602 
SECOND REPORT- 1832. 
On a new Membrane in the Eye. By George H. Fielding, 
M.R.C.S. 
The object of this paper was to prove that immediately be¬ 
hind the retina and in connexion with it, there is a coloured 
membrane of a peculiar nature, distinct from the pigmentum 
nigrum. The eyes taken for the purpose of experiment were 
those of the ox and the sheep, in each of which the part in 
question, of a fine blue or green colour, appears at the back of 
the globe of the eye, immediately in contact with the retina, 
having behind it the true pigmentum. To prove the difference 
between this membrane and the pigmentum, the author quotes 
Dr. Young's account of the latter, in which it is described as 
composed of mucous and carbonaceous matter, as staining white 
paper, and easily removable from the choroi'des by washing it 
with water and a soft pencil ; but according to the author, the 
membrane in question will not stain white paper, nor will it part 
with its colour on the application of water. Its surface is bright 
and polished, and varies in colour according to the angle under 
which it is view r ed, and according as it is examined by reflected 
or transmitted light. A portion of it, w hich w 7 as of a pale blue 
by reflected light, appeared of a yellowish red by transmitted 
light; dipped in dilute sulphuric or muriatic acid, or in solution 
of ammonia, its colours begin to fade ; if it is then plunged into 
cold w 7 ater, they entirely disappear; if again into the acids or 
alkali, they reappear as bright as ever. The author infers that 
the colours depend not on any peculiar secreted matter, but on 
the general law 7 s for thin plates. 
Examined with a fine achromatic microscope of Chevalier s 
construction, blood-vessels, and even the red globules contained 
in them, were visible in the membrane. By careful dissection 
in water, it is separable in distinct layers from the choroid. Its 
colour is frequently different in the same species of animals ^ 
it is usually blue in the ox, the pigment in the same animal be¬ 
ing of a rich browm; in the cat and fox the membrane is of a 
golden yellow 7 , the pigment a rich black ; in the deer the mem¬ 
brane is pale blue, but the pigment a light brow n. 
The author proposes to name the subject of his researches 
Membrana versicolor ; he enters into some considerations con¬ 
cerning its probable use in the act of vision, suggested by its 
low reflecting pow r er and immediate connexion with the retina ; 
and supposes that vibrations are excited in it by the converg¬ 
ing pencils of light, and that these are communicated to the 
contiguous retina, and thus transferred to the brain. 
