578 ADVENTURES IN RADIOISOTOPE RESEARCH 



If we wish to apply labelled red corpuscles as a clinical tool, it does 

 not suffice that the erythrocytes conserve their label during the deter- 

 mination to be carried out. It is of great importance as well that the 

 labelling process should not take more than some minutes, that the 

 radiation emitted by the labelled corpuscles is easily measurable and 

 that time consuming operations as separation of the erythrocytes from 

 plasma can be avoided. We found thorium B labelled red corpuscles to 

 respond to all these requirements. Thorium B labelled erythrocytes can 

 be prepared by leading a stream of oxygen containing thoron (thorium 

 emanation) through a blood sample for a few minutes only. A large part 

 of the thoron absorbed by the blood sample, as its half-life time amounts 

 to 55 seconds only, decays within the sample. As a result of this disinte- 

 gration radioactive ThB is formed which decays with a half time of 

 10.6 hr. Most of the ThB formed in the plasma is taken up by the red 

 corpuscles. Due to this fact and also to the very speedy disappearance 

 of ThB from the injected plasma the activity of the blood samples 

 secured after injecting ThB labelled blood into the circulation is almost 

 exclusively due to the activity of the red corpuscles. A separation of the 

 red corpuscles from the plasma in the secured blood samples can thus 

 be avoided. 



Within the first 2 hr loss of ThB by the labelled corpuscles is almost 

 negligible and for the coming hours restricted. While thorium B emits 

 soft /3-rays its daughter product thorium C with which it soon gets in 

 exchange equilibrium emits |S-rays of similar penetrability as does ^^P. 

 When measuring the radioactivity of thorium B labelled erythrocytes 

 we are thus mainly measuring the ^-radiation of thorium C. 



That the activity of thorium B -}- C decays with a half-time of 10.6 hr 

 has the advantage that the organism is exposed to radiation for a very 

 restricted time only after the radioactive isotope is introduced into the 

 circulation, less than 1/5 of the isotope being present after a lapse of 

 a day. 



A more detailed description of the above outlined method and the 

 results obtained by its application will be soon published. 



Summary 



Red corpuscles were labelled by adding ^^KCl to a blood sample kept at 37° C 

 for 2 hr. When reinjecting the blood sample to the patient in the course of 1 hr, 

 within the error of the blood volume determination which is 3%, no change in the 

 activity of the red corpuscles could be observed. 



Washed labelled red corpuscles injected into the circulation lost in the average 

 3.5% of their *^K. content in the course of the first hr, while the mean loss per 

 hr in the course of 24 hr was found to be 2.1%. 



