The sizes and frequency of the nuclear bodies were observed in cells of the thymic cortex, thymic medulla, lymph node, spleen and patch of Peyer of mice. The nuclear bodies are most often found in small lymphocytes (32.3 to 37.1%) of the lymph node, spleen and patch of Peyer, but very rarely in small lymphocytes of the cortex (4.4%) and medulla (14.5%) of the thymus. The bodies are also often found in mesenchymal and epithelial reticular cells, but are variable in occurrence. From the frequency and size of the nuclear body in cells of lymphocytic series, it is suggested that in thymic cortex, about a half of the small lymphocytes contain a small nuclear body, and in the medulla all small lymphocytes contain a small or a large body, and in the other lymphatic organs all of small lymphocytes include two or more large, grouped, nuclear bodies. The outer filamentous coat of the nuclear bodies is closely related with nucleolus. No nuclear bodies were found in the large lymphocytes and mitotic cells. Thus the relationship between morphological changes of the nuclear body and differentiation of lymphocytes has been discussed in this paper
