The structures stained black in the image are

• A. Nerve fibers
• B. Neurons
• C. Glial cells
• D. Blood vessels

Answer: (A)

Silver impregnation stains neural processes to appear dark, highlighting the long, threadlike fibers that make up nerve fibers. In this image the black structures are these slender, elongated elements forming a network, which is characteristic of nerve fibers stained by silver methods that bind to neurofilaments and related components in axons and dendrites. Neurons would be expected to show cell bodies with nuclei rather than continuous dark fibers. Glial cells are small and form numerous nuclei rather than long, fiber-like tracks, and blood vessels would appear as hollow tubes with lumens rather than dark filamentous bundles. So the structures staining black are nerve fibers.