Pigmentary Reaction in Rana Clamitans Larvae Following Treatments With X-Rays.∗

Incidental to experiments on the effects of x-rays on the sex-glands of Rana clamitans tadpoles, our attention was drawn to certain conspicuous changes in the dorsal skin, especially the formation of whirls by the epidermal melanophores preceding their disintegration. The animals, after being narcotized in a 1:10,000 solution of water-soluble anesthesin, were placed on water-soaked cellucotton and exposed to unfiltered x-rays. A Victor Snook unit, with a universal air-cooled broad focus Coolidge tube was used to produce x-rays of different qualities. In the normal skin we find 2 types of brown melanophores: first, the asterisk-shaped pigment cells of the stratum corium (Figs. 2 and 6c),† which are distributed evenly over the back and flanks of the larvae. To them is due the general slate color of the dorsal skin (Fig. 1). Secondly, we find the filiform melanophores of the epidermis (Figs. 4 and 6e). They exhibit a remarkable tendency to form aggregations thus giving rise to the characteristic black spots on the back of the clamitans tadpole. It is well known that the so-called experimental albinism obtained upon hypophysectomy is largely due to the extreme contraction of the epidermal melanophores. We describe here only 2 stages of the pigmentary reaction following x-ray treatment. In the first case 10 tadpoles, of 43-45 mm. body length, and 8-10 mm. hind leg length, were given 8 treatments of 92 kilovolts 5 milliamperes, at 10 inches from the cathode. The animals were exposed for 10 minutes every other day and killed 6 days after the last treatment. Towards the end of the treatment the previously round pigment dots become streaky or comma-shaped. Later they begin to converge towards one or several centers which most often are located in the scapular and pelvic regions (Fig. 3, 22 days after the beginning of treatment).