The personification of pneumonia in The Last Leaf helps the reader trace the movement of the outbreak across the city, and establishes a sense of impending danger and narrative tension. Early on in the story, pneumonia is introduced almost as a character in its own right:
In November a cold, unseen stranger, whom the doctors called Pneumonia, stalked about the colony, touching one here and there with his icy finger.
Already, the use of the verb “stalking” lends a predatory nature to pneumonia’s transmission, and insinuates its lethality. During the time in which this story is set, there were no genuinely effective treatments for pneumonia; the mortality rate was high, and both the public and the medical establishment in the United States respected and feared the disease. The choice of menacing language to describe pneumonia not only reflects the author’s desire to cast the illness as a kind of villain in the story, but also the relationship American society had with the illness during this period.
Also, consider the use of “cold” to describe pneumonia, and how this is reflected in the language describing its transmission (“touching…with his icy finger”). Pneumonia is depicted as a frigid, threatening, and powerful figure, one who must merely touch someone with a finger to end his life. He seems to stalk slowly through the city without impediment or obstacle. The power pneumonia holds and the freedom with which he moves poses an existential threat to the denizens of Greenwich Village, giving the story a source of ongoing, recognizable tension. It is clear that pneumonia is on its way; when he will arrive and who he will take are impossible to say. The reader can be sure that it is unlikely anyone will be able to stop him; he holds the city in his caprice.