1. Positive correlations at the 0.01 significance level occur between the fatigue life of bone and the percentage of osteons and of osteons plus fragments in the break area. Equally high negative correlations are found between the fatigue life of bone and the percentage of interstitial lamellae in the break area.
2. These correlations suggest that osteons tend to increase the fatigue life of bone and interstitial lamellae to decrease it. Osteons and interstitial lamellae have the opposite effect on the static tensile strength of bone.
3. Osteons are analogous to sticks, thus the more osteons in a given bone specimen the longer its fatigue life. Conversely, the more interstitial lamellae in a specimen, the fewer the number of osteons, and the shorter is the fatigue life.
4. Failure of a bone specimen under repeated flexure loading is comparable to breaking a stick by bending it back and forth. Thus, a bundle of sticks must be bent back and forth more times, that is, it has a longer fatigue life, than a single stick.