"Mysterious Pearls"( 玄珠 xuanzhu ) is a term of the science of the Golden Elixir ( 金丹 jindan ). This term was originally used in philosophy and first found in the chapter "Heaven and Earth" ( 莊子 zhuangzi ) in the Book of Master Zhuang ( 黃帝 huangdi ). According to this chapter, the Yellow Emperor lost the "mysterious pearls" when traveling to the north of the Chishui River and climbing the Kunlun Mountain. Since he cherished the "mysterious pearls" very much, the Yellow Emperor had "Zhi" and "Lizhu" look for them but failed. At last, he sent Wang Xiang for it, and the latter finally found them. What on earth do the "mysterious pearls" refer to? According to Sima Biao, "mysterious pearls" are the "Dao", or the "truth of the Dao". Then why did Wang Xiang manage to get back the "mysterious pearls"? What counts is the unconsciousness of the form. "Wang Xiang" is a metaphorical name. "Xiang" indicates the form, and "Wang" is interchangeable with "no", so "Wang Xiang" means without form. The reason why one can be formless is that there is no form in his mind. If the mind is empty, the "Dao" manifests itself spontaneously. In the Book of Master Zhuang, the pursuit of "mysterious pearls" has an abstract meaning. In Daoism, however, it signifies a high level of the attainment of Dao and is related to specific methods of Nourishing Life ( 養生 yangsheng ). Daoists attach great importance to "mysterious pearls". There are many writings concerning "mysterious pearls" in the Daoist Canon ( 道藏 daozang ) , such as the Records of Mysterious Pearls ( 玄珠錄 xuanzhu lu ), the Rhythmic Formula of the Mysterious Pearls ( 玄珠歌 xuanzhu ge ), the Commentary on the Mind Mirror of the Mysterious Pearls ( 玄珠心鏡注 xuanzhu xinjing zhu ), and the Secret Instructions of the Mysterious Pearls of the Six Vital Breaths from the Fundamental Questions (of the Inner Classic of the Yellow Emperor ( 素問六氣玄珠密語 suwen liuqi xuanzhu miyu )) . Though varied in the way of expression, these books are all concerned with the "mysterious pearls" obtained by Wang Xiang related in the book of Zhuangzi. But Daoism also gives this term a sense in terms of alchemical cultivation, so that "Mysterious Pearls" becomes a metaphorical expression of the Golden Elixir. On the one hand, it designates "sulphur and mercury" in Outer Alchemical ( 外丹 waidan ) refinement; on the other hand, it is a metaphor in Inner Alchemy ( 內丹 neidan ), which refers specifically to the fusion of the "Yin breath" in the liquid of heart (as shown by the trigram Li, which comprises two outer Yang hexagrammatic lines and one Yin inner hexagrammatic line) and the "Yang breath" in the essence of kidneys (as shown by the trigram Kan, which comprises two outer Yin hexagrammatic lines and one inner Yang hexagrammatic line).