of Edinburgh, Session 1881-82. 
597 
During my recovery, I frequently experimented upon tlie optical 
vertigo. These experiments were suggested by an accidental 
observation. Having put out the drawing-room gas one evening, as 
I was leaving the room I saw the reflection of outside gas lamps in 
the glass of a picture hanging on the drawing-room wall, and these 
lights seemed to me to be moving exactly as if the picture were 
swaying on its cord. I then turned and stood before the picture. 
I satisfied myself that the picture was motionless. I then made 
about half a rotation, that is, I turned slowly till my back was to 
the picture, and quickly turned and faced it. I then saw the lights 
move to the right or left as the case might be, the sense of the 
apparent rotation of the lights being the opposite of my real rotation. 
This experiment I frequently made to find how I was getting on, 
but found that I could not repeat it on real lights seen directly 
through the window. 
Quite lately I tried whether I could produce any trace of the 
feelings which were so familiar to me then. By rapidly spinning 
round three or four times, I find that I can produce very much the 
same sensation which half a turn produced when I was just well 
enough to walk. The sensation now lasts two or three seconds, 
then it lasted sometimes one, sometimes more than two minutes. 
It is worth noting that during the whole course of the illness there 
was never any disturbance or irregularity in the sense of hearing. 
So far for the facts of the case. The points of interest seem to 
me to be : — (1) That the vertigo never occurred unless provoked by 
a real rotation of the head. (2) That the phenomena were perfectly 
symmetrical. (3) That the axis of the apparent rotation was always 
the same as that of the real rotation which had provoked it, while 
its sense was the opposite. The vertigo was in fact only a very 
much exaggerated form of a perfectly natural phenomenon. It 
might, therefore, be supposed that the morbid condition was a 
sort of hypersesthesia of the sense of rotation. This, however, was 
not the case. The direct sensitiveness to ordinary rotations was if 
anything diminished, it was the after effects of rotations that were 
greatly increased both in intensity and in duration. (4) Visual 
vertigo often ceased when there was sufficient evidence that 
external bodies were really at rest. Thus, as soon as the illuminated 
rectangle was recognised as the window, the displacement of the 
vertical ceased, and the window was seen in its real position. 
