1. In an experimental system of implant-induced supernumerary limb formation in the newt, two inhibitors of limb regeneration, X-rays and beryllium nitrate, were individually applied to either the frog kidney implants or to the host limb. 2. Kidney implants irradiated with 2,220 r or 3,000 r induced normal percentages of supernumerary limbs whereas normal implants placed into limbs previously irradiated with 2,000–4,000 r did not stimulate any supernumerary growth. 3. Implants soaked in N/7 beryllium nitrate for two minutes stimulated normal percentages of supernumerary growth, but, when normal implants were placed into beryllium-treated limbs, no regenerative response was noted. 4. Neither X-irradiation nor beryllium nitrate inactivate the ‘factor’ in frog kidney which induces supernumerary limb formation. When host limbs were treated with these inhibitors, dedifferentiation was blocked and a regenerative response did not occur despite the presence of an adequate stimulus in the form of the kidney implant. It is concluded that these inhibitors disrupt some phase of the process occurring between the initial stimulus and the onset of overt dedifferentiation.
The object of this experiment was to determine the anatomical distribution of a supernumerary limb-inducing factor in the tissues of adult Rana pipiens. One mm3 pieces of frog tissues (esophagus, stomach, duodenum, colon, ovary, oviduct, lung, spleen, fat body, cardiac muscle, brain, skeletal muscle, peripheral nerve, skin and tarsal phalanges) were implanted subcutaneously in 252 upper arms of newts (Triturus viridescens). Results of these and previous experiments show that tissue from the lung and the urinary tract possess the greatest ability to induce supernumerary limbs. This ability is moderately present in tissues of the digestive tract, the female genital tract and in skeletal tissues. It is absent in brain, skeletal and cardiac muscle, skin, peripheral nerves and liver.
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