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1. A dose of 1.0 million roentgen equivalent physicals of high-voltage cathode irradiation will adequately sterilize one-eighth-inch-thick sections of freeze-dried and frozen animal bone after bacteriological contamination with Staphylococcus aureus (F.D.A. 209).2. This sterilizing dose does not significantly impair graft healing in the dog.3. Cathode irradiation of dog-bone grafts at 2.0 to 6.0 million roentgen equivalent physicals results in some impairment of healing in freeze-dried grafts; whereas, it appears to accelerate the healing of frozen grafts. This advantage for frozen irradiated bone is out-weighed by the superior rate of incorporation of freeze-dried as compared with that of frozen grafts.4. Irradiation causes gross and microscopic changes in bone grafts. These consist primarily of a yellow discoloration prior to implantation, increased basophilic staining after implantation, and some impairment of the "cement line" between the graft and the invading host bone. These changes are roughly proportional to the dose of irradiation.5. Before carrying out controlled clinical studies in patients, an experiment should be performed to determine the doses necessary to sterilize sections of various sizes of human bone that have been grossly contaminated with mixtures of a wide variety of organisms.