Pathological Study on the Marginal Zone of Spleen. - Electron Microscopic Observation on the Marginal Zone of the Mouse Spleen.

The marginal zone of the spleen was investigated by transmission electron microscopy in normal mice as well as in the mice injected with 4 test substances varing in size. The results obtained are as follows : 1. The marginal zone of the spleen has a characteristic structure, basically consisted of loose meshwork of long slender procsses of reticular cells accompanied with extracellular reticulum and form a narrow band surrounding a white pulp. Inner limit of the marginal zone is defined in some parts by marginal sinus. In regions not bordered by marginal sinus, outermost reticular cells of the white puIp form a discontinuous border. Outer limit of the marginal zone is not sharply difined. The marginal zone receives many arterial terminations from the white pulp via marginal sinus, the wall of which has many fenestrations facing the marginal zone. In the meshwork of reticular cells, medium sized lymphosytes and small lymphosytes are predominantly present and all kinds of circulating blood cells also exist, but there are a few macrophages and plasma cells. 2. The localization of saccharated iron oxide, carbon, latex, and horseradish peroxidase within the spleen is observed respectively at different periods following intravenous injection. In addition, the localization of the intraveously injected houseradish peroxidase is also investigated in the mouse which has been preimmunized with houseradish peroxidase. The results confirm that as far as the size of the injected particles are concerned, small particles pass through the marginal zone without stagnation and large particles stagnate for long in this zone.