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Circadian or Diurnal Cycle and other cycles
According to Chinese medical theory, each organ is associated with one of the Five Phases. It is believed to be more efficacious to treat an organ during a particular time period appropriate to it. The citation order of the Five Phases, i.e., the order in which they are cited in the Bo Hu Tong and other Han dynasty texts, is Metal, Wood, Water, Fire, and Earth. The organs are most effectively treated, according to theory, in the following four-hour periods throughout the day, beginning with the 3 a.m. to 7 a. m. period: Metal organs (see the list below), Earth organs, Fire1 organs, Water organs, Fire2 (the "non-empirical" Pericardium and Triple Burner organs), and Wood organs, which is the reverse of the citation order (plus an extra use of Fire and the non-empirical organs to take care of the sixth four-hour period of the day). These two orders are further related to the sequence of the planets going outward from the sun (Mercury, Venus, Mars, Jupiter, Saturn, or Water, Metal, Fire, Wood, and Earth) by a star diagram similar to the one shown above.