Histological Studies on the Functional Development of the Thyroid Gland of the Chick Embryo

I. Histochemical Observations

Abstract

1. In the normal chick embryo, the thyroidal colloid droplets appear at 9-10 days of incubation.
2. The thyroid gland obtains the latent function to make a colloid 8 days after the beginning of incubation, but, in this days old embryo the TSH (thyroid-stimulating hormone) content in the blood stream seems not to be sufficient to stimulate the gland.
3. The TSH injected at 4-7 days of incubation stimulates the gland to produce the colloid droplet at 8 days of incubation.