The cultivation of strict anaerobic bacteria poses a special problem because these bacteria may be killed by exposure to air. Dissolved oxygen in the medium forms toxic free radicals and hydrogen peroxide in the presence of metabolic electrons. Obligate anaerobes are incapable of detoxifying these active forms of oxygen. To grow non stringent anaerobes on solid media, Atmosphere Generation Systems are used which release carbon dioxide. In the presence of a catalyst the oxygen is chemically bound and the oxygen will be removed from the jar. It is also possible to get completely anaerobic conditions by filling anaerobic chambers or jars with inert gases used for the cultivation of strict (obligate) anaerobes.