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ALFRED J. COULOMBRE
brane. It is composed of lamellae disposed in the plane of the cornea and
separated by an interval of about 270 Â. In each lamella electron-dense
nodes are arranged in a regular hexagonal array with an internode
distance of 1,070 Â. Each node is connected to its immediate neighbors
by straight filaments approximately 100 Â in diameter. During development the coalescence of adjacent pads of this material is accomplished in such a manner that both the lamellae and matrices within the
lamellae join and register when the pads fuse. Furthermore, and apparently from the outset, the matrix of each lamella is in register with
those of adjacent lamellae. The chemical analysis of this membrane
identifies it as a form of collagen (Dohlman and Balazs, 1955).
Not only is the origin of Descemet's membrane associated with the
posterior epithelium, but that layer of cells also appears essential for the
regeneration of the membrane. After destruction of the posterior epithelium and Descemet's membrane, the constitution of an intact
posterior epithelium precedes the regeneration of Descemet's membrane
(Ranvier, 1898). Earlier Collins (1897) reported an instance of regeneration of Descemet's membrane associated with a regenerated posterior
epithelium. We yet await a definitive experimental demonstration of
whether or not the posterior epithelium synthesizes the substance of Beseemed s membrane.
VII. Transparency of the Cornea
After becoming progressively thicker and more opaque during the
early stages of development, the cornea reaches a point when it begins
to increase in transparency to the adult level (Fig. 2). This process is
gradual in the rabbit (Smelser and Ozanics, 1956, 1960) and abrupt in
the chick embryo (van den Hooff, 1951; Coulombre and Coulombre,
1958a). In the chick embryo the percentage of incident white light
transmitted by the cornea increases from 40% at 14 days of incubation
to the adult level (96%) at about 19 days of incubation. It is of some
interest to explore changes which are correlated with this remarkable
development and to summarize current thinking concerning its physical
basis.
During the period in which the cornea is increasing in transparency in
the chick embryo, it loses water rapidly and becomes thinner. It
achieves the adult level of hydration at the same time the adult level of
transparency is achieved (Coulombre and Coulombre, 1958a). The same
correlation between corneal dehydration and the increase in transparency is observed in the cornea of the developing rabbit (Smelser and
Ozanics, 1960). Coulombre and Coulombre (1958b) described two processes which could account for the dehydration of the cornea in the
chick embryo. One involves a progressive loss of water-binding capacity
ALFRED J. COULOMBRE
brane. It is composed of lamellae disposed in the plane of the cornea and
separated by an interval of about 270 Â. In each lamella electron-dense
nodes are arranged in a regular hexagonal array with an internode
distance of 1,070 Â. Each node is connected to its immediate neighbors
by straight filaments approximately 100 Â in diameter. During development the coalescence of adjacent pads of this material is accomplished in such a manner that both the lamellae and matrices within the
lamellae join and register when the pads fuse. Furthermore, and apparently from the outset, the matrix of each lamella is in register with
those of adjacent lamellae. The chemical analysis of this membrane
identifies it as a form of collagen (Dohlman and Balazs, 1955).
Not only is the origin of Descemet's membrane associated with the
posterior epithelium, but that layer of cells also appears essential for the
regeneration of the membrane. After destruction of the posterior epithelium and Descemet's membrane, the constitution of an intact
posterior epithelium precedes the regeneration of Descemet's membrane
(Ranvier, 1898). Earlier Collins (1897) reported an instance of regeneration of Descemet's membrane associated with a regenerated posterior
epithelium. We yet await a definitive experimental demonstration of
whether or not the posterior epithelium synthesizes the substance of Beseemed s membrane.
VII. Transparency of the Cornea
After becoming progressively thicker and more opaque during the
early stages of development, the cornea reaches a point when it begins
to increase in transparency to the adult level (Fig. 2). This process is
gradual in the rabbit (Smelser and Ozanics, 1956, 1960) and abrupt in
the chick embryo (van den Hooff, 1951; Coulombre and Coulombre,
1958a). In the chick embryo the percentage of incident white light
transmitted by the cornea increases from 40% at 14 days of incubation
to the adult level (96%) at about 19 days of incubation. It is of some
interest to explore changes which are correlated with this remarkable
development and to summarize current thinking concerning its physical
basis.
During the period in which the cornea is increasing in transparency in
the chick embryo, it loses water rapidly and becomes thinner. It
achieves the adult level of hydration at the same time the adult level of
transparency is achieved (Coulombre and Coulombre, 1958a). The same
correlation between corneal dehydration and the increase in transparency is observed in the cornea of the developing rabbit (Smelser and
Ozanics, 1960). Coulombre and Coulombre (1958b) described two processes which could account for the dehydration of the cornea in the
chick embryo. One involves a progressive loss of water-binding capacity