“…A widely practised method of producing such a deficiency is by the use of thyroid-active materials like iodinated casein. Young growing animals fed on diets supplemented with thyroprotein were therefore used by early investigators (Zucker & Zucker, 1950) for assays of liver preparations. In the presence of an ample supply of other nutrients, iodinated casein induces retardation of growth and subsequently a high mortality, which are partially counteracted by supplementation of the ration with vitamin B12 (Emerson, 1949;Cuthbertson, 1949;Sure & Easterling, 1950;Graham, Reichstein, Watson & Hier, 1952).…”