The CAMP test involves a bacterium that produces a ß-lysin (beta-lysin), which partially lyses, or destroys the red blood cells (RBCs) in the medium, which in this case is Staphylococcus aureus, i.e. the central vertical streak. The plate is then inoculated with test subject bacteria, which in this case was Arcanobacterium haemolyticum, formerly Corynebacterium haemolyticum (upper horizontal streak), and Arcanobacterium pyogenes, formerly Corynebacterium pyogenes (lower horizontal streak). Note that these streaks do not touch the central S. aureus streak.