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It should be emphasized that this is a preliminary report and that no valid conclusions can be drawn from so few cases. However, it is encouraging to have definite acceleration of hone growth in four cases of poliomyelitis occurring respectively at three, four, five, and six years after onset of the disease, coincident with growth-stimulating procedures. This suggests that the cells in the cartilage columns of the epiphyseal plates have not undergone degenerative changes during these periods, as would be anticipated from Harris's hypothesis. Further study to determine when and if these premature senescent changes occur is needed.Much remains to be learned about bone growth in children. Although all of us are familiar with conditions which produce overgrowth of the long bones, we do not know in what percentage of cases this overgrowth persists, or in what percentage of cases there is premature ossification of the epiphyseal plates.From the conflicting reports in the literature on the results of animal experiments on growth stimulation, it is obvious that animal experimentation is not as yet a reliable tool for the study of growth stimulation of long bones.Although ivory is being used almost exclusively for bone-growth stimulation, a word of caution should be given concerning the use of metals. Reports of experiments in animals have indicated that certain metals are toxic, notably magnesium.There are many problems concerning bone growth which are waiting to be solved. It is hoped that this paper will serve to stimulate thought in this direction.