Shmoop is pretty convinced that there's subtle imagery of illness running under "Paul's Case"—like maybe part of "Paul's Case" is that he's got the same illness that killed him mom. It's really subtle, but the subtle parts are the ones that make you feel smart. Check it out:
First, we learn that his mother "died out there of a long illness" (1.8). In this case, "out there" means Colorado, which is basically code for "had tuberculosis."
Some quick facts about tuberculosis: It killed a lot of people throughout history; it was thought to be hereditary (although it turned out to be contagious); and, in the nineteenth century, it was the most fashionable way to die because, not only did it show that you were totally romantic and too good for this world, it made you pretty: pale skin, bright eyes, and unnaturally flushed cheeks. Not to mention skinny.
Anyway, Paul doesn't have the coughing-blood-into-a-handkerchief symptom that usually gives the illness away in books and movies, but he does have a lot of other key symptoms: unnaturally bright eyes with a "glassy glitter" (1.2), a "white, blue-veined face," and an unhealthy looking set of "high, cramped shoulders and a narrow chest" (1.2). Not to mention that, when the music starts playing, his "cheeks and lips" flush (1). Oh, and there's also the fact that tuberculosis (or consumption, as it was called) was though to make its sufferers sensitive and nervous.
We're not saying that Paul actually has tuberculosis. By 1905, people understood that the disease was contagious, so Cather probably isn't trying to suggest that Paul inherited it from his mom and is actually dying. Rather, the imagery of illness probably suggests that Paul has some kind of other disease—a disease of the mind.