1911.] The Causes and Prevention of Miners' Nystagmus. 25 



assumes this position, in my opinion, to bring his eyes into a relative 

 position of depression and convergence (the position of maximum stability), 

 and at the same time to direct his plane of regard horizontally forward. 



The character of the movements, the sudden onset in many cases (50), the 

 influence of accident, and the character of the tests used to bring out the 

 movements, all point to incoordination as the starting point of the disease. 



Preventive Measures. 



The results of this investigation show clearly that the most important 

 preventive measure is improvement in the lighting power of the miner's 

 lamp. If oil lamps are used, careful attention should be given to the clean- 

 ing of the lamps and quality of oil. If possible, a lamp giving a diffused light 

 should be introduced. Shades should always be fitted to the lamps to be 

 used in going to and from the face. (This is now in force in the Powell 

 Duffryn pits of the Ehymney Valley.) 



No man with error of refraction should be allowed to work underground. 

 Simple tests should be put to all fresh men by the managers, and if the 

 result is not satisfactory, the man should not be employed without a medical 

 examination. I believe that if this precaution were taken, half the cases of 

 nystagmus could be avoided. The introduction of coal-cutting machines in 

 thin seams is also of assistance. 



Table XXIV.— Use of Coal Cutters (43 Collieries). 





Collieries. 



Percentage of nystagmus. 



Extensively 



6 



0-49 



Partly 



15 



0-73 



Not used 



22 



0-81 



Improvement of ventilation, which also means a better light, is also of the 

 greatest importance, since the light given by a lamp falls off very rapidly as 

 the oxygen percentage of the air diminishes. 



I am now engaged in the measurement of illumination at the working 

 places, in experiments on the effects of introducing electric lamps, and in the 

 collection of further evidence as to the causation of the disease, with a view 

 to a further and much more full report. 



In presenting this preliminary report, I wish to acknowledge the very 

 great and willing help I have received from both the mining and the medical 



