132 Scientific Proceedings, Royal Dublin Society. 
against this hypothesis. ‘The dimension of the specks corresponds 
very well with that of the white corpuscles, the average diameter 
of which is about 555 of an inch, whereas the red corpuscles 
in man are 3555 of an inch, or 0°007 mm. in diameter. ‘The 
white corpuscles are much fewer in number than the red: the 
proportion varies, being about 1 to 1000 red after fasting, but 
after a meal they rise to about 1 to 400 red ; they are distinguished 
also by their solitariness, their higher refractive power, their 
spherical shape, and their transparency. They also exhibit 
amceboid movements, and the protoplasm of which they consist 
“presents a network of very fine contractile fibrils ”’ (Carpenter). 
The function of the blue glass in enabling the phenomenon to 
be perceived now becomes apparent. Viewed through such a 
glass the red corpuscles either would not be seen at all or would 
appear as faint dark specks, whereas the transparency of the 
white corpuscles would cause them to be seen as bright specks. A 
simple experiment illustrates this. Scattering on a black surface a 
number of small fragments of bright-red paper, interspersed with 
some minute scraps of white paper, the latter are hardly discern- 
ble amid the red until a blue glass is interposed; now the white 
particles are vividly seen, whilst the red disappear, and are indis- 
tinguishable from the black surface. Hence the more perfectly 
monochromatic the blue medium—e.¢., a solution of the ammonia- 
sulphate of copper,—the more conspicuous will become the moving 
corpuscles in the eye, as I found to be the case. 
I am therefore of opinion that the appearance is due to the 
white blood-corpuscles, either in the retinal vessels or migrating 
from the capillaries. The rapidly moving points of light which 
are seen may be due to those corpuscles which are near the walls 
of the capillary vessels acting as minute spherical lenses; and the 
larger specks, with a slower and more wandering movement, may 
be the amceboid movements of the white corpuscles which have 
escaped through the walls of the vessels. 
But these questions must be left to the consideration of 
physiologists, who will, I hope, be led to repeat these and other 
experiments on Entoptic vision, more especially in view of the 
great importance attached to the white corpuscles, or phagocytes, 
since Metchnikoff propounded his doctrine of phagocytosis. It 
becomes, therefore, of the utmost interest to watch the behaviour 
