Regeneration of Feathers after Thyroid Feeding

STUDIES of the regeneration of feathers after plucking show the existence of considerable differences in the time intervals before the commencement of regeneration in individual feathers. In normal moulting, the development of the new feather starts before the old feather is shed, and as growth of the new feather continues and it emerges from the follicle, it may frequently be seen projecting within the inferior umbilicus of its predecessor (Hosker, 1935). Experimental moulting (e.g. by thyroid feeding in excessive doses) merely causes an acceleration of this process. When, as is often necessary in assaying the effect of endocrine extracts upon plumage, whole areas are plucked in order to ascertain that the feathers will be in an actively growing condition when the extract is administered, it often happens that many feathers fail to regenerate at all. If near the normal moulting period when plucked, the new feathers usually regenerate immediately (the "pin feathers" showing within the first week), but at other seasons of the year regeneration may be delayed for months. It was decided, therefore, to examine the effect of some known accelerating substance on the rate of regeneration of plucked feathers, and also to compare the histological picture of feather germs which regenerated rapidly with those which had failed to regenerate for some time after plucking.