RED COKPUSCLE CONTEXT OF THE CIRCULATING BLOOD 571 



the correct value of the blood volume makes out 91 per cent of the value 

 determined by the dye method. 



On the other hand, when the blood volume is calculaled irom the 

 corpuscle volume determined by the ^^P method and the hematocrit 

 figure, we obviously underestimate the blood volume. Now, if we over- 

 estimate the hematocrit value, \v(^ underestimate 1lu> slian^ of the 

 plasma in building up the ))lood and, thus, we underestimate Ihe blood 

 volume. 



If the CO method would supply us with a correct value for Ihe cor- 

 puscle content of the circulation, the blood volume calculated from the 

 corpuscle volume and the hematocrit figure would be too low. However, 

 as the CO method provides us with a too high value for the corpuscle 

 volume, the opposite is the case. The error due to the uptake of CO 

 by other compounds than the hen:oglobin present in the circulating 

 blood, overcompensates the error due to an underestimation of the 

 plasma content of the blood. 



Determination of the red corpuscle volume by using radio-iron as an 

 indicator 



While Hahn and Hevesy (1940) and Hevesy and Zerahn (1942) 

 carried out a determination of the corpuscle content of the rabbit and 

 the hen by labelling the corpuscles with radio-phosphorus, Hahn, 

 Balfour, Ross, Bale and Whipple (1941) used radio-iron as an 

 indicator in experiments with dogs. Radio-iron is more stably bound in 

 the corpuscles than radio-phosphorus. This fact makes possible to carry 

 out experiments of several days duration. Experiments lasting only a 

 few minutes lead to the same results regarding the corpuscle content as 

 experiments lasting a few days, which proves that the mixture of the 

 corpuscles injected with those beforehand present in the circulation had 

 occurred already in the course of a few minutes. 



In contradistinction to the labelling of corpuscles with radio-phospho- 

 rus which can be carried out in in vitro experiments, the labelling of 

 corpuscles with radio-iron can only be made in vivo. In experiments on 

 human subjects, it is necessary to work with donors whose blood was 

 labelled with radio-iron .By making use of this procedure in order to 

 obtain corpuscles of sufficient activity, very substantial radio-iron 

 activities had to be administered. However, the preparation of even 

 moderate iron activities — in contradistinction to that of large phos- 

 phorus activities — is a difficult task. This may be the reason why 

 so far only animal experiments were carried out with radio-iron. 



When using radio-iron as an indicator in the experiments with dogs, 

 Hahn and his colleagues found a smaller corpuscle content than that 

 obtained by a calculation of the corpuscle content from llic plasma (dye) 



