Young rats were killed at varying time intervals after the administration of radio-active calcium (Ca45). The specific activities of radio-active calcium were determined for various parts of the skeleton.
It was found that the ratio of the specific activities of diaphyseal bone to that of epiphyseal bone rose continually from a value below unity to a value above unity over an interval of as long as sixty-seven days between the administration of the radio-active calcium and the death of the animals.
This means that during this time no state of equilibrium was reached between different parts of the skeleton and body fluid with respect to the distribution of radio-active calcium. It was further shown that the redistribution of radio-active calcium in different parts of the skeleton varied with the rate of growth of these parts.