Woodcut from Tong ren shu xue zhen jiu tu jing (Illustrated Manual of Acupoints on the Bronze Man) by Wang Weiyi, published in 1443 (8th year of the Zhengtong reign period of the Ming Dynasty), illustrating the rules for acupuncture prohibition.
These rules are attested in the early medical classics Huangdi Neijing and Zhenjiu jia yi. They are graphically represented here in a diagram composed of four concentric circles. The prohibitions are established by an complex combinatory system, structured according to the phases of the moon, in which zi and wu (1st and 7th Earthly Branches) form the 'warp'and mao and you (4th and 10th Earthly Branches) the 'weft'. A certain flexibility was allowed in applying these rules, and it was not expected that they should be strictly adhered to in life-or-death situations.
