The specific defect in molecules of sickle hemoglobin (HbS) has been known for many years (1), but the nature of the assembled polymers of HbS which distort susceptible erythrocytes remains unclear. Several structural forms of sickled hemoglobin have been observed in electron microscopic studies, including a mat-like arrangement of fibers (2), empty hexagonal crystals (3), microtubules (4), and...