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Periodic acid fluorescent Schiff stain of a small airway from a patient with advanced emphysema. The entire airway is seen at ×10 magnification in A and a quadrant of the airway at ×40 in B. Mucin granules are shown in red along the apical border of the epithelium. Note the large intraluminal mucin plug (M) in A, also noted in B (white arrow). Reprinted by permission from Reference 120.
