The Effect of Thyroxine and Iodinated Casein on the Development of the Chick Thyroid

Wheeler and Hoffman (1948) showed that the feeding of thyroprotein to hens at the rate of 0.02% produced chicks that had significantly enlarged thyroid glands at hatching time. This seemed of special interest in the light of the fact that the administration of thyroprotein to chicks or hens caused an involution of the thyroid, Wheeler, Hoffman and Graham (1948). One possible explanation for the enlargement of the thyroid gland in chicks from hens fed thyroprotein is that the hen deposits, in the egg, thyroid-active or other substances which in some way affects the undifferentiated pituitary and thyroid of the embryo in a manner which is different from its affect on the pituitary or thyroid of the chick or hen. The basophils of the pituitary, which may secrete thyrotrophin, are not present until after about 10 days of incubation, Payne (1946). The thyroid first appears as a gland on the 4th . . .