Macrophages are cells referred to as "big eaters" or "killing machines" that destroy any foreign agents (pathogens) or antibodies found in the body. When a pathogen is detected, the macrophage moves toward it and literally devours it almost instantly. Suppose a large number of pathogen molecules are lined up 1.0 mu m apart on a straight fiber of tissue. A macrophage initially 0.50 mu m from the nearest one moves toward it at a constant speed of 30 nm/ s}.