False-colour scanning electron micrograph (SEM) of the surface of the colon mucosa, with clusters of bacteria attached. Rod-shaped bacteria, possibly Escherishia coli, a harmless inhabitant of the colon, occur in clusters (pink) on the surface of absorptive and mucous secreting cells. The colon produces faeces by absorbing water and nutrients from already digested food passing through it. Mucous secreting cells lubricate this food; cells with microvilli (tiny surface protruberances, seen here) are absorptive; these microvilli increase surface area which increases efficiency in absorption. Magnification: x2,350 at 6x7cm size. Magnification: x3,750 at 4x5 inch size.