In two recently published papers, experimental studies on rickets were described, which indicated that a hitherto unknown relation exists between an unappreciated function of the bone marrow and the processes of calcification and ossification. These studies would seem to show that the marrow produces an organic substance which is essential for normal bone formation. The foregoing conclusion could be drawn from the fact that bone marrow given by mouth, or extracts of healthy bone marrow given hypodermically, induced healing in the bones of rats with rickets. No such effects were obtained from the marrow of rachitic bones. From these experiments it is obvious that the formation of normal bone is closely connected with a normal organic function of the bone marrow, and that the disorders of calcification and ossification in rickets may be closely connected with, or due to, pathologic changes in bone marrow function. These changes are most probably