1. In a fracture study of twelve selected adult rats, autoradiograms (with use of Sr89) showed that ossification seems to progress centripetally toward the interfragmentary space, and is generally more pronounced about the concavity of an unreduced fracture, The most extensive deposition of strontium in the callus appeared at about four weeks after fracture. A noticeable drop in strontium uptake by the fractured humerus appeared at about ten weeks.
2. In a limited chemical study of strontium deposition with a select group of twelve adult rats, findings were follows:
a. An elevated fluoride intake did not favor increased accumulation of strontium either in the fractured humeri or in the sound humeri and femora.
b. The precentage of strontium taken up by the fractured unreduced adult rat humerus was twice that deposited in the sound limb, the increase being attributable chiefly to uptake by the callus. This ratio dropped appreciably toward the end of the repair period.
c. Judging by the comparative uptakes of the femora and sound hueri, the relative distribution of strontium among the femora and humeri of individual animal (calculated as percentage of strontium) appeared to be related to the mineral content of these unfractured bones.
3. The reliability of measurements of relative breaking strengths of rat bones on a specially devised static-loadign assembly has been demonstrated, and results were found to be satisfactory when an average absolute deviation of 6 per cent was tolerable.
4. From the sixth through the twelfth week after unreduced fracture of the left humerus, adult rats on a stock diet received as drinking fluids solutions of strontium, fluoride, a combination of these or distilled water
a. Under the conditions of this experiment strontium, fluoride, or a combination of the two showed no significant effect upon the breaking strengths of the fractured ember.
b. There seemed to be no clear relation between the breaking strength of the repaired humerus and its roenstgeniographic appearance, histological findings, or the mineral regimen.
5. A constant intake of strontium, fluoride, or strontium fluoride over 180 days did not show any significant influence of these minerals (in the concentrations used) upon fracture resistance of the humerus and tibia or upon longitudinal growth of the long bones of adult rats.