"THORIUM B" IX BLOOD VOLUME STUDIES 587 



The procedure cannot be used when the result is wanted urgently. 

 In such cases we centrifuge the blood sample before injection, and replace 

 the active by an inactive plasma, thereby removing the disturbing ThG 

 present in plasma. Applying this procedure we can also obtain labelled 

 red cells by dissolving ThB collected on the surface of a platinum foil, 

 which is then placed into the blood sample. This type of activation of 

 the blood sample takes only a few minutes. 



Decaying actinium supplies emanation (acton) as well, which in tuin 

 produces in the blood sample AcB, which has the same chemical pro 

 perties as ThB, and AcC which has the same chemical properties as ThC. 

 While one-half of the ThC present decays in one hour, the half-life of 

 AcC is only 2.2 minutes, and this product correspondingly disappears 

 from the plasma of activated blood in a few minutes. We are at present 

 investigating the possibility of applying AcB-labelled red corpuscles in 

 circulation studies. 



Calculation of the Blood Volume 



If we inject G gm of labelled blood, express the activity of the secured 

 sample by P, that of the standard sample by S, and the dilution figure 

 of the standard sample by D, the blood content of the human subject 



SG 

 in gm X works out as X . We then compare the activities of 



100 mgm of dry blood of the secured and of the standard sample, or the 

 activities of these samples after being poured into cuvettes. It is assumed 

 that all ThB is concentrated in the corpuscles; in fact, about 1 to 2 per 

 cent of the ThB content is located in the plasma. About four-fifths of 

 this ThB leaves the circulation within a few minutes. Correspondingly, 

 the above formula overestimates the blood content by about 1 per cent 

 and should be replaced by 



^ 0.99 SG 

 X = 



PD 



If, for example, S = 2000, P = 200, G = 10 g and D = 0.02, X 

 works out as 4950 gm. 



Should we wish to compare the activity of cuvettes, one of which 

 contains hemolysed blood, while the other (the standard sample) contains 

 a hemolysed suspension of red corpuscles in saline, owing to the somewhat 

 lower absorbing power of the latter sample for /9-rays, we have to multiply 

 the above formula by 0.95. 



While Zerahn's cuvettes are most convenient for use in determining 

 the circulating blood volume, the high water content of the 1.5 cm 



