Agar plates are inoculated and placed in the jar. Water is added to the GasPak generator envelope, causing the evolution of H2 and CO2. he hydrogen reacts with oxygen on the surface of the palladium catalyst, forming water and establishing anaerobic conditions. Carbon dioxide aids growth of the anaerobes. An anaerobic indicator strip (a pad saturated with methylene blue solution) changes from blue to colorless in the absence of oxygen.