Since McEwen's classical work on bone repair, there has been much uncertainty in the minds of clinicians regarding the process that occurs in bone repair following injury. Whether or not the periosteum is the all-important factor in osteogenesis has clouded our minds. The significance of the bone cell, of the periosteum, and the significance of intermembranous or of intercartilaginous bone development is not known. The terms after long usage are established as entities, thus tending to suggest biologic differences because of microscopic difference. Until the physical chemist gets at the root of things, confusion concerning bone in all parts of the body will exist in the minds of laboratory workers. I believe when the real secrets of bone formation are understood, we shall acknowledge that osteogenesis occurs in the same manner in all tissues. The tissues that are seemingly different under the microscope, I believe, are chemically similar whenever osteogenesis