242 REPORTS ON THE STATE OF SCIENCE.—1914. 
or its modifications, so that it is rare, even in coal-mines, to find 
cases of nystagmus where more powerful illuminants such as candles 
and electric lamps are used. Moreover, the great absorption of light by 
the coal-surface diminishes the illuminating value of the lamp employed. 
This absence of reflections from walls, floor, and ceilings interferes 
with clear visualisation, since direct rays are never so satisfactory as 
diffuse rays. The other factor mentioned above—muscular strain, 
especially of the elevators of the eyeballs—is also taken into considera- 
tion, notwithstanding the difference of opinion on the importance of 
this. Snell has collected several cases of nystagmus which, as in the 
case of compositors, has followed strain in this way, and we have 
ourselves found that there is a larger number of cases of miners’ 
nystagmus associated with ‘holing’ than in any other occupa- 
tion underground—under conditions, therefore, which demand an 
awkward posture with straining of the head and eyes. Other sources 
of peripheral irritation are opacities of the media, errors of refraction, 
pigmentary and other ocular defects, which tend to produce or aggravate 
nystagmus by either modifying illumination or by causing muscular 
strain or by interfering with the direct rays on the fovea. 
Taking all these factors, however, into consideration—factors which 
are generally acknowledged—the fact remains that, working under 
similar conditions of illumination and strain, a large percentage of 
miners do not develop nystagmus, and it is our object to find out what 
is the decisive factor. Admitting the external factors in those who 
develop nystagmus to be more or less constant, admitting the occa- 
sional possibility of peripheral factors such as those above mentioned, 
there remains some factor unaccounted for which explains the selection 
of certain miners for this trouble. At this stage of our inquiry, how- 
ever, we investigated what seemed to us a neglected field—the relative 
sensibility of the retina in the foveal and in the perifoveal regions— 
and for this reason. The peculiar modifications which the dark-adapted 
eye undergoes might bring about a still further interference with the 
illumination by a reactive function on the part of the percipient. 
A consideration of the conditions of work in the coal-mine sug- 
gested very strongly the importance of the possession by the miners 
of delicate vision sensibility. Before dark-adaptation could be fully 
developed the miner at his first entry into the pit would have to 
strain his vision under the most trying circumstances to avoid roof 
obstacles as he made his way to his work. Such a strain would display 
itself in the muscles chiefly involved, such as the elevators of the 
eyelids and of the eyes. It is interesting clinically to find the initial 
symptom complained of is a heaviness of the lids. 
At work on the coal-face the miner with his eyes on the coal- 
surface would be subjected only to a few reflected rays from smooth 
facets of coal and some little diffused light from the coal-surface 
generally. Very dim light would bring out the latent differences in 
the visual sense, such as the differences of acuity between foveal and 
perifoveal vision. If the rays were too feeble to excite foveal sensation 
they might yet stimulate perifoveal sensation. ; 
Our theory regarding this particular feature of the eye was that a 
