The Chinese count time in a cycle of 60 terms. The cycle is called the sexagenary cycle. en.wikipedia.org/wiki/Sexagenar…. Years, Months, days and hours are counted using it. Today is the 57th term of the cycle, 庚申. This day is associated with a rather interesting medical practice.
2. Now, of old, the Chinese believed in the existence of a spiritual parasites collectively known as the Three Corpses. These three corpses live in everyone's body, and they want nothing better than their host to die, so they can be freed.
3. To that end, on the 57th day of the sexagenary cycle, these three corpses 三屍 would leave their host's body, and report the misdeeds of their host to the allotter of lifespan 司命 in heaven. The allotter of lifespan would correspondingly deduct the host's life for his sins.
4. As length, the host (i.e. you or me ) would perish, and the three corpses would be free to wander about, stealing the offerings people have left for their ancestors.
5. However, there is an easy way of preventing this. The 3 corpses would only leave your body when you are asleep. If you stayed up for the whole of the geng-shen night, the three corpses would be unable to leave and report on your sins.
6. The practice also spread to japan, where the practice of staying up all night evolved into a kind of all night party involving chess etc. en.wikipedia.org/wiki/K%C5%8Dsh….
7. for more on the Chinese custom, see en.wikipedia.org/wiki/Three_Cor…. Michel Strickmann's Chinese Magical medicine has an extensive discussion on the 3 corpses. Campany's "To live as long as Heaven & earth" also has a transl, of the sect of 抱朴子 from which the above was taken.
8. BTW here is the relevant sect of the Baopuzi 抱朴子 fr which the above was taken; it is in 卷6. "又言身中有三屍，三屍之為物，雖無形而實魂靈鬼神之屬也。欲使人早死，此屍當得作鬼，自放縱遊行，享人祭酹。是以每到庚申之日，輒上天白司命，道人所為過失."zh.wikisource.org/wiki/%E6%8A%B1…
