1. In a series of 10 male albino rats of the Wistar strain weighing aproximately 200 g each, total cellular number and cellular density in the thymolymphatic organs were estimated chemically by determining DNA-P content of the whole tissue and of each nucleus, using the Schneider method and diphenylamine test.
2. The values obtained for total nucleated cells in the lymphoid organs were as follows: (763±121)×10⁶ in the mesenteric lymph nodes; (1,165±79)×10⁶ in the other lymph nodes; (1,094±144)×10⁶ in the thymus; (1,375±189)×10⁶ in the spleen; (420±33)×10⁶ in the Peyer's patches; and (4,823±234)×10⁶ in the whole thymolymphatic organs.
3. The proportion of lymphocytes to total nucleated cells in imprint preparations was found to be: 89.7±2.0% in the mesenteric lymph nodes; 88.5±2.3% in the other lymph nodes; 97.9±0.4% in the thymus; 80.7±1.5% in the spleen; and 91.0±1.0% in the Peyer's patches.
4. The number of total lymphocytes was calculated to be.: (684±123)×10⁶ in the mesenteric lymph nodes; (1,031±106)×10⁶ in the other lymph nodes; (1,071±145)×10⁶ in the thymus; (1,100±169)×10⁶ in the spleen; (382±34)×10⁶ in the Peyer's patches; and(4,268 ± 577) x 106 in the whole thymolymphatic organs. It was estimated that the lymphocyte reserve in the whole thymolymphatic organs is 32 times as, great as the number of lymphocytes present in the circulating blood.
5. The estimated figures far total nucleated cells per 1mm³ of tissue (cellular density) were as follows: (1.92±0.15)×10⁶ in the mesenteric lymph nodes; (1.15±0.06)×10⁶ in the other lymph nodes; (2.68±0.27)×10⁶ in the thymus; (1.49±0.13)×10⁶ in the spleen; and (1.57±0.15) in the Peyer's patches. Thus, the cellular density is highest in the thymus and it decreases in the following order: mesenteric nodes, Peyer's patches, spleen, lymph nodes other than the mesenteric nodes.
6. On the basis of the figures obtained, a renewed calculation was made of the daily rate of production of lymphocytes by mitosis in the whole thymolymphatic organs.