The non-specific inflammatory response can be described as follows:

Once an injury to surrounding cells occur, mast cells and basophils (not shown) release histamines (also not shown) that attract neutrophils and cause vasodilation of the blood vessels closest to the injury. Neutrophils are the fastest to arrive and engulf the bacteria through phagocytosis. Some plasma containing small blood vessels and additional phagocytes will leak into the area surrounding the injury. Prostaglandins are also released, and these cause more dilation of the blood vessels. It also induces edema, or swelling, which explains why swelling occurs after an injury.

An intersting thing about pus: pus contains dead phagocytes and some plasma. Usually, the body will reabsorb pus within a few days of injury. However, sometimes it is released in other... methods.