Nineteenth-century breakthroughs in genetic science led to a growing interest in inherited disease and traits. A Doll's House contains several references to the idea that both physical disease and moral traits are passed down through generations. Torvald, after he reads Krogstad's first letter and rejects Nora, forbids her from bringing up their children as he thinks she will taint them morally. She herself is already convinced of this and has begun to distance herself from them. Torvald believes that Krogstad's children will be poisoned by their father's moral crimes. Dr Rank has inherited tuberculosis of the spine, the disease that kills him, from his father, who led a promiscuous life and contracted venereal disease.