Inbreeding of the Lewis rat is begun by Dr. Margaret Lewis from a Wistar stock. In 1924, at F20 to Aptekmanm and Bogdon. In 1958, at F31 to Silvers, who distributed this strain. subsequently. LEW/SsNSlc rats were descended from a colony obtained from the National Institutes of Health, Bethesda, Maryland USA in 1994 to Japan SLC, Inc.,Shizuoka, Japan.