Incidental to the course of an investigation of an entirely unrelated problem there developed in several rabbits lesions of bone with all the characteristics of cartilaginous exostosis and in two rabbits tumors apparently identical to the giant cell tumor of man. These observations are reported because it is believed that they contribute some information relative to the etiology of these tumors.
The studies were made on fourteen immature rabbits from 1 to 3 months of age. In each a segment measuring approximately 20 mm. was removed from the shaft of the radius on both sides in block resections. In each animal the gap on the right side was bridged with an autogenous transplant of costal cartilage equal in length to the segment of bone removed, and on the left side it was left empty to fill with blood. The results of the original problem, which had for its purpose a