Hemosiderin is a hemoglobin-derived pigment, a golden-yellow or brownish-yellow granule, which is called iron-containing hemosiderin because of its iron-containing and golden-yellow color. When red blood cells are phagocytosed by macrophages, hemoglobin is broken down into iron-free orange blood plasma and iron-containing ferric hemosiderin by the action of lysosomal enzymes. Prussian blue reaction is also known as ferric hemoflavin staining, that is, after treatment with potassium ferricyanide and dilute acid, blue color can be produced, which is commonly found in phagocytes or mesenchyme, and the principle of staining lies in the fact that the trivalent iron ions are separated from proteins by dilute hydrochloric acid by the solution of potassium ferricyanide, and the trivalent iron reacts with potassium ferricyanide to produce an insoluble blue color compound, i.e. ferric ferric ferritin of trivalent iron. The reaction between trivalent iron and potassium ferricyanide produces an insoluble blue compound, ferricyanide of trivalent iron. Leagene Prussian blue stain (Perls Stain) is used to show various hemorrhagic lesions in local tissues, which is commonly found in phagocytosis cells, and it can distinguish ferricyclohexanin from other pigments well. The stain is stable, can be stored for a long time, is not easy to produce precipitation, and has a wide range of applications, and can be restained with red coloring agents such as nucleus-fixing red, eosin, neutral red, and so on, after reaction. The red staining solution of this staining solution adopts nuclear solid red, which is the most classic and commonly used method of re-staining.