Increased airspace size in mice with tobacco toxin (TT) exposure during lung development compared to tobacco-naïve (NS) mice. A. Representative section of lung tissue stained with hematoxylin and eosin (H&E) from postnatal day 14 (P14) NS mouse (Magnification, 20X) showing normal alveolar size. B. H&E stain of representative section of lung tissue from P14 TT mouse (Magnification, 20X) showing enlarged airspace size, consistent with alveolarization defect. C. The mean linear intercept, which reflects average distance between gas exchange elements, is significantly larger in TT mice compared to NS mice. Data comparison performed using Student’s t-test. Abbreviation: N = number of mice in group. Data are mean ± SEM.