1911.] The Causes and Prevention of Miners' Nystagmus. 15 



quotes figures which show that with improvement of the lamps used there is 

 a great diminution in the percentage of nystagmus. After the introduction 

 of the powerful Wolf lamp in 1908 the cases of nystagmus at one pit fell 

 50 per cent, below the figures of the same pit in 1891. 

 He quotes Lewillon of Mons ((1) p. 84) — 



Percentage of cases with the Mueseler lamp 38 



„ „ electric lamp 19 



Court (6) gives the following figures as result of a systematic examina- 

 tion — 



597 men from a safety-light pit 207 cases of nystagmus. 



572 „ naked .„ 32 „ „ 



Of these 32 cases, 29 had worked in a safety-light pit at one time. 

 Libert (7) :— 



825 hewers with Narsaut or Mueseler lamp 35"3 per cent. 



316 „ benzine lamp 24 - 4 „ 



Stassen (3), on the other hand, says that the number of cases is almost as 

 great in a naked-light pit as in a safety-light pit. 



The alternative theory is that position has the predominating influence. 



Snell(17), in particular, says that holing* is responsible for almost all cases. 

 He says that the direction of regard is upwards, and that a great strain is 

 thrown on the elevator muscles of the eye. In my experience, a man when 

 he holes looks directly forward, striking the coal at the level of his eyes. 



Eeid (19) and Jeaffreson (18) say that the condition is due to a disassocia- 

 tion of the movements of the head and eyes and the strain of working in a 

 bad light. Eutten (21), who expresses the current German idea, says that 

 it is due to a compensatory movement of the eyes set up to oppose any 

 inclination of the head or body from the normal (" Gegenrollung "). 

 Peters (22) suggests that the affection is due to affection of the inner ear 

 (labyrinth) ; Elworthy (23), that it is due to absence of colour and 

 corresponding retinal fatigue. 



Conditions Determining the Occurrence of Miners' Nystagmus. 

 My chief aim, up to the present, has been to obtain statistical and other 

 evidence as to the conditions which obtain in work, with a view to pointing 

 out the way to prevention ; and the 400 cases investigated have been analysed 

 with this end in view. 



* A method which the collier sometimes uses to win his coal. The coal is undercut a 

 distance of 3 or more feet and then wedged down from the top. The miner in many 

 cases has to lie on his side, and often drags his body under the ledge he has cut. 



