Abstract
This paper presents a preliminary report of an analysis of the effect of hypernormal concentrations of thyroxin upon an embryonic organ, the feather germ.
The writer has demonstrated previously 1 that the feather pattern of the guinea is formed by repetition of a pattern unit, a transverse row of spots, which recurs after the lapse of a definite period of time, constant for an individual bird. This pattern period may be calculated, and furthermore the beginning and the end of a period may be distinguished easily in a definitive feather or in a growing germ.
In the experiments to be reported, 10 guinea fowls, 5 males and 5 females, were injected with solutions of Squibb's crystalline thyroxin in single injections as well as double and triple injections separated by 4 to 9 days, the doses ranging from 2 to 6 mg. The birds weighed between 2 1/2 and 3 lbs. Juhn and Barnes 2 produced an area of abnormal black pigmentation in brown Leghorns with doses as small as 0.5 mg. Although the guinea is a smaller bird, doses of thyroxin 12 times as large as this failed to produce any analogous change in pigmentation. On the other hand, doses less than 12 mg. cause no molting in the brown Leghorn, 3 while in the guinea 4 mg. is sufficient to produce general molting. No sex differences were noted in the susceptibility of guinea feathers to thyroxin.
Comparison of large areas of feathers treated with 4 mg. of thyroxin with their predecessors and successors grown from the same follicles—subcutaneous injections of India ink identified individual follicles—showed that the thyroxin feathers broke more easily, that they were shorter, that they carried fewer barbs, and that they required a shorter time to reach maturity. The contour of the feathers was concave, due to shorter barbs in the affected region.
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