340 DR GEORGE WILSON ON THE 
2dly. A good deal of light must undergo irregular reflection and dispersion 
from the retina and choroid. But so much of this light as passes towards the 
front of the eye will be arrested in greater part by the abundant pigment of the 
ciliary processes, and anterior lateral portions of the choroid ; and what scatters 
laterally will only produce a general excitation of the retina without developing a 
second complete image of any visible object on the nervous membrane, which is 
the chief optical evil to be apprehended from intra-ocular reflection. So long 
as the direct seat of vision is not exposed to strong reflex illumination, and the 
same entire pencil of rays does not twice depict the image of the same object on 
different parts of the retina, and thus produce double vision of single things, the 
general reflection and dispersion of light within the eye cannot do more than di- 
minish the darkness of the eye-chamber as a whole. In the eye of the casual 
albino, light is liable to be returned from the back of the greatly contracted iris to 
the place of most perfect vision, and to disturb it, so that, as far as internal 
reflection is concerned, he would be better without an iris at all. Moreover, his 
iris is transparent, and is continually transmitting light from without as well as 
reflecting it from within. 
But even in the human albino, although unquestionably there must be painful 
dazzling of the eye from the continual action of light on every point of the retina, 
still, unless during sudden transitions from very faint to very bright illumination, 
involving great and rapid change in the area of the pupil, the yellow spot or place 
of perfect vision being opposite that aperture, will be less exposed than any por- 
tion of the retina to the impact of light which has undergone intra-ocular reflec- 
tion; and as the utmost contraction of the iris does not close the pupil, a pencil 
of rays reflected from the yellow spot, can never return 7m toto to repeat upon 
another portion of the retina the image which it has already produced upon that 
spot. 
It thus appears that the laws of luminous reflection do not necessitate imper- 
fect vision, as applied to the fact, that the retina and choroid return much of the 
light which reaches them, for :— 
lst, In the normal and also in the albino vision of all animals, man included, the 
amount of direct retinal and choroidal reflection is necessarily coincident with the 
width or degree of dilatation of the pupil; the larger the pencil of light entering 
the pupil, the larger the pencil leaving it, so that in every case the reflected rays 
are thrown out of the eye and do not disturb vision: further :— 
2nd, In those animals provided with tapeta lucida, such as the cat, the 
dog, or the ox, which are only partially nocturnal in their habits, the tapetum is 
so placed that in bright light it is not opposite to the contracted pupil, or is so only 
to a small degree.* When, however, the choroidal mirror is called into action in 
* Jouy Hunter, in Catal, of Museum of Royal College of Surgeons, London. Vol. iti., p. 165. 
