To a modern eye, the language used in eugenic sterilization legislation can seem both puzzling and offensive. Here I would like to attend to the puzzle side of things and explore what explanation there is for the various traits and conditions that find their way into such legislation. These include mental deficiency, feeble-mindedness, Huntington's chorea, neurosyphylis, epilepsy, and tuberculosis. Some of the consistency and variation here surely, one might think, has a genealogical explanation. Yet there is more to a full explanation here than finding some putative ur-list of traits and conditions and tracing their descent.