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Silicosis has been intensively studied since it was isolated from other diseases caused by dust. These studies have shown that silicosis may be fairly advanced without seriously impairing general health; it may, however, itself lead to a fatal result. More often it acts almost specifically in preparing the way for pulmonary infections, of which serious tuberculosis is the chief. The occurrence of such a superadded infection not infrequently precipitates a latent condition of silicosis. The close relation existing clinically between tuberculosis and silicosis has been demonstrated by animal experiment.
Other dusts than silica have also been demonstrated to cause generalized pulmonary fibrosis, which is usually finer in character, although more injurious to the functions of the lungs than is silicosis; but such fibrosis has not been found to be specifically associated with superadded tuberculous infection.
Each dust calls for special study. Up to the present, investigation of dusts from certain silicates has shown them to be of great importance. Of these, asbestos has been found to be most definitely injurious, and to originate a definite and characteristic condition. Other silicates, such as basalt, appear to set up a condition which only differs in degree from that caused by asbestos.
Dust arising from pure coal does not appear to be injurious, or, on the other hand, to be in any way protective against infections. Raw coal, however, often contains sufficient minerals for its dust to originate pulmonary fibrosis. When such fibrosis is present, whether due to silica arising from intervening rocks or from silicates, the coal particles are so retained in the lungs as to block the lymph passages, and impair capacity.
Certain other dusts, for example dusts arising from marble or limestone, exert little, if any, influence on the lungs. Such dusts are soluble in the body fluids, and are not left to block the pulmonary tissues.