AMPHIBIAN LIMB REGENERATION
211
supernumerary limb induction by previously frozen newt kidney, compared to fresh newt kidney, but this inducing effect was destroyed by
boiling. Thus a protein would seem to be indicated. Also pertinent here
are the results of Malinin and Deck (1958) who induced limb regeneration in adult frogs by implantation of either fresh or killed tadpole
tissues, but not of agar. Interestingly, total trauma, as indicated by
severity of host limb tissue damage, was greater and more prolonged in
the agar implant experiments than in the fresh or killed tadpole tissue
implant series. Carlson and Morgan (1967) and Stevens et al. (1965) also
find that the extent of implant-induced trauma is not directly correlated
with limb induction and speculate that the promoter effect is mediated by
an as yet unidentified substance. As in limb regeneration, successful
accessory limb induction is realized only through the establishment of a
blastema. Stevens et al. (1965) point out that blastemal cell aggregation
occurs only when there is an intimate contact between the thickened
epithelium of the graft insertion wound and the histolizing mesodermal
tissues of the limb. It is, thus, interesting that in supernumerary limb
induction, as is also true for normal regeneration and for regeneration
evoked in the adult frog by trauma, there is consistently present a
thickened epidermal plate, or "wound epithelium," at the site of regenerative response. Further evidence of the importance of wound epithelium
for initiating blastema formation will be more fully discussed later
(Section II,B). For the present, the possibility that regeneration promoters, whether systemic or local in origin, influence regeneration by
activating the wound epithelium is a tempting speculation. Although
some chemical agents, such as beryllium nitrate, seem to act as nonspecific poisons and block regeneration at any phase, others act as antagonists of specific metabolites and inhibit specific phases of regeneration
with a high degree of precision (see Lehmann, 1961, for review). Further
work with these latter types of compounds may provide us with some of
the answers to the problem of the identity and specific mode of action of
the promoters of regeneration.
2.
Demolition
Amputation and wound healing are followed, within a few hours, by a
short period of tissue destruction which is called "demolition." Only the
distalmost injured ends of the cut stump tissues are affected, in the
larva for a period of only about 2 days but longer in the adult limb.
Blood cells, primarily phagocytes, migrate into the limb stump and
211
supernumerary limb induction by previously frozen newt kidney, compared to fresh newt kidney, but this inducing effect was destroyed by
boiling. Thus a protein would seem to be indicated. Also pertinent here
are the results of Malinin and Deck (1958) who induced limb regeneration in adult frogs by implantation of either fresh or killed tadpole
tissues, but not of agar. Interestingly, total trauma, as indicated by
severity of host limb tissue damage, was greater and more prolonged in
the agar implant experiments than in the fresh or killed tadpole tissue
implant series. Carlson and Morgan (1967) and Stevens et al. (1965) also
find that the extent of implant-induced trauma is not directly correlated
with limb induction and speculate that the promoter effect is mediated by
an as yet unidentified substance. As in limb regeneration, successful
accessory limb induction is realized only through the establishment of a
blastema. Stevens et al. (1965) point out that blastemal cell aggregation
occurs only when there is an intimate contact between the thickened
epithelium of the graft insertion wound and the histolizing mesodermal
tissues of the limb. It is, thus, interesting that in supernumerary limb
induction, as is also true for normal regeneration and for regeneration
evoked in the adult frog by trauma, there is consistently present a
thickened epidermal plate, or "wound epithelium," at the site of regenerative response. Further evidence of the importance of wound epithelium
for initiating blastema formation will be more fully discussed later
(Section II,B). For the present, the possibility that regeneration promoters, whether systemic or local in origin, influence regeneration by
activating the wound epithelium is a tempting speculation. Although
some chemical agents, such as beryllium nitrate, seem to act as nonspecific poisons and block regeneration at any phase, others act as antagonists of specific metabolites and inhibit specific phases of regeneration
with a high degree of precision (see Lehmann, 1961, for review). Further
work with these latter types of compounds may provide us with some of
the answers to the problem of the identity and specific mode of action of
the promoters of regeneration.
2.
Demolition
Amputation and wound healing are followed, within a few hours, by a
short period of tissue destruction which is called "demolition." Only the
distalmost injured ends of the cut stump tissues are affected, in the
larva for a period of only about 2 days but longer in the adult limb.
Blood cells, primarily phagocytes, migrate into the limb stump and