It is possible to combine variations in density and size to allow for separation of cell populations within the earth's gravitational field, i.e. without a centrifuge. A technique devised by Miller and Phillips 14 uses a 3-30% gradient of fetal calf serum in phosphate buffered saline, coupled to the use of a specially designed sedimentation chamber.
The technique substitutes time for the expense of a centrifuge, but also keeps the cells from being subjected to increased gravitational forces. Several commercial applications of this technique are now available for the separation of blood cells within reasonable times (24 hours). Miller and Phillips used the technique to separate spleen cell suspensions and sheep erythrocytes. The technique is particularly valuable for the separation of cells of the hemopoietic system, prior to sub-culture or analysis.
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