210
CHARLES S. THORNTON
particularly rich in the promoter factor. X-irradiation of blastemal
homogenates destroyed the promoter effect (Semkowicz, 1964).
Recuperation
of regenerative ability in the postmetamorphic frog has
also been attributed to the activation of wound substances. Polejaieff
(1936) found that hind limb regeneration in tadpoles in metamorphic
climax could be re-evoked after extensive pricking of the amputation
surface with a needle. Rose (1944) excessively traumatized the amputation surface of postmetamorphic frogs by NaCl treatments which induced
processes of regeneration. Subsequent work (Gidge and Rose, 1944)
indicated that salt treatment had an important effect on wound healing.
Wound healing in the amputated limb of the adult frog is accomplished
by the movement of whole skin (dermis and epidermis) over the wound
surface. In tadpoles capable of regeneration, wound healing is accomplished by movement of epidermal layers alone. When larval skin
replaced normal adult skin on the frog limb stump, regeneration became
possible. Other investigators have implicated wound epithelium as an
important factor in initiating regeneration. For example, head skin
inhibits regeneration when it replaces normal limb skin in
Ambystoma
talpoideum larvae. In these cases wound healing by epidermal migration
occurs but a typical "wound epithelium," composed of undifferentiated
epidermal cells, is not formed and blastemal cells fail to aggregate to
form a regeneration bud (Thornton, 1962).
The induction of supernumerary
limbs by means of foreign implants
into the host limb exhibits many of the features of the initiation of
typical limb regeneration, particularly since both phenomena are invariably associated with tissue trauma. Indeed the importance of trauma
in accessory limb induction has led Ruben (1960) to propose that the
foreign implant (i.e. frog kidney) stimulates the activity of the host
rejection system which then brings about the traumatization of the
implant. The histolyzing implant in its turn causes local histolysis of
the host tissues thus "causing the establishment of a new partial limb
field" (Ruben and Stevens, 1963, p. 279). In support of this model Ruben
has observed that genetic disparity between host and donor seemed to
be very important in the induction of accessory limbs and that a basic
requirement of stimulation is the initiation of histolysis, and often
cytolysis, in the host tissues. Carlson and Morgan (1967) find that
boiling at 100°C for 10 minutes destroys the ability of frog kidney to
induce supernumerary limbs in the newt, but that lyophilization does not.
This agrees with results of Stevens et al. (1965) who found increased
CHARLES S. THORNTON
particularly rich in the promoter factor. X-irradiation of blastemal
homogenates destroyed the promoter effect (Semkowicz, 1964).
Recuperation
of regenerative ability in the postmetamorphic frog has
also been attributed to the activation of wound substances. Polejaieff
(1936) found that hind limb regeneration in tadpoles in metamorphic
climax could be re-evoked after extensive pricking of the amputation
surface with a needle. Rose (1944) excessively traumatized the amputation surface of postmetamorphic frogs by NaCl treatments which induced
processes of regeneration. Subsequent work (Gidge and Rose, 1944)
indicated that salt treatment had an important effect on wound healing.
Wound healing in the amputated limb of the adult frog is accomplished
by the movement of whole skin (dermis and epidermis) over the wound
surface. In tadpoles capable of regeneration, wound healing is accomplished by movement of epidermal layers alone. When larval skin
replaced normal adult skin on the frog limb stump, regeneration became
possible. Other investigators have implicated wound epithelium as an
important factor in initiating regeneration. For example, head skin
inhibits regeneration when it replaces normal limb skin in
Ambystoma
talpoideum larvae. In these cases wound healing by epidermal migration
occurs but a typical "wound epithelium," composed of undifferentiated
epidermal cells, is not formed and blastemal cells fail to aggregate to
form a regeneration bud (Thornton, 1962).
The induction of supernumerary
limbs by means of foreign implants
into the host limb exhibits many of the features of the initiation of
typical limb regeneration, particularly since both phenomena are invariably associated with tissue trauma. Indeed the importance of trauma
in accessory limb induction has led Ruben (1960) to propose that the
foreign implant (i.e. frog kidney) stimulates the activity of the host
rejection system which then brings about the traumatization of the
implant. The histolyzing implant in its turn causes local histolysis of
the host tissues thus "causing the establishment of a new partial limb
field" (Ruben and Stevens, 1963, p. 279). In support of this model Ruben
has observed that genetic disparity between host and donor seemed to
be very important in the induction of accessory limbs and that a basic
requirement of stimulation is the initiation of histolysis, and often
cytolysis, in the host tissues. Carlson and Morgan (1967) find that
boiling at 100°C for 10 minutes destroys the ability of frog kidney to
induce supernumerary limbs in the newt, but that lyophilization does not.
This agrees with results of Stevens et al. (1965) who found increased