It may be concluded from these experiments that excessive doses of thyroid cause (a) moulting, followed by rapid regeneration of depigmented feathers in mature birds; (b) depigmentation of growing feathers followed by increased melanisation in young birds, giving a white and black bar; (c) accelerated growth rate in all feathers, regardless of the region considered or the age of the bird; (d) stimulation of the papilae of plucked feathers causing rapid regeneration from each papilla.

From the variability in the measurements recorded, liver feeding appears to have no definite effect upon feather growth, but a slight stimulating effect upon the papillae causing them to regenerate.

In cases of lack of external signs of regeneration of feathers for some months after plucking in normal or liver-fed birds, the papilla regenerates a rudimentary calamus, or lies quiescent beneath cornified tissue which acts as a calamus, until the next moult, or until some substance with an accelerating influence upon feather growth (e.g. thyroid) is administered.

This content is only available via PDF.