Figure 4: A. Irradiated (25kGy) particulate cortical bone allograft (500 to 800 μm) six weeks post transplantation into an experimental animal. The allograft (arrow) remained virtually intact with very little bone formation in the periphery of the defect. This indicates absence of active osteogenesis. B. Irradiated (25kGy) demineralized cortical bone allograft (500-800 μm), six weeks after transplantation into an experimental animal. Active osteogenesis is absent as observed in the irradiated non-demineralized graft.