Abstract
1. Measurements have been made of the relative calcification of different types of bone in tibia of the rabbit at the ages of six weeks, three and a half months and seven months by comparing their absorption of x-rays.
2. Calcified cartilage is between 8 and 10 per cet more highly calcified than periosteal and endosteal bone and about 20 per cent more highly calcified than bone formed immediately adjacent to cartilage.
3. Young and adult bones have a framework of approximately the same strength; that is, calcified cartilage, bone adjacent to cartilage and the interstitial areas of periosteal and endosteal bone have each approximately the same degree of calcification at all ages.
4. Adult rabbit bone approaches uniform calcification throughout, equal to the calcification of the interstitial areas of periosteal and endosteal bone. Evidence for this is the replacement of the lowly calcified epiphysial bone by osteones of higher calcification.
