Macrophage attacking bacteria. Coloured scanning electron micrograph (SEM) of a macrophage white blood cell (brown) attacking a group of Borrelia sp. bacteria (blue, lower left). The macrophage has extended a long pseudopod towards the bacteria prior to engulfing them. Once engulfed, a process known as phagocytosis, the bacteria will be destroyed. Macrophages are white blood cells which attack many types of foreign organisms in the body, including bacteria. Borrelia sp. bacteria cause several diseases in humans, including Lyme disease and relapsing fever. Magnification: x640 at 6x7cm size. x1000 at 4x5"~LANDSCAPE"