Seasonal Variation in Thyroid Gland Activity in Deermice.

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Abstract
A seasonal difference was noted in thyroid gland activity in two sub-species of male deermice (Peromyscus mani-culatus bairdii and P. m. gracilis) maintained under constant laboratory conditions of temperature, light and food. Thyroid cell height and thyroxine secretion rates were at a maximum during December-March and a minimum during October for bairdii, and at a maximum during October-December and a minimum during March-July for gracilis. The percent colloid was highest for bairdii during October and for gracilis during July. I 131 uptake was maximum during December for both bairdii and gracilis. In general, the thyroid gland of bairdii was more active than the thyroid of gracilis throughout the year with the exception of October.