The anatomy of the lungs is like that of an upside-down tree. The tracheobronchial tubes are the trunk and branches, and the alveoli are the leaves. As shown in the diagram, the alveoli are like bunches of grapes, which are hollow grapes. The skin of the grapes is covered with blood vessels, which are filled with air. The contact between the blood vessels and the air occurs by spitting out the old and the new, and the blood takes away the oxygen and leaves behind the carbon dioxide. Pneumonia is when microorganisms (bacteria, viruses, atypical pathogens, fungi, protozoa), etc. multiply in the alveoli and destroy the structure and function of the alveoli. The severity of the disease varies depending on the extent of the damage. For small-scale pneumonia, outpatient treatment is sufficient, while extensive ones require hospitalization. In addition to fever, cough, sputum, fatigue and weakness, patients may have infiltrative shadows on chest CT and elevated white blood cell count and centriolar cell percentage on routine blood tests. There is a wet rhotic sound on auscultation. Treatment varies depending on the cause. Antimicrobials such as cephalosporins are commonly used for bacterial infections, and respiratory quinolones or macrolides are chosen for atypical pathogens. Pneumonia can have a mortality rate of up to 30% and therefore should not be taken lightly.