The densities

See Equation in the PDF file

of the cervical vertebrae, thoracic vertebrae, lumbar vertebrae, sacra, ribs, humeri, radii, ulnae, femora, and tibiae from eighty adult skeletons were determined. The skeletons were derived equally from American whites and Negroes of both sexes, each group with a wide age range. The weight of the bones was determined with the bones in a dry, fat-free state, and the volumes were measured by displacement of millet seed.

It was found that:

1. In both white and Negro males the mean densities of radii, ulnae, and tibiae did not differ from each other, but they were significantly higher than the densities of ribs, humeri, and femora which did not differ from each other; cervical vertebrae were significantly less dense than the last-named series, but denser than the thoracic vertebrae and lumbar vertebrae and the sacra, which likewise did not differ from each other. In females of both races the mean densities of the five long limb bones and ribs did not differ from each other, but they were significantly higher than the densities of the four segments of the vertebral column which did not differ significantly from each other except that the cervical vertebrae were significantly more dense than the sacra in white females.

2. The density of each bone series in each sex-race group decreased witih age although not significantly so in eleven of the forty slopes studied. The combined slope of the densities of the ten bone series in each sex-race group decreased significantly with age. The decline occurred at approximately the same rate in each bone series within each group.

3. After correction for age differences among the four sex-race groups the four mean densities of each bone series (except the ribs and femora) differed significantly. The difference in cervical vertebrae, in humeri, and in ulnae was attributable to sex (male bones denser than female and to race (Negro bones denser than white). In the radii and in tibiae the difference was attributable to sex only; and in the thoracic vertebrae, in lumbar vertebrae, and in the sacra, to race only.

Thus, from this study of ten series of bones from the same skeletons it was found with only few exceptions that long limb bones and ribs are denser than vertebrae; that cervical vertebrae are denser than the other segments of the column in males, but not significantly so in females; that bones of the Negro skeleton are denser than bones of the white skeleton; and that bones of the male skeleton are denser than bones of the female skeleton. Furthermore, it was suggested by this study that within each sex-race group bones decrease in density with age at a uniform and parallel rate.