Effects of temperature on papilloma growth in the newt, Cynops pyrrhogaster.

The effects of temperature on skin papillomas of newts (Cynops pyrrhogaster) were studied. Newts bearing these tumors were maintained for 30 weeks at 4 +/- 1 (S.E.), 10 +/- 1, 13 +/- 2, 25 +/- 1, and 30 +/- 1 degree. The diameters of the papillomas were measured externally. They decreased at 4, 25, and 30 degrees, and increased at 10 and 13 degrees. The effect of temperature on the tumor growth or regression began to appear from around the 10th week. Furthermore, when the temperatures were changed, it was possible to reverse the growth or regression of the tumors. Histologically, cell layers of the tumors became thin at 4, 25, and 30 degrees, but there were some differences between 4 and 25 or 30 degrees. The pigment layers became thick, and epidermal cells invaded dermal layer at 4 degrees, and clumps of cells separated from the surface of the tumors at 25 and 30 degrees. Mitotic indices were lower at 4, 25, and 30 degrees than in normal epidermis, but were about 3 times as high as normal tissue at 10 or 13 degrees. The relation between these results in the laboratory and seasonal fluctuations of these tumors in nature is discussed.