Fifty-six years ago (1874) Wegner1 showed that inorganic phosphorus administered in small doses, as was formerly the practice in the treatment for rickets, causes the freshly forming trabeculae at the ends of the shafts of the long bones to multiply and become closely packed together. To this dense, thicket-like formation of trabeculae at the end of the shaft induced by phosphorus Wegner gave the name "osteosclerosis." Years later (1918) Phemister2 discovered that dense shadows appear in the x-ray photographs of the long bones of children after the administration of minute doses of elementary phosphorus for five weeks or more. These shadows appeared in the parts of the shaft that were in process of growth during the administration of phosphorus and continued to form, so Phemister thought, for a time after the phosphorus had been stopped. Since the long bones grow in length at their ends because of the