The action of x‐irradiation on the regeneration field of the forelimb of the adult newt, Diemictylus viridescens,

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Abstract
Studies were conducted in order to determine the nature of the action of x‐irradiation on regeneration of the urodele forelimb. Right and left forelimbs of adult newts were parabiosed along their posterior edges, after the right limbs had been irradiated with 2,000 r. Forelimbs of control animals underwent similar operations. However, both limbs remained unirradiated. The angles which the stumps made with each other were classified as parallel, acute, and wide angles. Sixty days after amputation of these limbs, the cartilage patterns of the two groups were compared. In the control series, as the angle between the stumps was increased, the number of digits in the bilaterally symmetrical regenerates decreased, with a loss of central structures. At very wide angles, the doubled stumps produced no regenerates. In the experimental series, there were no interference effects from the irradiated right forlimbs. Single normal asymmetric left hands regenerated, despite widening angles between the stumps. Sham operations, which were performed on irradiated and unirradiated limbs, seemed to have no effect on the regenerative capacities of the limbs, with no regeneration in 97.7% of the irradiated limbs and normal regeneration in 91.1% of the unirradiated limbs. X‐rays seem to act on the limb to eliminate the interference effects normally found in regenerating doubled stumps. This seems to involve a disruption of the longitudinal control of the regeneration field. The loss of inter‐tissue communication and possible loss of the bioelectric field is discussed.