330 SCIENCE PROGRESS 



hand, does not appear to have this effect, and unless breathed in very large 

 amounts is harmless, if not actually beneficial — coal miners in England have a 

 lower phthisis mortality than agricultural labourers. 



Many attempts have been made to explain the reasons for this difference, and 

 the popular idea, even among medical men, is that the deadliness of silica is due 

 to the hardness and sharpness of the particles. However, even coal particles are 

 often sharp and angular, and also are moderately hard. Further, it is found that, 

 if silica be inhaled mixed with coal-dust or with clay, it becomes relatively harm- 

 less, which would not occur if its harmfulness were due solely to hardness and 

 sharpness ; so a further explanation is necessary. Experiments have been carried 

 out by Prof. Beattie at Sheffield and by Drs. Haldane and Mavrogordato at Oxford. 

 Guinea-pigs were exposed to various kinds of dust, and after a certain time they 

 were killed and their lungs examined. In all cases the dust was found to be 

 present immediately after exposure, and was taken up by the epithelial cells of the 

 lung alveoli. In the case of silica these cells mostly remained in situ, and 

 eventually produced fibrosis ; but in the case of coal they became detached and 

 wandered out with their loads of dust (hence the " black spit " of coal miners), so 

 that the lungs of a guinea-pig exposed twelve months previously to coal-dust 

 appeared perfectly normal. That is to say, that coal and the other harmless dusts 

 have the power of stimulating the epithelial cells while silica is inert. This stimu- 

 lating power is probably due to adsorbed substances. 



It has been found that, if a mixture of silica and coal be inhaled, the mixed dust 

 enters the epithelial cells, as in the case of the unmixed dust ; the cells become 

 detached, as in the case of coal alone, and they wander out with their mixed load 

 of coal and silica. That is to say, that the dangerous silica is rendered harmless 

 by the addition of coal. This opens up a new method of dealing with dangerous 

 dusts. By means of water-sprays and ventilation in mines it is possible to greatly 

 reduce the dust. However, a small quantity remains which is still sufficient to do 

 damage to workmen constantly exposed. Probably it will be possible, by adding 

 coal to this remaining dust, to render it harmless, and just as stone-dusting is used 

 in coal mines to prevent coal-dust explosions, so coal-dusting will be used in quartz 

 mines to prevent miner's phthisis. 



The experiments at Oxford were interrupted by war work, but have now been 

 resumed in Dr. Haldane's laboratory at the expense of the Medical Research 

 Committee. Dr. Mavrogordato is shortly going to South Africa in an advisory 

 capacity, and during his absence the experiments are being carried on by the 

 writer. 



REFERENCES 



Beattie, Appendix to First Report of the Explosions in Mines Committee, H.M. 



Stationery Office, London, 1912. 

 Haldane, Trans, of the Institute of Mining Engineers, vol. lv, pt. iv, pp. 264-93, 



1918. 

 Mavrogordato, Journ. of Hygiene, vol. xvii, No. 4, October 1918. 



