Abstract
1. The iodine content of the thyroid of the sexually immature male fowl is lower than that of the thyroid of the sexually mature. The increase in iodine content is coincident with the attainment of sexual maturity as estimated by the histological picture of the testis. 2. In the case of the material used there was no indication of a sex dimorphism in the matter of iodine content. 3. The average percentage of iodine content of the thyroid of the bird is significantly higher than that of the mammal.