Hawthorne uses a striking scientific metaphor in describing Dr. Heidegger's eccentric nature as the "nucleus for a thousand fantastic stories":
Now Dr. Heidegger was a very strange old gentleman, whose eccentricity had become the nucleus for a thousand fantastic stories. Some of these fables, to my shame be it spoken, might possibly be traced back to my own veracious self; and if any passages of the present tale should startle the reader’s faith, I must be content to bear the stigma of a fiction monger.
A "nucleus" is the most basic, essential, or central "core" of something. Fittingly, given Dr. Heidegger's interest in the sciences, we most often use the word "nucleus" in scientific contexts: the "nucleus" at the center of a cell, or atom, or comet, for example. In describing Dr. Heidegger's eccentricity as the "nucleus for a thousand fantastic stories," Hawthorne imagines Dr. Heidegger as the centermost point of a wide plane of stories, gossip, and hearsay. Gossip, Hawthorne suggests, spreads outwards from some central point, extending further with each retelling like a game of "telephone" that radiates in all directions. The narrator, with some defensiveness, even acknowledges their own personal responsibility in spreading some of these "fables" regarding the doctor.
Hawthorne uses a striking metaphor in his outline of Colonel Killigrew's regret-filled life.
Colonel Killigrew had wasted his best years, and his health and substance, in the pursuit of sinful pleasures, which had given birth to a brood of pains, such as the gout, and divers other torments of soul and body.
The metaphorical idea that the Colonel's "sinful pleasures" have "given birth to a brood of pains" suggests that his hedonistic indulgences have led to nothing but trouble. The narrator does not delve into the specifics of the Colonel's "sinful" life, but the effects it has had on his health and psyche are clear. The Colonel is afflicted, for example, by gout, a painful disease traditionally associated with decadent food and drink like sweet desserts, fatty meats, and alcohol. This is just one of the "brood of pains" which to which the colonel's pursuit of pleasure has "given birth," a metaphor that suggests his lifestyle choices are responsible for producing the afflictions that torment him now.
This metaphor becomes particularly pointed in the context of 19th-century American social values: there was a strong expectation that a man of Colonel Killigrew's advanced age would be the head of a large family. Instead, as Hawthorne's metaphor of "birth" suggests, the colonel's only "brood" (or, in other words, children) are the problems he has brought upon himself as the result of his actions. Overall, then, Hawthorne's metaphor suggests that the colonel's "pursuit of sinful pleasures" has not only left him in poor health, but also without a family to bring him comfort.