Abstract
1. Lymphocytes of smaller size were constantly found in relatively large numbers in the epithelial layer of the villi of small intestine, not only in normal mice but also in those fasted for a long period (3-5½ days) and in those irradiated with a large dose of X-rays (400-1,000 r) on the whole body.
2. The overwhelming majority of lymphotytes were in the deeper portion of the epithelial layer, between the nucleus and the basement membrane.
3. In mice fasted for 5½ days and in those exposed to X-irradiadon in doses greater than 400 r, there was a significant increase in the number of lymphocytes in the epithelial layer of the villi, in sharp contrast to a marked reduction in the mitotic acticity of the cryptcells, as compared with normal mice.
4. The results are discussed in relation to the rapid renewal of the villous epithelium, which takes place as a result of intensive mitotic activity of the crypt-cells.
