Haematite pneumoconiosis in Cumberland miners.

Iron oxide occurs as a dust in many industries apart from iron-ore mining. It is found in silver polishing, electric welding, and boiler scaling, as well as in the more obvious metal grinding, fettling, and blast furnace working where it may be mixed with varying amounts of silica. Some still consider iron oxide a harmless dust (Baldi, 1952) while others think that, like coal, it can produce changes in the lung substance even in the absence of silica. Kettle (1932) observed that if he covered quartz with iron oxide little or no fibrosis occurred and animals inoculated with ferric oxide developed no fibrosis. In 1933 I found that if ferric oxide alone was injected into guinea-pigs and rabbits localized dust aggregates appeared but no progressive fibrosis, When the experiment was repeated with itoir-oe contiining' 10% silica, even with the addition of dead tubercle bacilli, progressive massive fibrosis could not be produced, and as time passed the dust was transferred to the hilar glands Originally siderosis was considered to be a mixe dust pneumoconiosis, since the "knife grinder's lung " was the result of a combination of sandstone and ferric oxide. When the natural sandstones were replaced by carborundum and aloxan wheels it was thought that the problem was solved, but even the use of a silicon-free abrasive wheel and a silica-free parting powder did not prevent the disease, for in metal grinding and fettling there is still a considerable amount of silica attached to the casting in the moulding sand (McLaughlin, 1953). A purer form of siderosis is seen in silver polishers where jewellers' rouge (pure ferric oxide) is used as an abrasive, and for long it has been considered harmless, though radiographs indicate a considerable retention of the dust in the lungs (McLaughlin and Harding, 1956). The abnormality of the radiological picture caused by the radio-opacity of the dust was not thought to be associated with any change in the