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Microscopic invaders were more of the threat nowadays. Just to name one example, there was Red Death, a.k.a. the Seven Minute Special, a tiny aerodynamic capsule that burst open after impact and released a thousand or so corpuscle-size bodies, known colloquially as cookie-cutters, into the victim's bloodstream. [...]
Such inventions had spawned concern that people from Phyle A might surreptitiously introduce a few million lethal devices into the bodies of members of Phyle B, providing the technically sweetest possible twist on the trite, ancient dream of being able instantly to turn a whole society into gravy. [...]
What worked in the body could work elsewhere, which is why phyles had their own immune systems now. The impregnable-shield paradigm didn't work at the nano level; one needed to hack the mean free path. A well-defended clave was surrounded by an aerial buffer zone infested with immunocules—microscopic aerostats designed to seek and destroy invaders. [...]
It was always foggy in the Leased Territories, because all of the immunocules in the air served as nuclei for the condensation of water vapor. If you stared carefully into the fog and focused on a point inches in front of your nose, you could see it sparkling, like so many microscopic searchlights, as the immunocules swept space with lidar beams. [...] The sparkling of tiny lights was the evidence of microscopic dreadnoughts hunting each other implacably through the fog, like U-boats and destroyers in the black water of the North Atlantic.
"""
Neal Stephenson, The Diamond Age
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