What does the protagonist of "Blood" believe may drive his actions? How does he go about assuaging this need?

Once the protagonist is temporarily sated, he convinces himself that he was motivated by a lack of iron. He almost buys some, but the pharmacist wants to see a physician's prescription. Ashamed of himself, but unable to deny the growing need, he satisfies himself with raw chicken, which leaves him sick and retching for some time afterward.