Alchemy
Alchemically, the ouroboros is also used as a purifying glyph. Ouroboros was and is the name for the Great World Serpent, encircling the Earth.
The word Ouroboros is really a term that describes a similar symbol which has been cross-pollinated from many different cultures. Its symbolic connotation from this owes to the returning cyclical nature of the seasons; the oscillations of the night sky; self-fecundation; disintegration and re-integration; truth and cognition complete; the Androgyny; the primeval waters; the potential before the spark of creation; the undifferentiated; the Totality; primordial unity; self-sufficiency, and the idea of the beginning and the end as being a continuous unending principle.
Ouroboros represents the conflict of life as well in that life comes out of life and death. 'My end is my beginning.' In a sense life feeds off itself, thus there are good and bad connotations which can be drawn. It is a single image with the entire actions of a life cycle - it begets, weds, impregnates, and slays itself, but in a cyclical sense, rather than linear.
Thus, it fashions our lives to a totality more towards what it may really be - a series of movements which repeat. "As Above, So Below" - we are born from nature, and we mirror it, because it is what man wholly is a part of. It is this symbolic rendition of the eternal principles that are presented in the Emerald Tablets of Thoth.