The separation of normal human leukocytes by density and classification by size.

T HE SEPARATION of morphologically distinct cells by differences in their specific gravity has been demonstrated using density gradient centrifugation in several support media. From bovine serum albumin density gradient centrifugation experiments, morphologically similar lymphocytes have been shown to consist of several closely spaced, discontinuous, discrete populations.5 In addition, erythrocytes have been shown to become smaller and denser while aging in circulating blood.#{176}8 Physical differences between morphologically similar cells ( i.e., density and size ) may indicate different functional properties of the cells. A Coulter counter, in conjunction with an electronic multichannel pulse-height analyzer system, can detect small differences in cell volumes which may be overlooked