Mellon MS 110: Alchemical and Rosicrucian compendium (selected pages). Unsigned, ca. 1760. Beinecke Library, Yale.
f. 225v : Ouroboros/the Three Essentials (Tria Prima, Mercurius) within the alchemical cosmos. f. 226r: The unified Solar King and Lunar Queen (conjunctio) conquer the dragon (prima materia, also Mercurius).
Slaying of the dragon is a metaphor for the conscious ego regressing back to the prima material (the instinctual core of the being). The terrible dragon, frog, or other form represents the Shadow or unknown aspects of self. These qualities need to be understood, to bring humility and wisdom to the transforming consciousness. After the dragon is slain, the King and Queen (conscious ego) can re-orientate itself, aligning to the newly discovered aspects of Self. The journey into Darkness is key to the breaking down of the immature Ego.