(1) caseous pneumonia has a history of tuberculosis and its onset is slow. Tuberculosis can be found in sputum with normal white blood cell count. X-ray examination shows that there may be a cavity in the lung.

(2) The secondary infection of lung cancer is older, and the symptoms of chronic poisoning are not obvious. X-ray examination and fiberoptic bronchoscopy with blood in sputum can continue or assist diagnosis.

(3) Acute lung abscess is often accompanied by a lot of pus and phlegm. X-ray examination shows that the cavities on the liquid surface can be distinguished.