THE miners' phthisis OF THE RAND. I3I 



plains and justifies the conclusion that it is only fine siliceous 

 dust which is dangerous to the lungs. 



We have thus seen that the miners' phthisis of the Rand is 

 due primarily to the breathing of air carrying minute siliceous 

 particles, and secondarily to an infection of the damaged lung 

 b}^ the tubercle bacillus. It is therefore obvious that the sup- 

 pression of the disease will be obtained by action in two direc- 

 tions — preventing the workers from inhaling the dust, and 

 detecting and excluding from the mines all those who are expec- 

 torating the tubercle bacillus. 



I shall not make more than a brief reference to the principle 

 involved in the various precautions now adopted to prevent the 

 worker from breathing dust. 



Machine drills, the attendance on which has been such a 

 prolific cause of the disease amongst hard-rock miners both here 

 and in other countries, are now so constructed that they auto- 

 matically deliver water along a channel in the drill into the hole 

 which is being excavated ; the dust produced by the abrasion of 

 the rock is thus immediately converted into a very thin mud. A 

 further improvement in this type of machine would be a device 

 which could Ijc fixed around its neck to collect the water escaping 

 from the hole, and enable the machine to be used for drilling 

 overhead rock without inconveniencing the worker by the falling 

 mud. Such a device would probably take the form of a deep- 

 guttered tray, or funnel, fitted with a drainage tube to conduct 

 the slime into a bucket or other receptacle. 



Dryness of the underground workings, paradoxical as it 

 may appear, is inimical to health. Whilst the flinty powder, pro- 

 duced by drilling and blasting, is held in the form of mud or 

 slime, it is innocuous ; the danger arises when it is allowed to 

 dry on the hands, clothing, implements, or any other surface 

 which is liable to be disturbed. The past experience of the 

 pottery industry in this matter is very instructive. What 

 appeared to be one of the most potent causes of potters' rot, in 

 the past, was the handling of the dry biscuit ware, from the sur- 

 face of w^iich a fine siliceous dust was liberated when it was 

 touched with the hands. As the biscuit ware could not, of 

 course, be wetted, this particular source of danger has been re- 

 moved by the aid of powerful extraction fans. 



Blasting is an operation which inevitably liberates a large 

 amount of dust, mainly, of course, from the shattered rock, but 

 partly from dust-covered surfaces which have been allowed to 

 become dry, and which are disturbed by the concussion. The 

 amount of dust liberated into the air of the underground work- 

 ings by blasting is greatly reduced by the use of water-blasts, 

 sprays, atomisers, water-screens, and other devices. Despite 

 all such expedients, however, a fine, impalpable, and often in- 

 visible dust hangs in the air for several hours afterwards. The 

 worker can be prevented from inhaling such air either by secur- 



