On the Essence of Dragon and Tiger 龙虎精微论

The author is unknown. Judging from its content, it was presumably composed by a Taoist priest of the Internal Alchemy School between the Tang and Song dynasties.

Consisting of one scroll, it is included in the Zhengyi Section within the Daoist Canon (The Daozang).

On the Essence of Dragon and Tiger

This text expounds the Dao of Internal Alchemy. It holds that the path to cultivating the Golden Elixir must follow the principles of heaven and earth: taking the Qi of Yin and Yang and the Five Elements, as well as the essence of the sun, moon, and Four Symbols, as the alchemical medicines. The timing of the alchemical fire is determined according to the changes of Yin and Yang, cold and heat. When the dragon and tiger interact and the "husband and wife" (metaphors for complementary energies) unite, the Golden Elixir can be accomplished.

The author denounces external alchemy, which involves smelting substances such as sulfur and mercury, arguing that such practices can only produce pigments for painting—wasting time and resources to no avail. At the end of the text, ten poems are appended, singing the praises of Internal Alchemy theories. Additionally, The Fire Timing of Zhuangzi and Laozi is attached, describing methods of daoyin (guided movement) and Qi circulation.