96 THE NEW PHYSIOLOGY. 



perience. Work on the health conditions at metalli- 

 ferous mines, quarries, and factories brought me into 

 contact with the terrible phthisis mortality which some- 

 times results from dust inhalation. The effect is mainly 

 due to siliceous dust, such as that from the Craigleith 

 sandstone formerly used in Edinburgh, or from millstone 

 grit, gannister, Transvaal quartzite, or the powdered 

 flint used for pottery . work. But in many industries 

 men are also greatly exposed to dust, and even dust 

 consisting largely of crystalline silica ; yet no excess of 

 respiratory trouble occurs among them. Coal-miners, for 

 instance, breathe much dust, and with it a great deal 

 of siliceous dust, but suffer even less from phthisis than 

 agricultural labourers ; and one finds men who have 

 worked for decades in very dusty crushing mills, where 

 extremely hard stone is crushed, containing 70 per cent, 

 or more of silica, and yet they show no signs of ill effects. 

 It seemed clear that much is hidden behind the name 

 " pneumoconiosis " ; but what ? Evidently the first 

 thing to do was to find out whether, and by what means, 

 the lungs get rid of a harmless dust, such as coal-dust 

 or shale-dust. The microscopic work was carried out 

 by Mr Mavrogordato at my laboratory, with the financial 

 support of the National Medical Research Committee, 

 and resulted in showing that though with ordinary ex- 

 posures the harmless dusts enter the lung alveoli in 

 large amounts, the dust is all got rid of after a certain 

 time. It is carried out by dust-collecting cells along 

 several paths. In the case of pure siliceous dust, how- 

 ever, the transport fails, or is very slow, though the dust 

 is collected in cells as before. The dust-containing cells 

 remain, therefore, in the walls of the lung alveoli and 



