Abstract
Fibrous quartz, chrysotile asbestos, and tremolite talc dust, all of respirable particle size, injected intratracheally, produced polypoid proliferative inflammations within smaller air-conducting tubes as well as more peripherally. With time, the inflammatory tissue became converted into coUagenous scars which often caused permanent deformities of bronchi and bronchioles. After intratracheal injection of a fibrous dust such as synthetic chrysotile, ceramic aluminum silicate, silicon carbide, glass, or brucite, the main pulmonary response was a macrophage reaction with minimal stromal participation. In addition, within 4 days after the injection, there were foci of polypoid proliferative inflammation but limited to the more peripheral respiratory bronchiole and alveolar ducts. Because these polypoid lesions did not collagenize and did not destroy the anatomic integrity of the air spaces, and because the lesions were reversible, the dusts calling forth this type of response must be classed as biologically “inert.” Furthermore, the polypoid lesions are believed to be artifactual in the sense that their production is determined by the method of introducing the dust into the lungs, since such lesions are not seen in animals inhaling high concentrations of the same dusts.