Mechanical damage to rabbit tracheal epithelium from inhaling inert pyrite dust of needle-like structure.  Part II. 
The ultrastructure of rabbit tracheal epithelium was studied 2, 8 and 26 hours after termination of 8-hour inhalation of ground pyrite dust.  Pyrite particles persist in the cytoplasm of ciliated cells throughout the interval followed up.  Only through degeneration and elimination of these cells from the epithelium is the inhaled dust gradually removed from the mucous membrane.  Goblet cells discharge pyrite-containing mucus into the ciliary border region for a period of 26 hours after cessation of inhalation thus inducing further damage to the ciliary border and the apical regions of the cells even after termination of inhalation.  The morphological appearance of the ciliary border, especially in the first phase after termination of inhalation, suggests a disturbance of the self-cleaning function of the eipithelium of respiratory passages.  The inhalation of aerosol of needle-like structure causes mechanical damage to tracheal epithelium.  Substantial retardation of the onset of epithelial regeneration and slow rate of elimination of the inhaled aerosol from the tracheal mucosa was noted.