Coloured scanning electron micrograph of the gram- positive bacteria Streptococcus pneumoniae (pneumonococcus), which is associated with pneumonia in humans. The bacteria are spherical & form characteristic chains. They secrete a viscous material to form a capsule around their cell wall. The role of the capsule is uncertain, but is associated with virulence in pathogenic organisms. It gives the bacteria protection against the immune system of the invaded host. Capsulated organisms resist phagocytosis (engulfing) by white blood cells. Magnification: x4, 000 at 35mm, x10,000 at 5x7cm size.