The responses of some developing feathers to X-rays.

T H E work here to be described was undertaken in order to see, first, whether the treatment of feathers by X-rays would have an effect similar to that described for hair (Chase, 1949, 1951) and, if such an effect were found, then, second, to see whether the results could be more reasonably attributed to a direct effect on the colour-producing cells themselves rather than to an effect upon the epithelium the cells of which would normally receive the pigment. The colours in the normal feathers used are yellow and black, and these are, in the definitive feather, due to the presence of finely divided yellow melanin and black melanin in easily recognizable pillules. The melanin in each case is elaborated in pigmentproducing cells such as those shown in Plate 1, figs. A and C. In some colourproducing cells at the base of the normal neck-feather the pigment, which cannot be donated because the cells lack processes, is to be seen aggregated into relatively large masses giving the cell a mulberry-like appearance (Plate 1, fig. D), reminiscent of the condition seen in some melanomata (Plate 1, fig. B) where, again, the pigment apparently cannot be passed on. One of the objects of the investigation was to see whether these feathers, upon irradiation, showed recognizable changes in the distribution of yellow and black and whether the pigment-producing cells showed any abnormality in the physical condition of their contained pigment. It was also regarded as important to see whether any such effect would persist in a series of feathers from the same follicle.