A 16th century Japanese medical text included illustrations of the mythical creatures that cause disease when they invade the body. Although the basic concept proved to be true, bacteria and viruses were not visible at the time. The fanciful depictions and descriptions are a hoot, considering what we know now! For example, Gyochu as pictured here.
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Gyochu, a deadly critter responsible for leprosy, acts as a messenger to the underworld. On the night of Koshin-no-hi (an important date occurring every 60 days on the Chinese calendar), Gyochu leaves the body to visit Enma-daio (Lord of the Underworld) and tell him of your misdeeds. Enma-daio is known to punish people for bad behavior by reducing their remaining time on earth.
See more at Pink Tentacle. Link -via Everlasting Blort