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JAMA. 1939;112(7):610-614. doi:10.1001/jama.1939.02800070026006.
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When attention became centered on silicon dioxide as the cause of fibrosis in silicosis, it was expected that a chemical analysis for the substance would establish the presence or absence of pathologic levels in tissues and body fluids. Work in this direction was carried out by King and his associates,1 Fowweather,2 Riddell,3 Boehme4 and McNally.5 As with many similar situations in science, the results obtained by these workers did not measure up to expectations, for a positive correlation between the quantity of silica and the extent of pathologic changes was found not to exist in many instances. A chemical analysis gives only total silica, which may occur in the tissue as free silica or in the combined form of some silicate. If silicates are present to any great extent, a high value for silica will be obtained. If at the same time the amount of


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