The first iodinated proteins which contained iodine in true chemical linkage were prepared by Blum & Vaubel [1898] and by Hofmeister in the same year; Hofmeister iodinated an aqueous solution of crystalline egg albumin and found that after repeated purification by dissolving in alkali and precipitating with acid, a product was obtained which contained nearly 9% iodine which could not be removed by physical means. Hofmeister suggested that tyrosine was involved in the reaction and showed that the protein no longer gave a Millon reaction. Acid hydrolysis of the protein gave an iodine-rich fraction which was insoluble in acid, soluble in alkali, and according to the author resembled in many ways Baumann's iodo-thyrin from thyroid. In 1899 Kurajeff prepared iodinated egg and serum albumins with iodine contents of about 12%, and he also observed that the Millon reaction was absent after iodination. In 1910 Oswald isolated di-iodotyrosine from hydrolysates of