334 DE GEORGE WILSON ON THE 



Coccius specially refer to the varying colours of the " background" as they term 

 it, of the eye, i. e., the retina and choroid taken together, which is never black, 

 nor even brown, but bright red when the pigmentum nigrum is scanty, yellowish- 

 red when it is more abundant, and brownish-red when it is largely present. 

 Coloured drawings are given in illustration of these statements.* 



Messrs Bader and Roberts describe the choroid as exhibiting under the oph- 

 thalmoscope, " a brilliant red surface," and state more particularly, that this 

 membrane is " covered by a very tender, pointed, grayish-brown layer of pigment, 

 giving the appearance of an uniform red surface ;" adding that " a comparison of 

 many healthy eyes of different ages is needed for the purpose of having a correct 

 idea of the normal red of the choroid." f 



In the comparatively few observations which I have been able to make on the 

 appearance of the choroid through Helmholtz's speculum, it has appeared yellow- 

 ish-red, and it is thus represented in Ruete's drawings. Some allowance must 

 doubtless be made for the quality of the light employed, which is always from an 

 artificial source when ophthalmoscopes are used ; but after allowing for this, it ap- 

 pears that even minute medical observers are content to describe the choroid as 

 uniformly red or yellowish-red, and that in the darkest human eyes it deepens only 

 by a degree or two into brownish-red. In short, whereas, were the choroid so 

 powerfully absorbent of light as it is generally supposed to be, it should more or 

 less resemble, as seen through the retina, polished ebony or walnut wood, it re- 

 flects so much red light, that one who saw it for the first time, would probably 

 at once credit the statement, that he was gazing on the choroid, not of a normal, 

 but of an Albino eye. 



The choroid thus, as well as the retina, is a reflector of light, and deprives 

 the eye of the character of a camera obscura ; nor can it have escaped the notice 

 of the able Germans to whom we are indebted for the first full exposition of this 

 truth, that it necessitates an alteration in the current theory of vision. Yet so 

 far as I am aware, no alteration of that theory has hitherto been proposed by any 

 writer ; nor are the facts which demand a change as yet familiar to opticians or 

 natural philosophers who are not physiologists. \ 



The reluctance which has thus been shown to include in an altered theory of 

 vision the occurrence of deep reflection of light within the eye, appears to be 

 based upon three considerations. The 1st, that in the eyes of human Albi- 



* Bildliche Darstellung, Tab. II. f Brit, and For. Medico-Chir. Rev., April 1855, p. 509. 



J Since reading this paper to the Society, I have learned from Mr Wardrop's Abstract of Kolli- 

 ker's paper, that some of the latter's countrymen suppose that the bacillar layer of the retina reflects 

 light on the optic fibres, and thus enhances vision. Kolliker's words are " This bacillar layer does 

 not act as a catoptrical apparatus, as Hannover, Bru'cke, and Helmholtz think, for reflecting the 

 light back to the optic fibres, but as a true nervous apparatus for itself receiving the impression."- 

 (Micr. Anat., B. ii., Zweite Halfte, p. 691.) Even, however, were the view objected to by Kolliker 

 well-founded, it would not dispose of the question discussed in this paper, for the main direction of 

 the light reflected from the bacillar layer of the retina must be forwards and ontwards, so as to illu- 

 minate more or less the entire chamber of the eye. 



