In the next few days, Neville finds a microscope—and then, when he realizes his microscope is no good, a better one. Over the course of the next week, Neville becomes highly adept at using a microscope. One major obstacle to using the microscope is that the slides he finds at the library become covered with dust very quickly—there are dust storms in Los Angeles every four days or so.
Neville trains himself to be a competent scientist: he learns about using microscopes and slides. The fact that there are constant dust storms in Los Angeles suggests that the vampire disease is still present in the atmosphere (and that Neville’s immunity to the disease is again confirmed).
Neville obtains blood samples from vampires he encounters during his days. One day, he examines a blood slide under the microscope and identifies an unfamiliar bacterium: he concludes that this must be the “vampire germ,” and dubs it vampiris. Neville feels exhilarated with his discovery, but his exhilaration quickly gives way to despair. He wants to cure the vampire plague, but has no idea how to proceed.
Every one of Neville’s discoveries opens up a new set of questions. For example, his discovery of the vampiris bacterium immediately brings up the question of how to kill it. Neville has to force himself to be patient and steadfast: he must continue learning about vampires, instead of giving up and pouring himself a drink.
Neville tries to understand the vampiris germ. He knows that when a human being contracts the germ, they have to feed their bodies with fresh blood. If they run out of blood, they’ll eventually die: the vampiris gene will take over their bodies. Then, after the vampires’ bodies decompose, the vampiris gene will be swept to potential new hosts, thanks to the dust storms. Neville realizes that vampires are a historical reality. The bubonic plague, the plague of Athens, and other plagues of history were, quite possibly, the result of the vampiris germ. Neville also realizes that vampires, no less than “the living innocents who were originally afflicted,” are the victims of the vampiris germ.
Neville’s research into the causes of vampirism gives him a new moral perspective. Previously, Neville thought of vampires as vile monsters. Now, he realizes that, not only does vampirism have a scientific cause, but also that the vampires are themselves victims of the plague. Thus, it’s possible to feel sympathy for the vampires: they’re sick patients. However, even after he learns all this Neville will continue to kill vampires—rightly or wrongly, he believes that doing so is the only way to ensure his own survival.
In the evening, Neville continues thinking about the vampiris germ. He realizes that there are two different kinds of vampires. Some vampires originate from the corpses of human beings; these vampires are entirely controlled by their germs. Other vampires are physically alive, and have conscious minds; these vampires originate from living human beings who contract the vampire germ. Based on his experience, Neville assumes that the dead vampires can withstand bullets, though he doesn’t know how. Excitedly, Neville realizes that he hasn’t craved alcohol all day. He spends the night eating dinner and listening to records, and he manages “to forget all about vampires for a while.”
Neville’s scientific investigations provide a temporary “cure” for his depression and alcoholism. Instead of worrying about the impending threat of the vampires every night, Neville finds himself feeling genuinely excited about the future: he looks forward to learning more. Neville’s knowledge empowers him by proving that, contrary to legend, vampires aren’t supernatural, indestructible creatures—they’re just people with a bacterial disease.