The stereoscanning electron microscopy and ultrastructural histochemistry of the avian and reptilian surfactant systems: Indian dove, desert spiny and Taiwan golden skink lizards.

Lung tissues from the Indian dove, Scardafella inca, desert spiny lizard, Sceloporus magister, and the Taiwan golden skink lizard, Mabuya aurates, were studied by transmission electron microscopy utilizing ruthenium red as a carbohydrate stain and with the so-called lipid-carbohydrate retention procedures to elucidate the morphology of the surfactant systems. Stereoscopic scanning electron microscopic procedures were utilized for a comparative anatomical study of these three species, and the results were compared with the rat and frog in the companion article. The avian lung tissues demonstrated several perculiarities. The ciliated epithelial cells of the bronchus had cytoplasmic ciliated projections between the boundaries of mucus secreting cells. The discrete morphology of the main bronchus, secondary bronchi, parabronchi, and the air capillaries, and their three-dimensional morphologic perspective were elucidated. The skink illustrated an arrangement of primary, secondary, and tertiary septa, with elaborate tertiary septal pits, similar to the amphibian. All septa contained a solid connective tissue core. The desert lizard was similar to the skink except the tertiary septal pits were rudimentary. All three species had a modified great alveolar pneumocyte and a laminated surfactant which included a carbohydrate matrix material between layered phospholipid-based membranes. The ruthenium red additionally stained the homogeneous surface-lining material. A comparative analysis of the surfactant systems of these three species with each other, and with the rodent and amphibian in the companion article, were discussed in terms of phylogenetic origin.