In past years, scientific discussion of the problem of causal osteogenesis was dominated by the conflict between the osteoblast theory and the induction theory. The work of Orell and Levander in particular contributed evidence to both theories. In the present series of experiments, the important osteogenetic significance of the soft-tissue components of bone—periosteum, marrow, and living cells of the bone canals—has been established anew. Even in adults, the latent osteogenetic cells were brought to proliferation and function within several days by the activating influence of bone necrosis.

To determine clearly the effect of non-specific connective tissue of bone substance per se, autogenous frozen-bone grafts covered with periosteum were transplanted in the dog. Up to the fourteenth day no evidence of bone formation could be found on histological examination. The histological appearance of necrosis of the periosteum is to be regarded as proof of the fact that the osteogenetic tissue was completely killed by freezing. Since sparse new-bone formation and delayed bone regeneration of the graft took place after some time (even up to fifty-three days), a transformation of the non-specific connective tissue of the host into osteogenetic tissue must have taken place. Consequently, the osteoblast and induction theories are combined into a unified concept.

Bone regeneration occurs in two osteogenetic phases,—the first and, physiologically, most important phase originates in the pre-existing specific cells and begins after several days. The inception of the second phase, however, originating in the non-specific connective tissue, requires several weeks. Both phases, nevertheless, are stimulated by the activating influence of the bone necrosis.