ABSTRACT
Doses of up to 1,000 r. of X-rays administered to a patch on the back of the neck of Brown Leghorn capons had no permanent effects on either the structure or the colours of the feathers subsequently produced in the patch.
A dose of 2,000 r. was followed by a marked and permanent loss of colour, but no recognizable structural abnormalities, beyond a slight reduction in size, in the feathers subsequently produced in the patch.
The immediate response of an actively growing feather-germ to a dose of 2,000 r. was closely comparable with its known response to traumatic treatment such as cauterization. It can be understood as an abnormal and local moult.
Feathers growing in the patch after a dose of 2,000 r., if they had colour at all, had it mostly at their distal ends. Series of feathers which were white with coloured tips were produced from identified follicles.
The irradiation appears to have affected the physiological situation of the feather-germs in such a way as to forbid the melanocytes, though present and potentially functional, to enter the ectoderm in the normal way and to donate pigment. The melanocytes in these abnormal circumstances fail to develop normal processes. The melanin in them is in an abnormal physical state of aggregation. This condition is also to be seen in the non-donating ‘mulberry cells’ and in the coloured elements of some melanomata. This effect is probably due to a change in the ectoderm, but this change must be of a most restricted character since it does not interfere with the capacity of the ectoderm to produce structurally normal feather. Its nature is not yet understood.