Colored proteins are the biochemist's delight. Indeed, perhaps this chemical property, rather than ubiquity or ease of isolation, really explains why both hemoglobin and ferritin — the red and the golden-brown proteins — have been prominent interests of protein chemists for over 30 years. No less are colored proteins the clinician's province. They produce complexions from pallor to plethora — and pathologists have long recognized the dark-brown appearance of ferritin-laden spleens and livers. These two colored proteins, brothers in trade, contain the bulk of the body's iron. Ferritin subserves the important function of hemoglobin formation. The ferritin molecule has a . . .