Generally, the crux of the yin and yang is the yang qi is compact outside and the yin qi can then protect the inside firmly. If the yin and yang are disharmony, it is as if there is spring without autumn, and there is winter without summer. To harmonize the yin and yang is the policy of sages. If the yang qi is over-flourishing and fails to consolidate, the yin qi will be exhausted; if the yin and yang are in a harmonious balance, both essence and spirit will be normal; if the yin is severed from the yang, the essential qi will vanish.
Key Words: discussion of vital-qi corresponding to heaven, in the plain questions
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