1182 THE COLLIERY GUARDIAN. December 10, 1915. through having met with many cases in another district where the workings were in quartz. Similarly, at quarries in North Wales and Leicestershire where hard stone containing 70 per cent, or more of silica is obtained for setts, and is also ground up, no ill-effects were definitely known to result from breathing the dust. Special enquiries were made on this subject by the members of the Royal Commission on Metalliferous Mines and Quarries, including myself. Enquiries as to any connection between phthisis and the inhalation of slate dust had also a negative result. Not much light on the reason why some kinds of dust are so dangerous has been obtained as yet from a study of the dust particles found in the lungs after death. Large quantities of fine amorphous-looking dust can be seen, with the microscope, in the lungs of men who have been exposed to dust, and have died of lung disease; and whether the dust has been harmless or not, it may remain in the lungs for many years. For instance, in a case recently examined by Mr. Mavrogordato and myself harmless haematite dust, easily recognised by its red colour, was abundantly present in the lungs of a miner who died of typical fibrotic miners’ phthisis, due undoubtedly to work in Transvaal mines, although it was 13 years since he had worked in a haematite mine, and eight years since he left gold mining for another occupation in which he was never exposed to dust. He had worked in haematite mines after his first period of work in the Transvaal, and this may have had to do with the fact that so much haematite dust remained in his lungs. The physical and chemical properties of quartz strongly suggest that the production of phthisis as a consequence of inhaling dust is connected with the hardness, sharpness, fineness, and insolubility of the dust particles; but in the present state of knowledge this can only be regarded as a probable working hypothesis. The main fact definitely known is that as a consequence of the damage produced by continued inhalation of crystal- line siliceous dust of certain kinds, the lungs become predisposed to attacks by tubercle bacilli, the effects of which constitute phthisis, and also to bronchitis. It is very generally believed that a fibrotic condition of the lung may be produced by the influence of dust, apart altogether from infection by the tubercle bacillus. Animal experiments have, moreover, proved that intense exposure to dust will produce fibrosis, apart from tubercular infection; but though fibrosis (the practical conversion of the lung tissue into fibrous tissue) is com- monly far more prominent in cases of miners’ phthisis than in ordinary phthisis, the history of the cases I have seen has seemed to point to tubercular infection as a main cause of the final fibrosis and other serious symptoms. In the great majority of a number of cases examined by Prof. Ritchie and myself in Cornwall,* the tubercle bacillus was found by Prof. Ritchie in the sample of sputum examined. In the case of the former haematite miner referred to above, the lungs were typically fibrotic, and were free from cavities or caseous deposits, but the tubercle bacillus had been recognised in the sputum during sanatorium treatment 1J years before death occurred. In the solidly fibrosed areas visible dust was, moreover, scarce—a fact which seemed to be against the theory that dust alone was the direct cause of the main fibrosis. Harmless Nature of Shale Dust. The variety of inert dust originally proposed by Sir William Garforth for preventing coal dust explosions was the dust of powdered shale. This dust is naturally present on the roads of most British coal mines, and was present in large amounts on many of the roads at Al tofts, the colliery under his control. Most of the experiments on inert dust at the Eskmeals Station have been made with shale dust. I shall first deal, therefore, with the evidence as to the effects of shale dust inhala- tion. On this point there is fortunately very satisfactory evidence from actual experience in coal mines, backed by the results of experiments on animals. In proposing the use of shale dust, Sir William Garforth was well aware that the presence of dust from shale or “ bind ” was no new factor in coal mining. A great proportion of the roads at Altofts Colliery (includ- ing those in which inflammation was arrested in the Altofts explosion of 1886) and other collieries are and always have been thickly covered with shale dust. This is especially the case with return roads, which in this district commonly include the travelling roads. When a shift is going in or coming out on one of these travelling roads, much shale dust is raised into the air, and the men necessarily inhale a good deal of shale dust. Through the courtesy of Sir William Garforth and Mr. Lloyd, general manager of Altofts Colliery, I was enabled to observe the amount of dust thus raised. No ill-effects attributable to the shale dust had ever been experienced so far as local enquiry could decide the question, and I, myself, personally interviewed a number of the older men who had been accustomed over long periods to travel in and out along return roads thick with shale dust. They were not only perfectly well and sound in health, but were unanimous in considering that the shale dust did no harm to them or to other men. In most collieries the men travel in and out on intake roads which are naturally covered, not with light- coloured stone dust, but with black dust, which would naturally be classed as coal dust. The men, of course, breathe a great deal of this dust when it is disturbed by the shift going in or coming out. A great deal of black dust must also be inhaled during work at the face or in haulage operations. Now this dust is, fortunately for safety from explosions, seldom pure coal dust, but a mixture of coal dust with dust from the shales, clays, “ binds ” or “ clunches,” which usually constitute the * Report to the Home Secretary on the Health of Cornish Miners. Parliamentary Paper, Cd. 2091, 1904, p. 19. floor, roof, and sides. This material readily disintegrates with the work and traffic, the dust so formed mixing with the coal dust. Unfortunately, our information is as yet very imper- fect as to the proportion of stone dust usually present along the roads of collieries in different districts and working different seams, but it seems clear enough that there is nearly always a good deal of shale dust present, but for which colliery explosions would be, to judge from the experiments at Altofts and Eskmeals, much more frequent, .and far more violent. Samples of fine “ coal dust ” from intake roads or from the face, collected by myself and others in different collieries, and analysed at the Doncaster Coal Owners’ Research Laboratory, have commonly contained from 15 to 60 per cent, of stone dust. It is this mixture which is mainly breathed by the men, and the fact that colliers are, as a class, so immune from phthisis is in itself good evidence that dust from the shales, etc., which are commonly adjacent to coal seams is relatively harmless. It is possible, however, to bring forward still more definite evidence, thanks to an investigation recently conducted under the direction of Mr. J. W. Fryar, general manager of Messrs. Barber, Walker and Com- pany’s collieries, and a member of the Doncaster Coal RELATIVE- DEATH RATES FROM LUNG DISEASE CM 6 O 2 o o CE ul 0 40 12 18- ,0^' 22 20 24 O u z 0 z o 8 u (0 5 Ct X ui a O z z bJ % UJ