216
CHARLES S. THORNTON
Trampusch are interpretable equally well according to the simpler
hypothesis that the graft provides both organizing activity and cellular
contributions. Stinson (1964a) has also found many mitoses in Xirradiated newt limbs but finds that they are atypical and daughter cells
produced by such mitoses are short-lived. Skowron and Roguski (1958)
have approached this problem by way of injecting homogenates of viable,
dissociated cells of axolotl limb or tail tissues into irradiated hind limbs.
The major cellular sources used were muscle and connective tissue. Limb
regenerates developed on the amputated, irradiated hind limbs which
received viable limb cells; tail regenerates formed on irradiated hind
limbs which received viable tail cells. The organ specificity in these
experiments is impressive and led to the conclusion that dissociated cells
provided both organizing activity and cellular contribution.
In recent years, Stinson (1963, 1964a,b,c) has devoted considerable
attention to the problem of whether unirradiated limb tissues of urodeles
can reverse the irradiation-induced inhibition of limb regeneration. He
has found that X-irradiated (4000 r) forelimbs of newts regenerate well
after receiving complete forearm regenerate autografts. The regenerates
display asymmetries corresponding to those imposed experimentally on
the autografts (reverse A-P polarity; longitudinal half-grafts; forearm
grafts to upper arm hosts) while control limbs, given similar exposures to
irradiation and provided with irradiated
autografts, or traumatized
severely, failed to regenerate. A particularly significant experimental design, however, was the implantation, as described above, of unirradiated
homografts
(limb regenerates from other newts) into irradiated limb
stumps. In these cases, regenerates the asymmetry of which corresponded
to that of the homograft formed on the irradiated limb stumps but
eventually regressed, presumably as a result of a delayed immunological
reaction common to the newt, This is precisely the sequence of events one
would expect if the cells of the regenerate were derived from the homograft and not from the host limb tissues.
Recent work of Polejaieff and his associates has, however, produced
results which have again raised the question of a reversal of the X-ray
inhibition of limb regeneration. Subcellular fractions of homogenates of
killed mammalian and amphibian tissues are reported to restore regeneration when injected into X-irradiated axolotl limbs (Polejaieff,
1959, 1960; Polejaieff et al, 1960, 1961). Repeated amputations were
necessary in order to evoke regeneration in these limbs and irradiated
control limbs also regenerated in significant numbers after repeated amputations, indicating that either spontaneous recovery occurred or that
CHARLES S. THORNTON
Trampusch are interpretable equally well according to the simpler
hypothesis that the graft provides both organizing activity and cellular
contributions. Stinson (1964a) has also found many mitoses in Xirradiated newt limbs but finds that they are atypical and daughter cells
produced by such mitoses are short-lived. Skowron and Roguski (1958)
have approached this problem by way of injecting homogenates of viable,
dissociated cells of axolotl limb or tail tissues into irradiated hind limbs.
The major cellular sources used were muscle and connective tissue. Limb
regenerates developed on the amputated, irradiated hind limbs which
received viable limb cells; tail regenerates formed on irradiated hind
limbs which received viable tail cells. The organ specificity in these
experiments is impressive and led to the conclusion that dissociated cells
provided both organizing activity and cellular contribution.
In recent years, Stinson (1963, 1964a,b,c) has devoted considerable
attention to the problem of whether unirradiated limb tissues of urodeles
can reverse the irradiation-induced inhibition of limb regeneration. He
has found that X-irradiated (4000 r) forelimbs of newts regenerate well
after receiving complete forearm regenerate autografts. The regenerates
display asymmetries corresponding to those imposed experimentally on
the autografts (reverse A-P polarity; longitudinal half-grafts; forearm
grafts to upper arm hosts) while control limbs, given similar exposures to
irradiation and provided with irradiated
autografts, or traumatized
severely, failed to regenerate. A particularly significant experimental design, however, was the implantation, as described above, of unirradiated
homografts
(limb regenerates from other newts) into irradiated limb
stumps. In these cases, regenerates the asymmetry of which corresponded
to that of the homograft formed on the irradiated limb stumps but
eventually regressed, presumably as a result of a delayed immunological
reaction common to the newt, This is precisely the sequence of events one
would expect if the cells of the regenerate were derived from the homograft and not from the host limb tissues.
Recent work of Polejaieff and his associates has, however, produced
results which have again raised the question of a reversal of the X-ray
inhibition of limb regeneration. Subcellular fractions of homogenates of
killed mammalian and amphibian tissues are reported to restore regeneration when injected into X-irradiated axolotl limbs (Polejaieff,
1959, 1960; Polejaieff et al, 1960, 1961). Repeated amputations were
necessary in order to evoke regeneration in these limbs and irradiated
control limbs also regenerated in significant numbers after repeated amputations, indicating that either spontaneous recovery occurred or that