THE COLLECTION OF RADIOACTIVE IODINE BY THE HUMAN FETAL THYROID*

Abstract

THE age at which the human fetal thyroid begins to function has been a matter of speculation for many years. Certain approximate time relations in regard to function have been assigned on the basis of studies such as Gorbman's (1, 2) of the lower forms of animal life. In 1836 Jones (3) was perhaps the first to describe the microscopic structure of the human fetal thyroid. He found that the thyroid was beginning to form differentiated tissue in a fetus of 4½ months. Both Horcicka (4) and Podack (5) late in the nineteenth century observed that typical glandular structure did not appear until the fifth fetal month. In Cooper's (6) study of the human thyroid at various ages of intrauterine growth, she observed the beginning of follicle formation by the thirteenth week, but no colloid or secretion within the lumina until late in the fourth month of pregnancy. The more differentiated tissue containing colloid seemed to appear at the periphery of the thyroid. Observations by Norris (7) indicated that typical colloid does not appear until the embryo measures 60 mm. (C-R), or is approximately 12 to 13 weeks old.