FURTHER STUDIES OF A LYMPHOCYTIC HEMOGRAM AND ITS RELATION TO LYMPHOCYTOPOIESIS : Ⅰ. VARIATIONS IN MITOCHONDARIAL CONTENT IN BLOOD LYMOHOCYTES IN RELATION TO THE POSTNATAL DEVELOPMENT OF THE LYMPHATIC APPARATUS IN THE RAT

1. In the normal course of the postnatal development of lymphoid organs in the rat, a remarkable transient elevation of the average number of mitochondria was observed in circulating lymphocytes, during the period between 2 weeks and 2 months after birth. 2. This period concides with the period during which the processcs of new formation and differentiation of Flemming's secondary nodules proceed in the mesenteric lymph nodes and splenic white pulp, the former in particular. After maturation of Flemming's nodules in these organs has been accomplished, the mitochonrial number in circulating lymphocytes considerably fell and did not rise again. 3. These findings agree fairly well with the previous observation by Osogoe et al. (1953) and Awaya (1956) on rabbits and provide further evidence to indicate that a marked rise in mitochondrial number in blood lymphocytes takes place as a consequence of extensive new formation of Flemming's secondary nodules which, in turn, indicates an increased production and delivery of lymphocytes from the lymphoid organs.