332 DR GEORGE WILSON ON THE 
readily examined, and I see no reason to doubt that photographic images of 
the retina and choroid may be obtained and preserved on collodionised or other 
actino-sensitive surfaces. 
By means of such Ophthalmoscopes, in the hands of Heimuo.rz, Coccrus, 
Ruete, and others, it has been placed beyond question, that much of the light 
which enters the human eye is reflected from the anterior surface, or from some 
depth within the layers, of the retina, without entirely traversing that membrane, 
or reaching the choroid, so as to be subjected to the absorptive action of its dark 
pigment. So far, therefore, as the accepted theory of vision demands that the 
light which has reached the retina shall not return across the chamber of the 
eye, it must be abandoned; and the evils which are supposed to be inseparable 
from such cross lights, or luminous reverberations, are encountered at every mo- 
ment by every eye, whether animal or human, at least in the case of the Verte- 
brata, which is engaged in the exercise of vision; yet it is vision so marred and 
obstructed which we are in the habit of calling perfect. We must plainly mend 
our theory, or our language, for they are inconsistent with each other. 
Before seeking to determine which must be altered, it is important to notice, 
that, according to the views of certain recent writers on the eye, among whom I may 
specially name KoLuiker and Henry Mier, the German physiologists, it is not 
the anterior part or face of the retina, but its deeper portions which are optically 
sensific ; and light must penetrate to them before the sensation of vision can be ex- 
perienced. If this view be well founded, then we may be led to the somewhat start- 
ling conclusion, that much of the light which is reflected from the retina, at the best 
contributes nothing to vision whilst within the eye, even if we deny that it posi- 
tively obstructs it. And if we suppose, with the older authorities, that all the light 
which reaches the retina penetrates it sufficiently deeply to excite luminous sen- 
sation, then it is manifest that so far as that portion which is reflected outwards 
is concerned, the dark surface of the choroid is quite superfluous.* 
* J am indebted to my pupil, Mr James Warprop, an accomplished theologian and naturalist, 
for an abstract of the views of Kétniker and H. Mijtuer, Their opinions are contained in KGLLIKER’s 
Micr. Anatomie, B. 2, Zweite Halfte 606-720. See also H. Miitter’s Remarks on the Structure 
and Funetion of the Retina, translated in the Quarterly Journal of Micr. Science, July 1853, pp. 
269-273. Without entering into the minute discussion of anatomical questions which I am not 
competent to decide, it may be noticed, that both the skilful observers referred to, agree in denying 
to the fibres or expansion of the optic nerve, the function of perceiving “objective light.” This fune- 
tion belongs, according to them, to the deepest of the five layers of which they regard the retina of 
vertebrate animals as composed. This layer, which is immediately in front of the choroid, is thus 
described by K6r11Ker :-—“ The external or bacillar layer consists of the ‘ rods and bulbs’ (bacilli 
et coni), whose ends evenly terminated, form a sort of mosaic pavement towards the black pigment, 
and which internally are continued by fibres (Miitzer’s fibres) through the three succeeding retinal 
layers, to abut abruptly, and with radiating terminations on the external aspect of the fifth layer, 
which, however, they do not penetrate.” This fifth layer is a very delicate membrane, investing the 
entire internal or anterior aspect of the retina. 
Accepting this description as well-founded (and it has received the approbation of the majority of 
recent physiologists), it appears that light must more or less traverse the anterior layers of the retina, 
till it reaches the “ rods and bulbs,” with their connecting radiating fibres, before it can excite a 
