A. Formulation of the Problem and Relevant Literature -- I. โ{128}{156}Mononuclear Phagocyte Systemโ{128}{157} -- II. Literature Dealing with Mononuclear Phagocytes in the Central Nervous System -- III. Considerations on the Origin of Mononuclear Phagocytes in the Central Nervous System -- B. Authorโ{128}{153}s Investigation -- Materials and Methods Consistently Used -- I. Origin of Mononuclear Phagocytes of the Nervous System -- II. Mode of Distribution and Possible Lymphatic Efflux of Intracerebrally Injected Corpuscular Particles and Cellular Elements -- III. Functional Activity of Mononuclear Phagocytes of the Central Nervous System -- C. Discussion and Conclusion -- I. Explanation of the Authorโ{128}{153}s Findings -- II. Mononuclear Phagocytes of the Central Nervous System and the โ{128}{156}Mononuclear Phagocyte Systemโ{128}{157} -- III. Summary of the Authorโ{128}{153}s Investigations -- References