| Summary: | Some of the earliest studies of the blood volume have been in those conditions associated with anemia or polycythemia. The obvious questions that present themselves are; does anemia truly represent a reduction of the red cell mass or is it merely apparent because of an increased plasma volume; is the polycythemia due to an increased red cell mass or a reduction of the plasma volume? Indeed, the early workers suggested that chlorosis was an apparent anemia only, with a normal red cell mass, and that pernicious anemia was a true anemia. The importance of a three dimensional view of the state of the blood can be readily appreciated. The variety of methods for the determination of the blood volume that have been utilized by various individuals merely attest to the fact that an ideal method remains to be discovered. The variety of modifications of a single method, and there is hardly an investigator whose method has not been slightly altered from that of the next, is evidence of the hope that these changes will add to the accuracy of the method. By this time, a fairly good understanding of the factors affecting the blood volume determination has been established. By the application of these factors, a reasonably accurate determination of the plasma volume and the red cell mass may be made independently. The determination of the plasma volume, however, does not give a sufficiently accurate estimate of the cell volume, and vice versa.[...]
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