In "The Last Leaf," pneumonia is personified as Mr. Pneumonia and described as a cold stranger and a "ravager" that has "stalked" over the country, touching people and infecting them with inflammation of the lungs at random.
When this cruel stranger arrives in November in New York City, he touches people at random, it seems. But on the east side of New York, "this ravager strode boldly, smiting his victims by scores" (score=20). Described with O. Henry's characteristic irony as less than a "chivalric old gentleman," Mr. Pneumonia strikes the small little Johnsy, whose blood is thinned from having lived all her life in California.
Poor Johnsy is overpowered by the cruel forces of the lung inflammation and weakened to the point that she begins to physically lose her hold on life, as well as her will to live. Her roommate and friend, Sue, urges her frail friend to fight for her life, but Johnsy begins to lose her will against the cruel Mr. Pneumonia. It is not until Sue elicits the aid of old Mr. Behrman that Johnsy is saved from the cruelty of the "ravager."