Histological sections of 178 large-fragment and small-fragment fresh autogenous and homogenous bone implants in the anterior chamber of the rat's eye, studied for as long as thirty weeks after implantation, revealed the following:
1. Fresh large-fragment cancellous autografts gave rise to early vigorous new-bone formation which produced an ossicle incorporating marrow substance about three weeks after implantation. The shape of this ossicle appeared to be determined by the stresses in the anterior chamber of the eye. There was no inflammatory reaction, and the bone continued to grow throughout the experimental period.
2. Fresh large-fragment cancellous homografts produced early new bone, but this died at the end of two weeks. A late phase of bone formation composed of scanty lamellar new bone appeared at eight weeks and still persisted at the end of the experiment thirty weeks after implantation. A mild local inflammatory reaction was associated with this implant.
3. Fresh large-fragment cortical autografts and homografts produced scanty, lamellar new bone which was closely applied to the graft surface. The cortical homograft in contrast to the autograft produced early-phase and late-phase new-bone formation, as well as a mild local inflammatory reaction.
4. Small-fragment fresh cancellous and cortical autografts and homografts did not produce any appreciable new bone. A more intense inflammatory reaction was incited by this type of graft than by the large-fragment bone implants; this reaction enhanced the process of resorption of the small-fragment transplants.
5. The evidence from these studies indicates that cellular elements of the large-bone fragments may survive and proliferate in the anterior chamber of the rat's eye to produce new bone in the early period following transplantation. Fragmentation of bone, however, creates a medium unsuitable for cellular survival and destroys the osteogenetic activity of the graft.
6. New-bone formation brought about by metaplastic change in the host cells in these experiments appeared to be the result of prolonged direct contact with large-fragment homografts until the late-phase new-bone formation had developed. Similarly, the two solitary instances of late-phase new-bone formation associated with small-fragment grafts (homogenous cortical and cancellous and autogenous cortical) appeared to be examples of new bone induced by contact of the transplanted bone tissue with the host cells.