128 THE miners' phthisis of the rand. 



plants, it is not an original component of the bodies of the higher 

 animals. The lungs of an infant do not contain any silica, but 

 as life advances the amount of this extraneous material gradually 

 increases, and by the time adult life has been reached it forms 

 from lo to 15 per cent, of the ash. In contrast with this figure 

 the analyses of Dr. J. McCrae show that the ash of a miner's 

 phthisis lung yields from 30 to 50 per cent, of silex. 



Anyone who engages in a dusty occupation is liable to the 

 accumulation of minute particles of foreign matter in the tissues 

 of the lung, and to this condition the generic name of pneumono- 

 koniosis is applied. Special names are given to the condition 

 when it is due to particular varieties of dust : thus particles of 

 iron and iron oxide give rise to siderosis ; if the dust be that of 

 coal, the condition is one of anthracosis ; clay dust produces 

 aluminosis, and dust which is mainly composed of siliceous par- 

 ticles is responsible for silicosis. 



It is a noteworthy fact that, contrary to popular belief, most 

 varieties of dust, even of mineral dusts, are not acutely harm- 

 ful. Careful enquiries have shown that there is no industrial 

 phthisis amongst operatives who habitually inhale the dust from 

 coal, chalk, plaster of Paris, bricks, tiles, emerv, slag-wool, glass, 

 and Portland cement. The dust which, before all others, 

 possesses power for evil is the one to which we have already 

 referred, 7'ic.. siliceous dust. It is siliceous dust (the particles 

 being of silica and not silicate) which is responsible for that in- 

 dustrial disease which a])])ears in different industries under such 

 names as grinders' rot. potters' rot. stonemasons' rot, and miners' 

 phthisis. 



Tt was formerly thought that needle-grinders and fiour- 

 millers developed their phthisis in consequence of inhaling par- 

 ticles of steel and flour respectively ; it is now known, however, 

 that the grindstone, and not the material ground, is responsible 

 for the trouble. The old-fashioned p-rindstone is made of 

 French buhrstone, millstone grit, or other very hard sandstone, 

 and it is the refacing of the grindstone or the running of it in a 

 drv condition which has. in the past, been so prolific a cause of 

 industrial phthisis. 



Flint is practically pure silica, and it is the use of finely 

 ground flints in the ceramic industries which has been responsible 

 for the phthisis death-rate in the potteries. 



Granite contains about 30 per cent, of silica, and the harder 

 varieties of sandstone contain much more; it is amongst the men 

 who cut such hard siliceous stone that stonemasons' rot is pre- 

 valent. Marble-workers and cutters of limestone no not appear 

 to be materially more liable to phthisis than other peoeple. 



Quartz is pure silica, and the dust which is primarily re- 

 sponsible for the production of gold-miners' phthisis is that 

 which is derived from quartz, and the siliceous rock known as 

 quartzite. 



An interesting confirmation of the specifically injurious in- 



