Effects of Cl2 exposure on lung histology. A: Normal mouse lung showing a large airway in cross section, an accompanying artery and two terminal bronchioles (Tb) that open into their respective alveolar ducts. B: Lung histology 12 h after a single 800 ppm Cl2 exposure. Partial or complete detachment of airway epithelium, as seen in this example, occurred in all airways. C: 10 d post-exposure, the epithelium is reconstituted and the airway wall is thickened. D: 10 d post-exposure, high magnification detail showing fully reconstituted airway epithelium. Stain: H&E. Scale bars: 100 μm in A-C; 25 μm in D.