Morphologic appearance of fresh, unfixed samples of initially profoundly dehydrated RBCs at different times of incubation in culture media. RBCs in culture medium were observed under phase contrast at × 630 (Zeiss photomicroscope III RS; Zeiss Planapo objective lens, ×63 magnification, 1.4 numerical aperture). Photographs were taken with a JVC color video camera, TK-C1381. Note the gradual appearance of smooth, flattened discs, some with typical biconcave shape, indicating spontaneous rehydration of RBCs. This explains the developing heterogeneity apparent in the osmotic fragility curves of Figure 2B.