A Polarized Light Analysis of the Human Red Cell Ghost

1. A new method is described for measuring the thickness of thin spherical birefringent membranes. It consists of measuring a curve of retardation against radial distance at the edge of the membrane, and comparing this curve with other curves calculated from theory for membranes of known thickness. Diffraction is taken into account. 2. This method shows that the wet thickness of the human red cell ghost in glycerol is about 0.5µ. A good agreement with the experimental results would be given by a model membrane consisting of a weakly birefringent layer 0.5µ. thick surrounded by a strongly birefringent layer 40 A. thick. It is suggested that the thick layer is a 2 % protein gel, and that the thin layer is a bimolecular layer of lipids. 3. The birefringence indicates that there is radial molecular and tangential micellar orientation in the protein gel. This can be explained by an arrangement of the protein chains in looped bundles. 4. On the basis of these results a new model is put forward for the structure of the red cell membrane, and some of its implications are discussed.