The rat was injected with a red dye the day before the sample was prepared. Macrophages (HA2, M) are obvious in this spread because they phagocytosed the dye. Macrophages are generally elongated or bipolar cells, with nuclei that are smaller, more elongated, and denser than nuclei of fibroblasts. The clear areas between cells and fibers in this micrograph and in HA1 and HA3 are ground substance.