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Principle of Physical Disector. Electron micrographs showing sets of two parallel sections (~100 nm thick) of an alveolar epithelial type II cell. Three lamellar bodies (arrowheads), which only occur in the sampling section, were counted as well as one lamellar body (arrow) seen in the reference section, because the principle of bidirectional counting was applied. Nucleus (N), nucleolus (Nu), lamellar body (Lb), capillary (Ca).
