Abstract
1. Three groups of one month old rats were fed for a period of four to five weeks on a rachitogenic diet (group R), the same rachitogenic diet with vitamin D (group N), and a complete diet (group S).
2. Young's modulus of elasticity E for bone can be derived from measurements of the deflexion of the centre of a femur loaded at the centre and supported at its ends.
3. The three different diets produced significant differences in breaking stress SB, Young's modulus E, and percentage ash in the bones. It has not been shown conclusively that higher ash content alone is responsible for the greater SB and E values of bones produced on the better diets.
4. The value of E in group R was 0·6 x 106 lb./in.2; in group N 1·0 x 106 lb./in.2; and in group S (which can be taken as normal) 1·6 x 106 lb./in.2.
5. There is a high correlation between SB and E even when the effect of diet is eliminated.
6. Although the bones produced on the good diet (group S) were much stronger than those of groups N or R, the strain at the elastic limit was the same (about 1·5 per cent.). The strain at rupture tended to be higher in groups N and R than in group S.
7. The properties of bone as a structural material are discussed.
