Electron Microscopic Observation of the Reticuloendothelial System.

Reticulum cells in the lymph nodes and the spleen, and histiocytes in the subcutaneous connective tissue were both studied with electron microscope. Reticulum cells showed marked development of endoplasmic reticules both rough and smooth varieties, and were classified with their fine structures into the mature, ingesting, immature and productive types. In the productive in flammatory lesions, the proliferation of the cell ensued from both mitotic division of the productive type and differentiation from the immature type and lymphoblast-like cells. Subcutaneous histiocytes had originally no or few rough surface endoplasmic reticula and well developed smooth surfaced ones. When the animal was sensitized or stimulated, however, histiocytes showed rather marked developing of rough surfaced endoplasmic reticula resembling the reticulum cells. These findings seemed to suggest the ability to synthesize some protein-like antibody. As for plasma cells, the most immature type showed a large nucleus with distinct nuceloli, and scanty cytoplasm with poorly developed endoplasmic reticula, rich free RNP granules and large mitochondria. The transformation from reticulum cells, however, were not observed in the lymph nodes.