The Effects of the Inhalation of Coal and Stone Dusts on the Lungs of Pit Ponies

The inhalation of coal and stone dust, as used in collieries, by pit ponies produces no permanent lesions of the lungs. The dusts accumulated in the lung continue to increase during the first two years of exposure (approximately), but the rate of elimination then becomes equal to that of absorption. The dusts accumulate, probably in the lymphatics, firstly around the blood vessels, secondly around the bronchi, and thirdly in the deep layers of the pleura. The dusts accumulate in greater amount around the smaller blood vessels and bronchi than around the larger ones. There is a greater deposition of dust near the pleura than deeper in the lung substance. The dust is eliminated via the bronchi and the lymphatics. Dust accumulates in the lymph glands and spleen. In the former, at least, it is largely intracellular. Excessive stone-dusting causes extra accumulation of dust within the lung: this, however, causes no fibrosis. All forms of the soft pit stone used were equally harmless. The normal horse's lung contains very little dust.