Barrett—On Entoptic Vision. 129 
In making the experiment, the candle should be held at the 
side of the head, a little helow the level of the pupil, and the gaze 
directed away from the candle. If now the lighted candle be 
slowly waved to and fro, either laterally or vertically, whilst the 
glare of the candle is seen on the one side, the shadows of the 
vessels will be seen projected on the other side towards which the 
gaze is directed. 
After the eye has been in complete darkness for some time, a 
curious entoptic phenomenon can be seen when a lighted candle 
is held near the eye. Numerous streams and patches, of what 
seems to be a light flocculent matter, will be seen quickly moving 
on a dark purple background, which covers the field of vision. 
The appearance somewhat resembles a very brisk agitation and 
settling of curds in a purple whey. In the course of half a 
minute or less the moving flocculent streams clear off, and the 
retina assumes its normal state. The experiment is best made 
after waking up in the night, and immediately after lighting a 
bedside candle. It is possible that this phenomenon, which does 
not appear to be mentioned by any writer on physiological optics, 
may be connected with the presence of the visual purple on the 
retina. 
5. Movine Corpuscies. 
There remains to be described another Entoptic phenomenon 
to which a brief reference was made in Part III. of these papers.’ 
I refer to the rapid succession of bright specks like minute fire- 
flies which are seen darting across the field of vision when a 
bright sunlit sky is viewed through a cobalt-blue glass. This 
phenomenon was first noticed by the eminent physiologist Vierordt, 
in 1856,? who observed it when looking at a bright sky through 
the fingers of his hand, which were waved rapidly to and fro in 
front of the eye; and he connected the appearance with the 
circulation of the blood in the capillaries of the retina. Inter- 
mittent light does not, however, reveal the appearance so well as a 
blue glass, or a solution of ammonia-sulphate of copper. 
1 Proc. Roy. Dublin Soe., vol. xi., p. 85. 
* Archiv fiir physiol. Heilkunde, 1856, Heft 11. 
