The effect of development on the composition of a long bone of the pig, rat and fowl

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Abstract
The humerus of the pig was analysed at various stages of pre- and post-natal development, and the femur of the rat and fowl at various stages of postnatal development. In the cortical bone, species differences were found in the time of life at which the major changes in composition took place and also in the magnitude of these changes. Rat bone at 158 days was more highly calcified than pig bone at one year or fowl bone at 27-42 weeks, but newborn-rat bone was in many ways comparable with that of pig fetuses at 46 days'' gestation. The prenatal epiphysial development of the pig''s humerus was a little more advanced than that of the femur at the same age. At birth the epiphysial development of the pig''s femur was considerably more advanced than that of the rat''s femur. In the dry fat-free epiphyses of the rat femur the fall in the percentage of non-collagen nitrogen during the first 56 days of post-natal life was accompanied by a rise in percentages of both collagen and calcium. After 56 days the percentage of collagen also fell, but that of Ca continued to rise. In the whole fresh bones of the pig and fowl the fall in the percentage of water during later postnatal growth was largely due to an increase in the percentage of fat. In the rat there was no increase in the percentage of fat with age. In all three species the fall in the percentage of water in the fat-free bones resulted mainly from a rise in the percentage of minerals. There was a significant fall in the degree of calcification of the pig''s humerus between 65 days'' gestation and term when the epiphyses were excluded. The major part of this fall was probably due to a fall in the degree of calcification of the metaphyses.