La Peau de chagrin
In a letter written to Madame Hanska in 1834, Balzac decided to reorganize his works into three larger groups, allowing him (1) to integrate his "La physiologie du mariage" into the ensemble and (2) to separate his most fantastic or metaphysical stories — like "La Peau de chagrin" (1831) and "Louis Lambert" (1832) — into their own "philosophical" section. The three sections were: