RESEARCH on the biochemistry of melanogenesis can be divided historically into three periods. 1 1. The identification of tryosinase, in 1895, by Bertrand and Bourquelot in certain varieties of mushrooms. 2. The demonstration of "dopa oxidase" in human skin, in 1917, by Bruno Bloch and the elicitation of some of the chemical steps in the conversion of tyrosine to melanin, in 1920 to 1930, by Raper. Bloch and his collaborators believed that dopa oxidase was found to occur specifically in mammalian skin. Raper carried out a thorough study of the intermediate reactions involved in the conversion of tryosine into melanin by tryrosinase in plants and meal worms. During this period there was a vigorous controversy over the mechanism of melanin formation in man, since tyrosinase could not be demonstrated in mammalian tissue. Human skin contained an enzyme which could catalyze the oxidation of dopa to melanin, but dopa had not