EVIDENCE FOR THE PRESENCE OF STEM CELLS IN THE TAIL OF THE MOUSE.

Summary In experiments in which the tails of mice were shielded during exposure to X-rays, colonization of the spleen occurred in excess of that found in whole-body irradiated control animals. This was the case whether the measure of effect was post-irradiative gain in spleen weight, uptake of IDU (5-iodo-2′-deoxyuridine), or nodule count. The degree of colonization was found to be a function of the length of time which elapsed between the original irradiation (with tail shielded) and a subsequent, suppressive irradiation of the tail. Histological examination showed that the spleen nodules were hemopoietic, and that normal tail vertebrae contained hemopoietic tissue.