Microglia-like Cells and their Reaction Following Injury to the Liver, Spleen and Kidney.

Certain cells in the nervous system which had hitherto been diicult to stain were induded by Cajal I in 1913 under the term "third element " of the central nervous system, and were suspected by him to be of mesodermal onrgin. Somewhat later del Rio-Hortega 25 was able to show that this "third element " consisted of two entirely different kinds of cells: one kind was the oligodendroglia of ectodemal origin; and the other kind he called microglia, the latter, in his opinion, being of mesodermal orgin. The central nervous system was made up, therefore, of neurones (the first element), neuroglia consisting of astrocytes and oligodendroglia (the second element), and microglia (the third element). Del Rio-Hortega's papers describing the microglia were published between I9I9 and 192I. Today del Rio-Hortega c believes, along with others, that the microglia represents the reticulo-endothelial system in the central nervous system. In 192I del Rio-Hortega and Jumenez de As6a7 demonstrated phagocytic cells in tumors, tuberrdes, liver lesions, normal human kidney, and in lymph follicles stained by silver carbonate. In this paper the authors drew attention to their belief that phagocytosis in the nervous system is the function of the micrglia and that the studies of del Rb-Hortega on the microglia constitute a concrete example of the general problem of the histogenesis of the macrophages. In 1927 Yimnnez de Asfia,' using silver carbonate, demonstrated Macrophages in a normal spleen and in tumors, and stated that in morphology, stain g properties and in function they resemble the microglia of the nervous system and, finally, that microglia cells are members of the reticulo-endothelial system. Cone,' in 1928, usng del Rio-Hortega's method for microglia, illustrated a phagocyte with a dose resemblance to transitional microglia in a degenerating area of a hypemephroma.