The cells have spindle-shaped bodies and a thin rim of densely staining cytoplasm difficult to distinguish from the nucleus. The nucleochromatin is homogeneously dense, and the cytoplasm does not contain an abundance of organelles, although representatives of the usual components can be found. During normal wear and tear, some CNS elements degenerate and microglia phagocytose the debris (Fig. 1-16). Their identification and numbers, as determined by light microscopy, differ from species to species. The CNS of rabbit is richly endowed. In a number of disease instances, such as trauma, microglia are stimulated and migrate to the area of injury, where they phagocytose debris. The relatively brief mention of this cell type in the major EM textbooks [3] and the conflicting EM descriptions [33] are indicative of the uncertainty attached to their identification. Pericytes are believed by some to be a resting form of microglial cell. Perivascular macrophages, which are of bone marrow origin and are distinct from parenchymal microglia, also have been described.