AMPHIBIAN LIMB REGENERATION
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be able to identify blastemal cells with certainty throughout the entire
period of regeneration. The early experiments of Butler (1935) established the fact that the blastemal cells are of local origin. He transplanted unirradiated limbs of Ambystoma
larvae to X-irradiated hosts.
The irradiated limbs of the host were incapable of regenerating, but the
unirradiated limb on the irradiated host regenerated after amputation.
The blastemal cells could only have been derived from the transplanted limb itself and not from the body of the host. Later Brunst and
Cheremetieva (1936) and Butler and O'Brien (1942) demonstrated that
blastemal cells are derived from areas close to the amputation surface.
When a short midsegment of a larval urodele limb was exposed to X-rays,
subsequent amputation through this region was followed by failure to
regenerate. However, amputation just distal, or proximal, to the irradiated region stimulated normal regeneration. Experiments such as these
have localized the area of origin of blastemal cells in limb regeneration
but have not provided information on the tissue source of these cells.
The investigation of the tissue origin of the blastemal cells was given
new impetus, however, by the demonstration of inhibition of limb regeneration by X-rays. Could single limb tissues, transplanted to irradiated limb stumps, give rise to blastemal cells and organize a regenerate?
When this experimental design was put into effect (Umanski, 1937;
Thornton, 1942) it was found that such unirradiated limb tissues as
muscle, bone, cartilage, and skin (dermis with epidermis) when transplanted individually to irradiated limb stumps of urodeles would develop
regenerates in many cases. The assumption in these positive cases of regeneration was that the blastemal cells were derived from the unirradiated implants. This assumption has been questioned by Liosner (1947),
Sidorova (1949), Trampusch (1951, 1958a,b), and Blacher (1952). Thus
Trampusch, whose work is most extensive here, replaced skin of Xirradiated tails with unirradiated limb skin, and vice versa. Amputation
of the irradiated organ led to the formation of a regenerate with donor
morphological characteristics. An irradiated limb with unirradiated tail
skin, for example, regenerated tail-like structures. The conclusions
reached by Trampusch from these results were quite opposite to the conclusions of Umanski and Thornton. Trampusch speculated that irradiation destroys the "field" characteristics of the organ and that unirradiated tissue grafts restore regenerative ability in the irradiated organ by
re-establishing a "field." Since he has observed mitosis in irradiated limb
tissues he assumes that these irradiated tissues are capable of regenerating if a morphogenetic agent is present. However, these results of
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be able to identify blastemal cells with certainty throughout the entire
period of regeneration. The early experiments of Butler (1935) established the fact that the blastemal cells are of local origin. He transplanted unirradiated limbs of Ambystoma
larvae to X-irradiated hosts.
The irradiated limbs of the host were incapable of regenerating, but the
unirradiated limb on the irradiated host regenerated after amputation.
The blastemal cells could only have been derived from the transplanted limb itself and not from the body of the host. Later Brunst and
Cheremetieva (1936) and Butler and O'Brien (1942) demonstrated that
blastemal cells are derived from areas close to the amputation surface.
When a short midsegment of a larval urodele limb was exposed to X-rays,
subsequent amputation through this region was followed by failure to
regenerate. However, amputation just distal, or proximal, to the irradiated region stimulated normal regeneration. Experiments such as these
have localized the area of origin of blastemal cells in limb regeneration
but have not provided information on the tissue source of these cells.
The investigation of the tissue origin of the blastemal cells was given
new impetus, however, by the demonstration of inhibition of limb regeneration by X-rays. Could single limb tissues, transplanted to irradiated limb stumps, give rise to blastemal cells and organize a regenerate?
When this experimental design was put into effect (Umanski, 1937;
Thornton, 1942) it was found that such unirradiated limb tissues as
muscle, bone, cartilage, and skin (dermis with epidermis) when transplanted individually to irradiated limb stumps of urodeles would develop
regenerates in many cases. The assumption in these positive cases of regeneration was that the blastemal cells were derived from the unirradiated implants. This assumption has been questioned by Liosner (1947),
Sidorova (1949), Trampusch (1951, 1958a,b), and Blacher (1952). Thus
Trampusch, whose work is most extensive here, replaced skin of Xirradiated tails with unirradiated limb skin, and vice versa. Amputation
of the irradiated organ led to the formation of a regenerate with donor
morphological characteristics. An irradiated limb with unirradiated tail
skin, for example, regenerated tail-like structures. The conclusions
reached by Trampusch from these results were quite opposite to the conclusions of Umanski and Thornton. Trampusch speculated that irradiation destroys the "field" characteristics of the organ and that unirradiated tissue grafts restore regenerative ability in the irradiated organ by
re-establishing a "field." Since he has observed mitosis in irradiated limb
tissues he assumes that these irradiated tissues are capable of regenerating if a morphogenetic agent is present. However, these results of