Physiologically, bones are composed of calcium phosphate salts (65%) for hardness, and a collagen
matrix (35%), for
flexibility. If a bone is placed in an acid bath and all the calcium is removed from it, leaving just the collagen matrix, when subjected to stress it will bend, not break. Conversely, if the collagen matrix is removed and all that remains are the calcium salts, when subjected to stress it will shatter.