Into the water in which larvae of amphibia were bred, 2.05μC/cc of I131 or 1.70μC/cc of P32 was placed, and change in histological picture of the thyroid was observed consecutively.
1) The course of change ill the thyroid gland was as follows : In the first place, cytoplasm of epithelial cells became granular or vacuolated, followed by atrophy of nuclei, and finally follicular structure was destroyed. In this stage, connective tissue, that is, stroma, in the periphery of the gland began to be proliferated, and it gradually spread towards the center.
2) The effect of isotope was not uniform on all the follicles, and degenerations of mild, medium and high degree were mixed.
3) Upon the thyroid, effect of P32 was generally milder than that of I131.