260 DR. HUBERT AIRY OH A DISTINCT FORM OF TRANSIENT HEMIOPSIA. 
I have been attacked when I have been called early after insufficient sleep. Some- 
times the attack has been nocturnal, mingling with a dream, from which I wake and 
find the spectacle in full fervour. Sometimes, I believe, I have passed through it with- 
out waking, for I have been half aware of it m my sleep, and have found the dull head- 
ache on me in the morning. 
Not unfrequently I have found it impossible to assign any cause for the attack. 
Position in the field . — The first spot of blindness never springs up (with me) exactly 
in the centre of vision. Even when most central, it is recognized as lying a very little 
to one side or the other; and this slight excentricity determines the side of the field 
which the disease will occupy in its development. With me, the left side is affected 
more frequently than the right. The most usual position of origin is 3° or 4° to the 
left of, and 3° or 4° below, the centre. I remember one case in which the attack began 
at a much greater distance in the same direction ; but I have never had any experience 
of such a course of the cloud as Sir J. Herschel describes in his paper quoted above 
(p. 251), coming into view at the extreme left, and gradually extending to the right over 
the whole field. 
Anomalies in the course of the Disease . — In one or two cases, after reaching a certain 
point of development, the phenomenon has died away without ripening ; it has suffered 
breach of continuity in its walls opposite the natural gap, and then each part has faded 
separately (Plate XXVI. fig. 3). In one of these cases the disease began at the beginning 
of a walk before breakfast in summer, and died prematurely as I walked briskly on. In 
the case above alluded to as having taken origin at an unusual distance below and to 
the left of the sight-point, the cloud preserved its contour unbroken for an unusual 
length of time, and took a marked oval shape, until the gradual approach of its wall 
towards the centre led to an opening on that side, with adhesion of one arm (small-toothed) 
to the centre, and retreat of the other (large-toothed) towards the periphery of the field. 
In only one instance have I noticed the small end of the curve refusing allegiance to the 
centre of sight, and then the course of the phenomenon corresponded to that given in 
the diagram that accompanies Professor Airy’s paper on Plemiopsy. 
I believe the small end of the curve is always the upper of the two. It is so in all 
the cases of which I have kept any record, and I cannot remember any instance of the 
reverse *. 
The shape of the curve has varied considerably in different instances. Sometimes it 
has been as flat as is represented in Professor Airy’s diagram, when the phenomenon 
has not been well developed in other respects ; but in far the greater number of cases it 
assumes a full horseshoe shape. 
When a second attack has followed close upon the first, I have noticed that, besides 
the flattening of the curve, the salient angles of the margin have been less defined, and 
the marginal lines of light less clear. 
* Since writing these words (1870, Jan. 23) I have had an attack of destral teichopsia, in which the lower 
arm had the smaller pattern, and offered rather distant allegiance to the sight-point. 
