The invention of an instrument called the optical microscope and the new possibilities it offered to observe living material must be considered a major milestone in the advance of our understanding of the mechanisms of life. Huge numbers of important observations have been made using this instrument, but unfortunately it only produces two-dimensional images. The advent of the electron microscope, first the transmission electron microscope (TEM) and then the scanning electron microscope (SEM), then made it possible to observe the three-dimensional structure of specimens literally adding a whole new dimension to our understanding and bringing about a second major milestone in microscopy. With their highly specific architecture and great functional significance, the respiratory apparatus and the airways have received particular attention, and extensive series of investigations with SEM have been done. "To see is to understand", and many lung SEM investigations with different aims have been performed, but "to see again is to understand better", so we offer this collection of scanning electron micrographs, which, along with some familiar aspects, also presents new and unusual images of pulmonary morphology. We have noticed that although most pulmonary structures have already been seen, every time we scan a new specimen, new perspectives, new aspects, and new details emerge. We hope that physicians and scientists looking at these scanning electron micrographs will, just as we did, find new sources of wonder, and will then desire to delve deeper.

The invention of an instrument called the optical microscope and the new possibilities it offered to observe living material must be considered a major milestone in the advance of our understanding of the mechanisms of life. Huge numbers of important observations have been made using this instrument, but unfortunately it only produces two-dimensional images. The advent of the electron microscope, first the transmission electron microscope (TEM) and then the scanning electron microscope (SEM), then made it possible to observe the three-dimensional structure of specimens literally adding a whole new dimension to our understanding and bringing about a second major milestone in microscopy. With their highly specific architecture and great functional significance, the respiratory apparatus and the airways have received particular attention, and extensive series of investigations with SEM have been done. "To see is to understand", and many lung SEM investigations with different aims have been performed, but "to see again is to understand better", so we offer this collection of scanning electron micrographs, which, along with some familiar aspects, also presents new and unusual images of pulmonary morphology. We have noticed that although most pulmonary structures have already been seen, every time we scan a new specimen, new perspectives, new aspects, and new details emerge. We hope that physicians and scientists looking at these scanning electron micrographs will, just as we did, find new sources of wonder, and will then desire to delve deeper.