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It has been tried in this study to produce chronic obstructive bronchitis in dogs by exposing them to high concentrations of SO2. The study was extended to 175 days and during that period the animals were exposed to 300-500 ppm SO2 for a total of 435 h. None of the three dogs developed serious respiratory damage. Most of the symptoms were transitory. Histological examinations showed increased number of goblet cells in trachea, main- and lobar bronchi and a slight alteration of the bronchial glands.

Inhalation of papain by dogs produced morphological changes corresponding to a centrolobular emphysema. The papain inhalation also induced a purulent catarrhal bronchitis. However, the functional changes seen in chronic obstructive bronchitis were not observed. During papain inhalation an increased sensitivity of the bronchial systems develops corresponding to a tremendous increase in bronchospasm in response to Acetylcholine aerosol. The parenchymal lung tissue in dogs is more vulnerable in developing emphysema after papain exposure than is teh bronchial system in developing a chronic obstructive airway disease.

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