Abstract
The capacities for removal of inorganic iodine from the blood stream and for storage of such iodine in organic form in relatively high concentration are well known properties of the adult thyroid gland. The recent use of “tagged'radioactive iodine has provided the tool for the striking, graphic demonstration of these properties of the thyroid. 1 The accumulation of administred radio-iodine in thyroid tissue was revealed by these workers by placing sections of tissue in contact with X-ray films.
Using this method for revealing accumulated iodine, an experiment was devised to show at what stage of differentiation of the thyroid gland the ability for storage of iodine could first be demonstrated. Sixty-three tadpoles of the frog, Hyla regilla, were placed in a glass container in 800 cc of tap water. To this water was added an amount of radio-iodine,∗ as the sodium salt, which had a total activity of 150 microcuries. The preparation used has a half-life of 8 days. The mass involved was less than 0.1 mg.
The tadpoles, which were of all sizes from the just-hatched 7.0 mm larva to the 38 mm larva with well developed hind limbs (5.0 mm long) were kept in the radio-active water for 2 days. Most of the animals were fixed in formalin and serially sectioned. The lower jaws of the remaining tadpoles were dried on glass slides. Radio-autographs were made of the whole lower jaws, and of the serial sections by allowing the glass slides bearing them to remain in contact with a sensitive “no-screen”X-ray film. The serial sections were then stained in hematoxylin-eosin for matching with the radio-autographs. The staining properties of the tissues were slightly, but not seriously, impaired by the drying and handling incident to making the radio-autographs.
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