Pneumococci are single-celled microscopic organisms (micro-organisms) called bacteria. Bacteria have all the necessary "machinery" to survive and reproduce on their own. Bacteria are many times larger than viruses. There are over 80 different types of pneumococci based on the different sugars that form their outer coating or capsule. These different types of pneumococci are called serotypes. The capsule helps the pneumococcus to infect humans by allowing the pneumococcus to stick to cells lining the respiratory tract (for example, the nose, throat, and tubes leading to the lungs). The capsule also helps the pneumococcus to avoid being eaten by white blood cells, a process called phagocytosis. Pneumococci tend to grow in pairs and chains and are lancet or bullet shaped. Figure 2 is a greatly enlarged (20,000 times normal) three-dimensional view of pneumococci using a special high powered microscope called a scanning electron microscope. Pneumococci can also be stained with various dyes which allow them to be seen under a regular light microscope found in most microbiology laboratories. The same dyes are commonly used to stain and examine sputum (that is, coughed up phlegm) from patients with suspected pneumococcal pneumonia or spinal fluid from patients with suspected pneumococcal meningitis (Figure 3). A schematic diagram of the pneumococcus is shown in Figure 4. The inside of the pneumococcus is surrounded by three layers. The inner layer is called the cell membrane and the middle layer is called the cell wall. The cell wall is made up of sugar-like molecules which are linked together to form a mesh or sheet which gives the bacterium its shape. The pneumococcal capsule forms an additional third layer or envelope around the bacterium, protecting it from phagocytosis. The inside of the pneumococcus is called the cytoplasm. The cytoplasm contains water, salts, deoxyribose nucleic acid (DNA), ribose nucleic acid (RNA), various structures (ribosomes for example), proteins, enzymes, and other substances necessary for life.