Liver fibrosis in one SD rat, where (A)–(D) correspond to stages F1–F4 (Masson stain, original magnification, 200 x).

Blue staining (white arrow) shows collagen fibers, and the black arrow indicates a fat vacuole. As the stage of liver fibrosis progresses, the accumulation of blue-stained collagen fibers gradually increases, which is associated with different degrees of steatosis.