258 DR. HUBERT AIRY ON A DISTINCT FORM OF TRANSIENT HEMIOPSIA. 
cideclly brighter than the part seen against wall. At the junction between the two, I 
find great difficulty in recognizing the transition from lighter to darker. 
The eyesight thus affected, though wholly blind to boundaries of light and shade, is 
not disqualified for the reception of light, in quantity. The light is seen, almost unim- 
paired, though all definition is blurred and blotted out. 
But, besides being open to general impressions of light and shade from without, the 
clouded patch on the field of view has an inherent luminosity of its own. If the ob- 
server shuts his eyes and carefully shades them, or (better) retires into a dark room with 
his eyes open, he sees a faintly luminous curved figure in the dark, brilliantly edged 
along its serrated outline, — the bright margin supported by a trench of black, and in 
different places gleaming with red and blue and other colours. The tremor and boiling 
are beautifully seen (Plate XXV. figs. 1-9). 
Meanwhile the disease extends with gradually increasing rapidity, and spreading out- 
wards invades the more distant parts of the field of vision. Still the small end of the 
curve points ever to an imaginary cynosure at the centre of sight, the rest of the arch 
sweeping away into outer regions, where the mind has great difficulty in watching its 
form. Towards the outer extremity, where the zigzag pattern is much larger and less 
defined, and where the cloud dies away confusedly, as the disease attains its height, the 
turbulence of motion becomes greatly exalted ; the outskirts of the visual area seem to 
be boiling over with tumultuous light, that may be seen at times to collect itself in a 
rallying-point here and there, and presently to stream away again along the shore of the 
seething sea, splendid with large gleams of blue and red and green. 
The climax is generally reached in twenty or twenty-five minutes from the first 
beginning. Then the large arm, having overspread the margin of the field, begins to 
fade and leave the lower part to recover slowly from the storm. The small arm is the 
last to perish ; it remains in strength while the large arm is dying away ; but soon the 
outward spread carries it in turn to the upper margin of the field, and it there exhibits 
the same fervour that characterized the career of the larger end. The whole duration 
of the phenomenon is just half an hour, often with curious exactness. 
When the disease is about halfway advanced, I generally observe the rudiments of a 
fresh attack, beginning nearly where the first began, and sometimes advancing so far as 
to exhibit its bastioned margin, with rolling and tremor, as though the performance 
were to be rehearsed from beginning to end (Plate XXV. fig. 9, h). But there it stops 
and fades away, unless it arise on the opposite side, when I have known a second attack 
develope itself immediately after the first. 
The sight feels somewhat dazed for ten or fifteen minutes after the final disappearance 
of the phenomenon. 
Throughout the earlier part of this visual derangement I feel no discomfort at all ; 
my faculties are free to observe the phenomena closely and carefully. It is not till near 
the end, when the boiling is at its height, that the eyes feel oppressed, and the head 
has a presage that it is going to ache. The headache comes on gradually : it is not 
