This is a low-power photomicrograph of a normal appendix on the right and an appendix with acute inflammatory response on the left. Note the abundant blue-stained lymphoid tissue beneath the mucosal layer and the absence of blue-staining cells in the submucosal layer of the normal appendix. Compare this with the extensive distribution of cells throughout the wall of the appendix with acute appendicitis. The blue color is due to the presence of many inflammatory cells, although at this low power these individual cells cannot be specifically identified.