Effect of thyroxin upon the thyroid gland and the regeneration and pigmentation of hair in Peromyscus.

1. Thyroxin distended the follicles of the thyroid gland of Peromyscus. 2. Thyroxin increased the rapidity and extent of hair regeneration in mice from which half the hair on the back was removed. 3. The regenerated portion of the pelage contained fewer hairs than were removed; the smaller the type of hair the less complete was its regeneration. 4. Thyroxin did not affect the pigmentation of regenerated hairs.