“…There is abundant evidence that the cocoon fibers produced by the larvae of the silk moth Bombyx mori have a filamentous fine structure (14,16,20), but no clearly defined microfibril of the type encountered in other fibrous proteins such as feather keratin (4) and mammalian keratin (1,17) has been recognized so far. Early studies of B. mori silk fibroin by X-ray diffraction techniques (2,9) revealed that it contained crystallites which were elongated parallel to the fiber axis but of limited extent or poor regularity at right angles to this direction.…”