Abstract
1 . Fresh bone autografts to a muscle bed in the rat gave rise to vigorous new bone formation from about the fourth day. The graft took the form of a hollow ossicle with central bone marrow at eighteen days: it became progressively more regular in outline and was still present at six months.
2. Fresh bone homografts produced two separate phases of new bone formation–early and late. In the early phase non-lamellar woven bone appeared at about the fourth day, continued to grow until eight days, and subsequently died. It arose from osteogenic cells of the homograft. In the late phase, which developed in relation to a few grafts after four weeks, the new bone was lamellar in character, and remained closely applied to the graft surface. Evidence is presented that this bone arose by metaplasia of the host connective tissues at the graft site. There was a local inflammatory response to the bone homograft.
3. Both phases of homograft new bone formation were abolished if the animal was prepared by a skin homograft from the same donor four weeks before, but not if four months elapsed between the two grafting procedures.
4. Freeze-dried bone homografts did not give rise to the early phase of homograft new bone but produced a few examples of the late phase after five months. The inflammatory response was less intense with freeze-dried homografts than with fresh homografts.
5. Skin homografts three weeks after fresh bone homografts from the same donor underwent an early rejection at five to six days.
6. Skin homografts three weeks after freeze-dried bone homografts from the same donor had a mean survival time of twelve days, which was significantly longer than the mean survival time of l0·9 days in normal rats.
