Using limited resources, the team at NASA needs to invent a way to fit a square cartridge into a round hole in order to create a CO2 filter. This filter would prevent the CO2 levels from rising too high in the spacecraft. Otherwise, the crew will face complications such as impaired judgment and blackouts.
The group escapes from hepatitis B and enters Alveoli Forest, where they encounter the bronchial tubes, alveoli, and the disease, tuberculosis. Dr. Bloom explains that the human has latent tuberculosis, as the disease is usually found in many people's lungs but is not active. He changes his opinion, however, when he sees that tuberculosis bacteria has escaped from its inactive state.
Red and White Blood Cell head to the bronchial tubes as part of White Blood Cell's plan to eliminate the pneumococcus. They head to the respiratory tract where mucus is formed and lure the bacterium to be sneezed out of the body.