The origin of Daoyin

Take a deep breath and sink it to dantien. Hold the breath there for a while and then exhale it like the sprouting off grass until the it goes to the top of your head. In this way, the yang vital energy go up and the yin down. Those whose yang or yin energy goes its own way will live, otherwise they will die.

(Inscription from a Warring State Period cultural relic)

Reference:
Datan Qigong
by Yang Meijun, Heifeng Publishing Co. fifth edition 2000
ISBN: 9622381847