[lymphoid organ pulsation].

Intact mice showed circadian rhythms of changes (pulsations) in the weight of the lymphoid organs, in the number of nuclear cells, as well as in the activity of serum factor(s) modifying lymphocyte migration in vitro. The pulsations were manifested by a short-term (over 1-4 h) twofold increase in the weight of the thymus, spleen and lymph nodes and in the number of cells contained by these organs. Sera from the animals with the enlarged organs inhibited the migration of thymocytes and spleen cells in vitro. The increased migration followed the maximal weight and the maximal number of cells of the lymphoid organs. It is suggested that pulsations seen in the lymphoid organs might reflect the mechanism of lymphocyte recirculation monitored by humoral mediators.