THE PIGMENT CELLS OP THE BETINA.
365
The Figment Cells of the Retina.
By
J. 8. Boden and F. C. Sprawson,
Students of Medicine, King's College, London.
IN preparing a specimen of the retinal pigment cells from a
sheep's eye in the practical histology class at King's College
one of us (S.) noticed that these were not all hexagonal in
shape, as is usually described, but that many had seven sides;
and on searching through the specimen, cells with varying
numbers of sides were found. On showing this to Professor
Halliburton he suggested that we should examine a large
number of specimens from different animals, in order to ascertain if the same irregularities exist there. This we have done,
and the present paper contains the results of the investigation.
The descriptions and figures in the various text-books are
taken from Max Schultze's work on the subject.1 In all, the
cells are represented as being perfect hexagons, and the existence of cells of other shapes is not mentioned.
The method of preparation we employed was as follows:—
The eye was removed from the body, and an incision having
heen made through the sclerotic, it was placed in Miiller's
fluid for a few days. It was then transferred to very dilute
Miiller's fluid for a day or two in order to macerate it a little,
and the eyeball freely opened ; the black pigment layer can be
stripped off fairly easily. Portions of this were mounted in
glycerine or Farrant's solution, and examined unstained. In
some cases, especially when we examined that portion of the
1
' Archiv f. mikr. Anat.,' vol. ii, and Strieker's ' Handbook of Histology.'
366
J. S. BODBN AND P. 0. SPBAWSON.
epithelium which in the region of the tapetum lucidum contains no pigment, the specimens were first stained with dilute
magenta before being mounted.
The specimens were taken from the eyes of the sheep, ox,
rabbit, kitten, pig, frog, and hen. In all cases the results
were the same. Hexagonal cells are certainly the most
numerous; heptagonal cells come next, and scattered at intervals throughout a preparation, cells with four, five, eight, nine,
ten, and eleven sides are also found. In all cases there is
never anything of the nature of a gap ; the mosaic appears to
be always perfect. This is true for all parts of the epithelium
—that is to say, in the cells richly laden with pigment in the
tapetum nigrum, and also in the unpigmented cells over the
tapetum lucidum when that is present.
We included the hen in the list of animals the eyes of which
we examined, as it was from the retinal epithelium of this
animal that Max Schultze's figures were drawn. Here the
shape of the cells is certainly much more uniform than in
mammalian eyes, but we saw amidst the hexagonal cells several
with five, seven, eight, and nine sides.
There can be no doubt that the polygonal shape of the cells
is due to mutual pressure, and if all the cells were of the same
size they would be necessarily hexagonal. In the process of
growth, however, some cells, receiving presumably more nutriment, grow to a greater size than their fellows. The result of
this is that the bigger cells come into relation with a larger
number of ordinary sized cells, and so become more than sixsided ; and in a similar manner the smaller cells are less than
six-sided. This view is fully borne out by a number of
measurements we have made. The number of sides in a cell
varies directly as its size.
We give below the measurements we have made in the case
of the sheep and ox. The measurements were made with the
aid of a camera lucida, and the numbers below give the longest
and shortest diameter of the cells.
THE PIGMENT CELLS OF THE RETINA.
lmber
aides.
4
4
5
6
6
7
8
8
9
9
10
Figment layer from
eye of Suecp.
16/i x 13/.
15/i
19/i
28/i
20/i
20/i
28-5/1
X 15/i
X 16/i
X 15/i
x 19-5/1
X 165/1
X 19/i
34-5/. x 22/i
24/i x 21/i
367
Pigment layer froc
eye of Ox.
14/i x 12/i.
ll/i x 8-5/i.
13/i x 12/t.
17/i X 16/i.
32/i x 17/i.
32/t x 22/t.
34-5/1 x 21/i.
32/i x 24-5/i
38/i X 27/i
42u x 25u.
Among the mammals examined we noticed that the pigment
cells from the rabbit's eye were exceptionally large, the hexagonal cells measuring as much as the eight- to ten-sided cells
from the retina of the ox and sheep.
In our examination of the retinal epithelium our chief
resu.lt has thus been that the term hexagonal as applied to it
is not correct; polygonal would be better. Among minor
points we have also observed that many of the larger cells—
namely, those with eight, nine, and ten sides—have two nuclei.
With regard to the shape of the pigment particles in the cells,
most of them appear to be fusiform or rod-shaped, as described
by Max Schultze. Many, however, are spherical or approximately so, and certain others are spherical with a rod-like
projection from one side of the sphere, as though the spherical
granule were elongating to form a rod.
NOTE.—Since the above was written we have had an opportunity of examining the retinal pigment cells from a human
foetus (aged about seven months). The cells there presented
the same general characters as described above, but the proportion of non-hexagonal cells was smaller than in the eyes
of the other mammals we have examined.
We have also found, in Jabez Hogg's book on the ' Microscope/ a figure of the retinal pigment cells which indicates
their polygonal rather than hexagonal shape, but in the
descriptive letterpress no allusion is made to this fact.