Inasmuch as the cases of acute pleurisy with serous effusion, the cases of hypodermoclysis, and experiments with saline injection into cortical bone and periosteum present swelling of periosteum and bone with enlargement of lacunae and interlamellar spaces and activity of the bone cells and periosteal cells, the writer judges these to be a preliminary step to the formation of new bone. The bone is softened, calcium salts are carried into surface-degenerating tissues, and the modified, slowed, congested circulation stimulates the formation of new bone.