GROWTH INDUCED BY DAMAGE
15
growth is limited to the damaged tissue. In other words, how specific is
the damage stimulus?
Damage to the epidermis, by stripping layers off the epidermis with
Scotch tape (Bullough and Laurence, 1960a; Lobitz et al., 1962; Pinkus,
1952), results in the stimulation of epidermal mitotic activity, but none
in the underlying dermis. Simple epidermal slit wounds made in the ears
of guinea pigs result in an increase in the number of epidermal cells
labeled with tritiated thymidine, but not labeled dermal cells (Hell and
Cruickshank, 1963). One might interpret these experiments to suggest
that the growth-promoting effects of damage are quite specific. However,
since the dermis does not normally show a proliferative response even
if it is damaged (Argyris, 1956a; Bullough and Laurence, 1960b; Gliicksmann, 1964), this kind of evidence cannot be used to indicate specificity
of the growth-promoting effects of damage. We may approach the question of specificity of damage-induced growth more profitably by asking
if damage to other tissues will stimulate the epidermis. Bullough and
Laurence (1960a), as we have indicated above, have shown that damage
to the panniculus carnosus, the subcutis, hair follicles, and dermis does
not result in an increased mitotic activity in the overlying epidermis.
Lobitz et al. (1962) have shown a similar degree of specificity in the
response of epidermis to damage, in human skin. Cutting into the skin
with a sharp knife, as parallel as possible to its surface, results in a
proliferative response by the hair follicles and sweat glands. The overlying uninjured epidermis, however, does not show an increase in mitotic
activity. It appears, therefore, that for the epidermis to be stimulated to
grow it must itself be damaged. Damage to other tissues of the skin is
not a sufficient stimulus for epidermal growth to occur.
We may next ask if the stimulation of hair growth is similarly tissuespecific, as it appears to be for epidermal growth. Damage to the connective tissue of the skin does not result in the stimulation of growth of the
resting hair follicles, since as we have already discussed, scraping the
underneath surface of a flap of skin does not stimulate hair growth, but
it does stimulate connective tissue growth (Argyris, 1964). But resting
hair follicles may be induced to grow if the epidermis is damaged,
although this is still controversial. T. S. Argyris and B. F. Argyris
(1962b) have shown that scraping the epidermis with a sharp razor leads
to epidermal proliferation and to the stimulation of growth of resting hair
follicles. Histological studies have been made in an attempt to rule out
the possibility that the resting hair follicles have been damaged in the
process of shaving. Chase (quoted in T. S. Argyris and B. F. Argyris,
15
growth is limited to the damaged tissue. In other words, how specific is
the damage stimulus?
Damage to the epidermis, by stripping layers off the epidermis with
Scotch tape (Bullough and Laurence, 1960a; Lobitz et al., 1962; Pinkus,
1952), results in the stimulation of epidermal mitotic activity, but none
in the underlying dermis. Simple epidermal slit wounds made in the ears
of guinea pigs result in an increase in the number of epidermal cells
labeled with tritiated thymidine, but not labeled dermal cells (Hell and
Cruickshank, 1963). One might interpret these experiments to suggest
that the growth-promoting effects of damage are quite specific. However,
since the dermis does not normally show a proliferative response even
if it is damaged (Argyris, 1956a; Bullough and Laurence, 1960b; Gliicksmann, 1964), this kind of evidence cannot be used to indicate specificity
of the growth-promoting effects of damage. We may approach the question of specificity of damage-induced growth more profitably by asking
if damage to other tissues will stimulate the epidermis. Bullough and
Laurence (1960a), as we have indicated above, have shown that damage
to the panniculus carnosus, the subcutis, hair follicles, and dermis does
not result in an increased mitotic activity in the overlying epidermis.
Lobitz et al. (1962) have shown a similar degree of specificity in the
response of epidermis to damage, in human skin. Cutting into the skin
with a sharp knife, as parallel as possible to its surface, results in a
proliferative response by the hair follicles and sweat glands. The overlying uninjured epidermis, however, does not show an increase in mitotic
activity. It appears, therefore, that for the epidermis to be stimulated to
grow it must itself be damaged. Damage to other tissues of the skin is
not a sufficient stimulus for epidermal growth to occur.
We may next ask if the stimulation of hair growth is similarly tissuespecific, as it appears to be for epidermal growth. Damage to the connective tissue of the skin does not result in the stimulation of growth of the
resting hair follicles, since as we have already discussed, scraping the
underneath surface of a flap of skin does not stimulate hair growth, but
it does stimulate connective tissue growth (Argyris, 1964). But resting
hair follicles may be induced to grow if the epidermis is damaged,
although this is still controversial. T. S. Argyris and B. F. Argyris
(1962b) have shown that scraping the epidermis with a sharp razor leads
to epidermal proliferation and to the stimulation of growth of resting hair
follicles. Histological studies have been made in an attempt to rule out
the possibility that the resting hair follicles have been damaged in the
process of shaving. Chase (quoted in T. S. Argyris and B. F. Argyris,