Representative pictures of bronchioles. The number of BrdU-positive cells (intensive dark staining) in fluensulfone- and isoniazid-treated animals is increased compared with control on day 3, returning to base level after treatment with either substance on day 7. (A) Control, (B) Fluensulfone (day 3), (C) Isoniazid (day 3), and (D) Fluensulfone (day 7).