GROWTH
INDUCED BY
DAMAGE
3
1960). Epidermal proliferation is not first seen in the cells immediately
bordering the wound, but in those about a millimeter from the wound
edge (Arey, 1936; Bullough and Laurence, 1960a). It is not until a few
days later that the cells abutting the wound edge begin to show an
increase in mitotic activity. Why the epidermal cells bordering the wound
do not immediately proliferate is not known. It has been suggested that
they are sublethally damaged so that they cannot respond (Arey, 1936).
This speculation is supported by the experiments of Pinkus (1952) who
has shown that mild damage of the epidermal surface of human skin,
produced by stripping off the most superficial layers, using Scotch tape,
results in a quick and intense mitotic stimulation of the basal cell layer.
But, if the stripping is repeated so that more of the superficial epidermal
cell layers are removed, the basal cells do not show as quick and as
intense a mitotic stimulation. This problem deserves further investigation
since an explanation why different degrees of damage will either inhibit
or stimulate cell division is important.
It is generally believed that the mitotic proliferation of the epidermis,
when fully activated, is limited to about 1 mm from the wound edge
(Arey, 1936; Bullough and Laurence, 1960a; Gillman and Penn, 1956).
Recently, however, reports have appeared that demonstrate an increased
uptake of tritiated thymidine into epidermal nuclei beyond 1 mm from
the wound edge (Block et al, 1963; Hell and Cruickshank, 1963). Therefore this question should be reopened and investigated with the newer
techniques available.
In addition to stimulating cell proliferation, damage also activates the
movement of epidermal cells to close the wound gap. The detailed kinetics
and mechanics of this cell movement still remain to be worked out, even
though much work has been done (Abercrombie, 1964; Arey, 1936;
Johnson and McMinn, 1960; Lash, 1955). Most investigators believe that
the migrating cells do not undergo mitotic activity (Arey, 1936), although
recently claims have been made that the moving cells may show mitotic
activity (Johnson and McMinn, 1960).
Whether or not a common stimulus initiates cell movement and cell
proliferation of the epiderimal cells has not been resolved. Weiss and
Matoltsy (1959) have shown that, in the chick embryo, skin wounds
initiate only cell proliferation if the wound is made before the twelfth
day of incubation. Wounds made later result in cell proliferation and cell
movement. These results can be interpreted as evidence that different
stimuli initiate cell proliferation and cell movement. However, they may
be also interpreted to demonstrate that the ability for cell movement
INDUCED BY
DAMAGE
3
1960). Epidermal proliferation is not first seen in the cells immediately
bordering the wound, but in those about a millimeter from the wound
edge (Arey, 1936; Bullough and Laurence, 1960a). It is not until a few
days later that the cells abutting the wound edge begin to show an
increase in mitotic activity. Why the epidermal cells bordering the wound
do not immediately proliferate is not known. It has been suggested that
they are sublethally damaged so that they cannot respond (Arey, 1936).
This speculation is supported by the experiments of Pinkus (1952) who
has shown that mild damage of the epidermal surface of human skin,
produced by stripping off the most superficial layers, using Scotch tape,
results in a quick and intense mitotic stimulation of the basal cell layer.
But, if the stripping is repeated so that more of the superficial epidermal
cell layers are removed, the basal cells do not show as quick and as
intense a mitotic stimulation. This problem deserves further investigation
since an explanation why different degrees of damage will either inhibit
or stimulate cell division is important.
It is generally believed that the mitotic proliferation of the epidermis,
when fully activated, is limited to about 1 mm from the wound edge
(Arey, 1936; Bullough and Laurence, 1960a; Gillman and Penn, 1956).
Recently, however, reports have appeared that demonstrate an increased
uptake of tritiated thymidine into epidermal nuclei beyond 1 mm from
the wound edge (Block et al, 1963; Hell and Cruickshank, 1963). Therefore this question should be reopened and investigated with the newer
techniques available.
In addition to stimulating cell proliferation, damage also activates the
movement of epidermal cells to close the wound gap. The detailed kinetics
and mechanics of this cell movement still remain to be worked out, even
though much work has been done (Abercrombie, 1964; Arey, 1936;
Johnson and McMinn, 1960; Lash, 1955). Most investigators believe that
the migrating cells do not undergo mitotic activity (Arey, 1936), although
recently claims have been made that the moving cells may show mitotic
activity (Johnson and McMinn, 1960).
Whether or not a common stimulus initiates cell movement and cell
proliferation of the epiderimal cells has not been resolved. Weiss and
Matoltsy (1959) have shown that, in the chick embryo, skin wounds
initiate only cell proliferation if the wound is made before the twelfth
day of incubation. Wounds made later result in cell proliferation and cell
movement. These results can be interpreted as evidence that different
stimuli initiate cell proliferation and cell movement. However, they may
be also interpreted to demonstrate that the ability for cell movement