Some remarks on red cell shape and on surface and volume relationships.

Red cell (RBC) form is of interest for its own sake and for its role in characterizing physiologically altered and pathological cell types. RBC shape is also identified as one of the three principal factors enabling (and limiting) flow-induced cellular deformability processes. It has become common practice to discuss and analyze RBC form in terms of the ratio of the cell's surface area to its volume, and indeed to use the two concepts interchangeably. The inadequacy of the S/V ratio to serve this purpose is pointed out, a long with the qualitative and quantitative errors that it leads to, with cells of either very small size (as in iron-deficiency anemia) or large size (as in Addison's associated anemia). The substitution of a normalied, dimensionless, relative surface-to-volume function that can accurately quantitate this facet of form is necessary. The relationship between this function and other measures of form and "sphericity" are specified, and some applications of these functions to studies on cell form and deformability are indicated.