When overweight is added to normal bone a relation forms with its transformation. Therefore, the author made experiments on normal adult dogs by resecting parts of their radial bones and giving overweight to its ulna to see what attitude it took. 1) The main X-ray findings were the decrease of physiological curve of the bone and the spindle shaped periostal callus at the part getting the greatest overweight. 2) It was concluded from the distribution of stress and strain in the inner part that the part producing future dynamic callus was the same as the place receiving maximum stress before its thickening. Stress as well as production of callus seen in the compressed part of the concaved side was much greater than that of the retracted part of the convexed side. Stress appearing in the bone after its thickening was generally reduced comparing to its previous state and stability was formed. Comparing to normal bones decrease of the curve helped in reducing stress. 3) Changes seen in nutritional arteries by arteriography showed complicated distribution and fine shadows. Formation and dilation of new vessels were also seen histologically in dynamic callus and bone. 4) Histologically it was mainly the development of periostal callus. There was dilation of Haver's canal and its passage was irregular with its inner vessels dilated and showing
hyperemia. Hyperemia, new development and intrusion of vessels were obvious also in the callus.