THE STRENGTH AND ELASTICITY OF BONE IN RATS ON A RACHITOGENIC DIET

摘要: One of the aims this work was to find criteria by which quality bone as a supporting tissue might be judged. This inevitably involves discussion and, if possible, assessment, relative importance inorganic and organic material bone. It is relatively easy measure mineral content, for that reason it has always received more than its due share attention. In present experiment composition ash all bones remarkably constant, with Ca/P ratio 2. Furthermore, X-ray crystallography showed structure same in cases. The great difficulty measuring variations is, course, protein nature makes impossible say how much influences strength. Since at least 40 per cent. collagen, either quantitative or qualitative alteration alter revealed no differences collagen three groups; so would seem safer assume alterations physical properties are proportions constituents (Dawson 1946, Bell et al. 1947). These experiments show diets produce highly significant percentage ash, SB, E. possible some absolute (weight unit volume substance); but range variation leaves reasonable doubt between diet groups essentially ash. Presumably contributes something strength bone; indications plays minor part weakness flexibility rachitic decrease content. Within any one group, relation other two variables, SB E, masked sources such those associated many measurements involved; thus correlation also not significant. At first sight, scatter diagrams (Figs. 5 6) appear indicate Closer inspection shows, however, apparent trend largely means groups, points within group obvious trend. Figure 7 shows position regard E very different. Here there an each group; amount less. Calculation that, even when excluded, still question variables discussed fully addendum paper. Although "goodness" usually judged breaking stress, experimental findings recorded above suggest may assessed equally well on basis elastic shown Young's modulus. Normal bones, S these experiments, were up 79 their stress (Table II): poorer R N were, only little inferior respect. In cases deviation load-deflexion curve from straight line until about break. Such published paper series (Bell, Cuthbertson Orr 1941), light further experience scarcely typical. terminal falling over illustrated 4 marked R. While upper limit elasticity varies wide II Fig. 4), strain point constant 1·5 displacement must occur molecules limit—and molecular displacement, deformation reversible; beyond it, plastic changes occur. We have evidence whether limiting concerns bone, both. We already commented remarkable (Bell , 1941). normal rat cast iron, half mild steel. modulus, one-tenth iron one-twentieth Thus despite lightness (specific gravity 2·5 compared 7·9 iron), strong time flexible expected. biological advantage greater helps absorb sudden impacts. unusual metallic substances modulus proportional strength; characteristic materials like concrete timber. Another property remains three-quarters stress. Most metals considerable ductility before reaching point. While interest, both own account index close association suggests used predict maximum load can carry safely. unlike measured without damage, useful information gained living human bones.