythrocytes.*^7) 



