Fouchet-Van Gieson kit is used for simultaneous visualization of bilirubin and collagen in histological samples. Bilirubin is a yellow-brown pigment created as a result of hemoglobin degradation. Hemoglobin degradation occurs in bone marrow, spleen, and liver. In the case of patients that suffer from hepatitis, bilirubin builds up in the form of thrombus in bile ducts and in the form of granules in hepatocytes and in the cytoplasm of Küpfer cells. The pigment is insoluble in water and in water fixatives. However, in cases of prolonged exposure to formalin fixatives it may turn green. The color that is created during staining using the Fouchet-Van Gieson kit is due to the strong oxidoreduction of the complex and subsequent conversion to biliverdin (green). The false-positive reaction may be checked using HemoGnost Perls kit – in that case Perls’ reaction will always be negative to bilirubin.