Quantiative Studies on the Rate of Cell Production in the ThymolymphaticOrgans. Ⅱ. Estimation of the Daily Mitonic Activity in Young Adult Albino Rats

1. Using male albino rats of the WISTAR strain weighing around 200 g, a series of quantitative measurements on the mitotic activity in the thymolymphatic organs have been made, with the aim to make possible a calculation of the total number of lymphocytes produced by mitosis per day in the thymolymphatic system. Mitotic counts were performed after suspensions of cell nuclei had been prepared from the thymolymphatic organs according to the technique described in the preceding paper (ITO, 1959). 2. Normal values of the mitotic index were found to be 1.13±0.06% in the thymus, 0.79±0.06% in the mesenteric lymph nodes, and 0.75±0.06% in the other lymph nodes. 3. The total percentage of mitoses per day in each of the thymolymphatic system was estimated to be 22.23±0.77% in the thymus, 7.85±0.37% in the mesenteric lymph nodes, and 6.65±0.26% in the other lymph nodes. These figures 6-hour periods so as to cover a total of 24 hours. 4. Using the data of MONDEN (1958 a) on the total number of lymphocytes contained in the thymolymphatic organs, the average number of excess mitoses of lymphocytes in the whole thymolymphatic organs was calculated to be 432 × 106. This is 3.3 times as great as the number of total lymphocytes present in the circulating blood. 5. By a direct calculation from the figures obtained for the daily mitonic rate, the turnover time of the lymphocytes in each organ of the thymolymphatic system was estimated to be 4.5 days in the thymus, 12.8days in the mesenteric lymph nodes, and 15.0 days in the other lymph nodes. 6. Besides, an indirect calculation of the turnover time was made from HOFFMAN' s formula, assuming that the mitotic time of diving cells in the thymolymphatic tissue is of 1-hour and of 30-minute duration.