Abscess
The body reacts to some invading germs by building a wall of tough fibrous material around the infected area. Large numbers of white blood cells then pass into the cavity to kill off the germs. A thick creamy fluid, pus, is formed from the dead white cells and germs. The pressure inside this abscess builds up until it either bursts or is lanced by a doctor. Once the pus has been let out, the acute inflammation subsides and finally heals over, leaving a scar.