Scanning electron microscope studies of lymphatic tissues with special reference to the structure of the reticulum.

Reticular cells of the lymph nodule in the rabbit appendix and the lymphatic pulp including the germinal center in the dog mesenteric lymph node were observed under the scanning electron microscope after removal of free cells. Three dimensional architecture and arrangement of the reticular cells varied by regions in the lymph nodule. The appendix lymph nodule encapsulated with the endothelium of lymphatic sinuses was subdivided into two regions: (1) a central region of sparsely arranged stellate cells with coarse processes and (2) a peripheral zone of densely arranged stellate cells with many delicate processes. In the lymph node, the germinal center contained a loosely formed network of delicate stellate cells. Peripheral reticular cells of the nodule were thread-like, extending concentrically around the germinal center or along the sinus wall. Many lateral bridges of the threads occurred segmentally. The reticular framework of the medullary cord formed spongy meshes by anastomoses of stellate cells. Cytoplasmic perforations were observed in the sinus wall of the medullary cord. Those may be for lymphocyte migration.