Abstract
Summary
(1) Fifty to 100 microcuries of radioactive iodine in the form of Nal were injected into the peritoneal cavity of the gestating hamster on the 8th to the 15th day after copulation. (2) Observations made on embryos of from 8 to 15 days of development by means of autoradiographic study and tests with the Geiger-Muller counter show that radioactive iodine begins to accumulate in the thyroid on the 13th day of development. (3) The accumulation of radioactive iodine is coincident with the appearance of discrete follicles, which first appear between the 12 th and 13th day of development. (4) The quantity of iodine-containing colloid increases with the number of follicles present and the age of the embryo.
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