Abstract
1. Tritiated thymidine was injected into mice of pregnancy ages 6, 7, 8, 9, 10, 11, 14, and 17 days.
2. The incorporation of the thymidine into the tissues of the embryo, uterus and placenta were studied by the method of stripping film autoradiography.
3. Thymidine is incorporated into uterine cells at all stages. The greatest amount of uptake is effected by endothelial cells. Decidual cells show good uptake at the beginning, less later.
4. Embryonic tissues do not show any noticeable uptake until the ninth day, and then only in the outer membrane tissues of the trophoblast cells, giant cells and yolk sac cells.
5. On the tenth day incorporation occurs mainly in the blood and mesenchyme cells. On succeeding days more incorporation is found in other embryonic tissue. The nervous system does not incorporate the thymidine noticeably until the fourteenth day.