In this passage Torvald talks about the evil of lying of wrongdoing, and compares it to a disease of a sort. This is an fairly accurate description, both in how it degenerates the original person into a much harder hole to get out of, and spreading to other people by the person's examples. Nora takes this in a literal sense, suggesting a bit of un-education, which would probably be the case for a women in the 1800s. There's a good deal of dramatic irony and possibly a little situational irony in this section, as Torvald constantly says how he despises such people and that they make him physically ill, yet we know his wife -the person closest in his life, living with him, even the closest person in proximity to him at the moment- had committed such a crime with no ill effects on his behalf, even after a long period of time. Such demonstrates a sort of placebo effect in that symptoms will only come about only if he believes they will come about, which he expects to because of his determination that lying is wrong, therefore should cause other negative qualities too, including physical ailments.He also places a big emphasis of the effect on children around such a situation. Going with his poison metaphor, they would indeed be more likely influenced by their parents actions, not having the time and experience to know much else, and be less stringent on the laws in their adult life.