Pneumonokoniosis is a condition of the lung characterized by the presence of dust particles of various kinds. When the fine particles gain entrance, they cause a catarrhal inflammation of the alveoli. Much of the dust may be expectorated, but some penetrates the interlobular connective tissue, where it may remain or be carried to the lymph-nodes. By acting purely as a mechanical irritant, or particularly if the particles are not aseptic, a productive inflammation with the formation of fibrous tissue results. This occurs in both lung and lymphatic tissue.

Fig. 142. - Lobular Pneumonia (Aspiration). X 8 (Ziegler). a, Pleura; b, lung; c, pneumonic areas; d, bronchiole; e, blood-vessels.

Some of the foreign particles may get as far as the lymph-nodes in the fissure of the liver, and through involvement of a vein the dust can gain entrance into the circulation and be deposited in the liver and intestine.

From the irritation a lobular pneumonia may occur and even cavities (non-tuberculous) form. There is always found at post-mortem some dust inhalation, the amount depending upon the environment of the individual.

According to the kind of particles inhaled, the condition receives various names: Anthracosis, when coal-dust; siderosis, metal dust; chalicosis, stone dust.

Secondary fibrous pneumonia results from an overgrowth of the connective tissue of the septa, which become much thickened. There is also proliferation involving the alveolar exudate.

The pleurogenic form of fibrous pneumonia results from chronic pleurisy. The lung shows numerous large and thickened trabecular of fibrous tissue extending from the surface deep into the interior of the organ.

Fig. 143. - -Catarrhal Pneumonia, showing Desquamated Epithelial Cells in the Alveolar Spaces (McFarland).

The peribronchial and perivascular forms present an overgrowth of connective tissue in varying degrees, about the bronchi and vessels. A moderate form of this is found in all the varieties of fibrous pneumonia. - Pleurogenic pneumonia is a form that has its origin in an inflammation of the pleura. Involvement takes place not only by contiguity but by extension into the deeper portions of the lung by way of the lymphatics - purulent lymphangitis. Abscesses of the lung may be caused in the same way by an extension of an empyema. The lobules of the lung may be separated by bands of suppurating tissue (dissecting pneumonia). There is thickening of the surface of the lung and of the pleura due to an extensive round-cell infiltration.