How was the life of jonsy …

In "The Last Leaf," pneumonia is personified in different ways. First, O'Henry refers to pneumonia as "a cold, unseen stranger." This stranger "stalked" about Greenwich Village and laid his "icy fingers" on his victims. The disease is also compared to a "ravager." O'Henry also says that pneumonia is not chivalrous because he attacks a little woman, meaning Johnsy. Pneumonia is also called "the red-fisted, short-breathed old duffer." 

These images make the reader call to mind a ruthless and revolting old man who wheezes, who is cold at heart, and who has fingers made of ice. By personifying the disease, O'Henry makes Johnsy's opponent seem real and makes the reader want to rally behind Johnsy in her fight against pneumonia. It is only hope and faith that will be able to help Johnsy defeat this enemy, and until she has something to believe in (which turns out to be the last leaf clinging to the ivy vine on the brick wall outside her window), she can't begin to defeat her opponent, pneumonia.