The calcification of fibrous pleural lesions produced in guinea-pigs by the injection of chrysotile asbestos dust.

In guinea-pig pleural granulomas produced by the injection of chrysotile asbestos dust, the initial cellular lesions were replaced by old acellular fibrous tissue within 15-18 months. After this period calcification of the fibrous tissue commonly occurred. The first sign of calcification was always the formation among the collagen fibres of large numbers of spherical lamellated bodies. These structures stained positive for acid mucopolysaccharides, and electron-microscope observations showed that they were formed around a core of asbestos dust. Calcium in the form of apatite crystals was also often present in these structures. Shortly after the formation of lamellar bodies the mucopolysaccharide normally present on the collagen fibres, was removed and instead it formed a thick coating around any free asbestos dust in the fibrous area. The first signs of general calcium deposition were seen both in contact with collagen fibres and on the surface of the coated asbestos dust. Eventually calcium deposits filled all the tissue spaces and enclosed collagen, coated asbestos dust and lamellar bodies in a solid mass of calcification.