The knowledge of tumors of bone and bone marrow is still in the descriptive stage. To reach a correct histologic diagnosis of the case and to provide some conception of the probable clinical course are all that can be expected at the present time, and often more than is accomplished. The separation of the numerous tumors of this group into well-defined clinical and pathologic entities is far from complete, while knowledge of the exact origins of these tumors and of their various exciting and contributing causative factors is extremely fragmentary, or, indeed, wholly lacking. Moreover, with the present trend of medical research, the prospects are not favorable to important progress in this field. Serology, immunology, chemistry, studies in nutrition, and the use of modern instruments of precision have contributed little and promise little in the study of bone tumors. Abundant clinical material, wide clinical experience, and knowledge of the embryology,