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The peroxidatic activity of hemoglobin permitted visualization of its uptake by rat hepatocytes by means of the Graham-Karnovsky 3,3'-diaminobenzidine (DAB) procedure. Lysosomes were visualized by their acid phosphatase, beta-glucuronidase, and glucosaminidase activities. When large doses of rat, cow, or human hemoglobin are intravenously injected, or when hemoglobinemia is induced by injection of distilled water, DAB-positive hemoglobin is engulfed by pinocytosis. Pinocytotic vacuoles become digestive vacuoles ("phagolysosomes") by fusion with lysosomes of the dense body type that have moved from their pericanalicular position. By 16-24 hr after even massive amounts of hemoglobin (400 mg/100 g), the protein is barely demonstrable in hepatocytes. At the lowest doses of injected hemoglobin (15 mg/100 g body weight), DAB-positive vacuoles are demonstrable only in the Kupffer cells.