IODINE STUDIES: I. The Avidity of the Thyroid Gland for Various Iodine Compounds in Vitro.

The literature on the relation of iodine to the thyroid gland is extensive, and a comprehensive review of it is not presented in this paper. Excellent reviews exist. The older literature has been reviewed by Horsley (1), the more recent by Wells (2), Marine (3) and Rost (4). Reference will be made only to those observations relevant to the particular problem under consideration. It is now generally recognized that though the thyroid gland contains little or no iodine in utero (5), after birth it becomes the chief storehouse for this element. In the adult it contains approximately 2 mgm. per gram of dry substance (6). The quantity is much less during the first ten years of life and there appears to be no significant variations due to the sex of the individual (7). It is characterized by a marked disproportion between its importance in the human economy and the amount required for its functional purpose. An intake of approximately 500 mgm. a year suffices. With the exception of a minute portion which is in inorganic form or in combination with lipoids (8), all exists in organic form. Practically all of it is found in the "colloid" substance (9) of the thyroid gland, the cells containing negligible quantities. All the iodine may be dissolved out from the thyroid in physiological salt solution (10). Since Baumann's discovery, in 1896, that the chief active ingredient of the colloid is an iodine containing compound, very little has been advanced as to the various chemical compositions in which iodine may exist in the gland, with the exception of the identification of thyroxin (11).