The question was how the macrophages knew what to attack and what to leave alone, which cells or particles were “normal” and which were deserving of destruction. Metchnikoff’s answer was essentially that macrophages, enjoying the “most independence” of any body cells, could decide this on their own2—protecting cells they recognized as belonging to the “self” and devouring anything else. This explanation was instantly rejected by most of Metchnikoff’s contemporaries. As philosopher Alfred Tauber writes, “The phagocyte [macrophage] as possessor of its own destiny and mediator of the organism’s
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