584 ADVENTURES IN RADIOISOTOPE RESEARCH 



the vessel containing the radio-thorium preparation. The tube containing 

 the blood is placed in a small wash bottle. After leaving the wash bottle, 

 the oxygen stream passes through four more wash bottles containing 

 vegetable oil, which absorb all or most of the thoron still present in the 

 oxygen stream. The activated blood is then gently shaken at room tem- 

 perature for 30 minutes; 9 ml are reinjected into the patient, a known 

 aliquot of the rest being applied to prepare a standard sample as described 

 above. We found it less advantageous to incubate blood at 37° C than 

 at room temperature. 



Instead of leading thoron containing oxygen through blood, we can 

 dissolve the "active deposit" of thorium collected on the surface of a 

 platinum foil in blood. Most of the ThB introduced into the blood accu- 

 mulates in the corpuscles, though not to such a large extent as after 

 thoron activation. After 30 minutes incubation at room temperature, 

 about 6 per cent of the ThB is still found to be present in the plasma. 

 When choosing this method of labelling red corpuscles we have, there- 

 fore, to replace the active by an inactive plasma before injecting the 

 labelled blood. In the above experiments, the active deposit of thorium 

 w^as collected* for 24 hours, on the surface of a platinum foil connected 

 with the negative pole of a 220 volt (or preferably 300 volt) circuit. 

 The platinum foil is then placed in the blood sample, which is gently 

 shaken at room temperature for 10 minutes. The blood is then centri- 

 fuged, and the active plasma replaced by inactive plasma, before the 

 blood is injected into the circulation. 



Evaluation of the Activity Figures 



As already mentioned, we measure, besides the counts produced by 

 the rays emitted by ThB, to a large extent those emitted by ThC and 

 its disintegration products. Since practically all ThB is taken up by 

 the red corpuscles, the plasma does not contain this radioelement; 

 it contains, however, appreciable amounts of the bismuth isotope, ThC, 

 which does not accumulate in erythrocytes. Some of the ThC present 

 in the plasma of the injected blood escapes in the course of the experi- 

 ment through the capillary wall, while the ThC present in the standard 

 sample has no way of escape. The ratio between the activity of the stan- 

 dard sample and a secured sample shortly after securing the latter does 

 not, therefore, afford a correct measure of the circulating blood volume, 

 as indicated by the formula stated below. We can correct for the loss 

 of ThC from the circulation during the experiment, or we can avoid such 



* The collecting vessel used is decribed among others in W. Makoweb and 

 H. Geiger, Practical Measurements in Radioactivity. London (1912) and in G. 

 Hevesy and F. A. Paneth Manual of Radioactivity. London (1938). 



