In "The Last Leaf," the author describes pneumonia as a cold stranger with equally cold hands. He personifies the sickness as a malevolent character called Mr. Pneumonia.
Accordingly, Mr. Pneumonia is also invisible; no one can see him. He infects many people on the east side of Greenwich Village. However, he seems to slow down once he gets to Greenwich Village. Nevertheless, Mr. Pneumonia decides to infect Johnsy, said to be a diminutive little woman from California. All things considered, the author describes pneumonia as an invisible, malignant character who stalks the weak and innocent and consigns them to a miserable death.
After Mr. Pneumonia touches Johnsy with his cold fingers, she becomes bedridden. Johnsy loses her will to live, and the doctor tells her roommate Sue that there is little hope for someone who chooses not to fight the illness.
In the story, Mr. Pneumonia also infects old Mr. Behrman, the painter. Because of his compassion, Mr. Behrman decides to help Johnsy live. During the night, he paints the last leaf on the old tree. It is his best work, a masterpiece. The leaf is so realistic that it comforts Johnsy immensely.
It also convinces her to hold on to life. Basically, Mr. Behrman sacrificed his health and life in order to save Johnsy. The next day, Mr. Behrman dies. Although Mr. Behrman succumbs to pneumonia, his sacrifice has helped preserve a young life.