In order to test the silica theory of the origin of progressive massive fibrosis (P.M.F.) in coal-miners' pneumoconiosis, separate dust analyses have been made of the massive lesions and of the rest of the lung from 18 coal-workers with P.M.F. who had been employed in several coalfields. The dry weight of the massive lesions ranged from 5 to over 100 g. and the dust concentration in the P.M.F. lesions was on an average twice as high as in the rest of the lung. It was found that the quartz percentage of the lung dust was almost identical in the two samples from each lung (Table 3). The quartz content of the average lung dust (P.M.F. and “rest of lung”) of 32 cases of P.M.F. was compared with that of 58 cases of simple pneumoconiosis. The quartz content of the P.M.F. dust was slightly higher but, allowing for variable dust composition in different coalfields, the difference was not significant (Table 8). The silica theory of P.M.F. cannot be supported by this study.
Comparisons of the collagen content of the P.M.F. lesions and of the rest of the lung in 17 lungs and of lesions of P.M.F. and of simple pneumoconiosis in 31 and 27 lungs, respectively, showed no clear difference between any of the groups and surprisingly low values for the massive lesions. A possible way in which this result could be reconciled with the histopathological observations is suggested. One gram of coal-mine dust produced, on an average, 0·4 g. of dust produced between 2 and 7 g. of extra collagen.
extra collagen. In five silicotic lungs, where the lung dust contained 15 to 50% of free silica, 1 g. of dust produced between 2 and 7 g. of extra collagen.
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