Any mucous-like material that is coughed up from the respiratory system is called sputum, and sputum that contains the tubercle bacilli is called positive sputum. It is by means of the positive sputum that tuberculosis is transmitted from one person to another. The finding of tubercle bacilli in the sputa was the most conclusive evidence doctors could obtain to confirm the diagnosis of tuberculosis. Sputum coughed up by a tuberculous patient is no different in appearance than sputum due to any other cause.