In Edgar Allan Poe's "The Fall of the House of Usher," both the mansion and the family line of the Ushers have degenerated to the point that they can no longer sustain themselves. After so long, when people do not expand their gene pools, the genetic code becomes deficient. Such is the case with Roderick and his sister. She has an odd condition that causes her to become paralyzed--"Partially cataleptic"--and he complains of oversensitivity to noises and "nervous agitation." The narrator describes Roderick's art, readeings and playing of the guitar as having "an excited and highly distempered ideality [that] threw a sulfureous luster over all." Like the Usher house that has a "fissure, which, extending from the roof of the buiding in fron made its way down the wall...," the Usher siblings are somewhat deranged, physically aberrant, and jaded by their thin blood lines which have weakened by their geneology:
All time-honored as it was, had put forth, at no period, any enduring branch; in other words, that the entire family lay in the direct line of descent, and had always, with very trifling and very temporary variation, so lain.
Like Madeleine Usher's "emaciated frame" and Roderick's "nervous affection," the fissure in the House of Usher "widened" and the once "mighty walls" give way to destruction. Thus, the House of Usher may be interpreted as a metaphor for the family line of the Usher family.
Read as an allegory, Poe's story may be read as a figurative journey into the human mind. In fact, Poe himself said that the poem "The Haunted Palace" is meant to suggest a disordered brain." For instance, in Stanza V, Roderick's state of mind appears to be deteriorating as he speaks of "evil things, in robes of sorrow/Assailed the monarch's high estae." He feels that there is a foreboding presence surrounding his ancestral home that threatens him and his sister. And, in the final stanza, the "hideous throng [that] rush out forever" may be the ghosts of his ancestors who flee the house. Believing that all living and nonliving things are sentient, Roderick perceives all his environment as endangering his family and as acting in complicity in their demise.