Pattern Analysis in Plumage. III. Action of Thyroxin in High Concentrations

Abstract

The sequence of response of the components of the definitive feather to increasing thyroxin concentrations—blanching of barbs, barbule formation, and pigment deposition—and the manner of estimating barb growth in the germ by observation of the order of appearance of pigment following injection of thyroxin have been established by Lillie and Juhn. 1

An examination of definitive feathers subjected to heavy thyroxin dosages (10 mg., single injection) during development shows that both barb frequency and barb lengths are markedly altered. Barb frequency increases to a level around twice the barb frequency of a normal feather; a sudden drop then occurs to a level below that characteristic of barb frequency for the same region of the control feather. Barb length decreases following injection of thyroxin, then gradually returns to normal or possibly greater than normal length.

These relations are shown in the accompanying graph. The curves are for single longitudinal vane-halves of modified and control neck feathers. Distances from origin of rhachis are given in centimeters on the horizontal axis. Figures on the left ordinate refer to barb frequency, i. e., the number of barbs per millimeter rhachis length. Figures on the right ordinate apply to barb lengths.