Lungs of dogs were examined morphologically and histochemically after chronic inhalation of sulfur dioxide (SO2). The epithelial changes included squamous metaplasia, which was most prominent and diffuse in the proximal trachea and focal in the more distal respiratory tract. The metaplastic epithelium differed from normal oropharyngeal stratified squamous epithelium in its formation of sulfated mucosubstance. Mucous goblet cells were sparse and involuted in the surface epithelium of the distal trachea but showed marked hypertrophy and hyperplasia in a large portion of the epithelium of bronchi and bronchioles. The mucous goblet cell secretion, although increased in amount, disclosed moderately to markedly decreased periodic acid Schiff (PAS) reactivity and affinity for basic dyes. Ciliated cells and the surface layer of sulfated mucosubstance presumably derived from these cells were either diminished or absent in bronchi with goblet cell hyperplasia. This depletion correlated with accumulation of secretio...
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Spicer et al. (1974) studied this question.