The fibrogenic effects of mineral dusts injected into the pleural cavity of mice.

A series of mineral dusts were injected into the pleural cavities of mice in order to test their relative fibrogenicity. It was found that long fibre dust specimens produced widespread cellular granulomata which formed firm adhesions between the lungs, diaphragm and chest wall. These granulomata were gradually replaced by fibrous tissue and in old animals the dust was often found embedded in masses of acellular collagen. When the same mineral samples were more finely ground and sieved so that no long fibres remained in the dust, the resulting granulomata were much smaller and did not form adhesions. The small granulomata did, however, fibrose eventually and the dust was embedded in small nodules of collagen. Non-fibrous mineral rocks when finely ground and sieved also produced small non-adherent granulomata. The actual size of these granulomata depended on the number of cells attracted to the dust and this did vary with the different samples tested. The final degree of fibrosis within the granulomata was very closely correlated with the initial cellularity of the lesions. Those that were very cellular produced considerable amounts of collagen while little was produced if the initial granulomata had contained few cells.