Light (a) and electron (b–d) micrographs of pleural and pulmonary structures of inflating lungs of living mice, as prepared by the “in vivo cryotechnique ”. In the light micrograph (a), ballooning pulmonary alveoli (asterisks), structures of pleura (arrows) and flowing erythrocyte s (arrowheads) in septal blood capillaries are well preserved in functioning lungs of living mice. (b) An electron micrograph is showing the mesothelial cell (arrowheads) and alveolar septum (arrows). Asterisk, pulmonary alveolus. (c) In another alveolar septum, pulmonary alveoli (small asterisks) and blood capillaries (large asterisks) are closely associated with each other. R, erythrocytes . (d) In the septal blood capillaries, flowing erythrocytes (R) exhibit their various shapes instead of typical biconcave discoid shape s (inset), and some erythrocytes are firmly attached to endothelial cell s (arrowheads). The surfactant layer (arrows) is rarely preserved on the alveolar type I epithelial cell (AE). BM basement membrane , E endothelium . Bars, 1 μm