An acrasin is a pheromone used by species of slime mold, which signals to the many individual cells and triggers an aggregation response, such that they form a single large cell (a plasmodium). One of the earliest acrasins to be identified was cyclic AMP, found in the species Dictyostelium discoideum by Brian Shaffer, which exhibits a complex swirling-pulsating spiral pattern when forming a pseudoplasmodium.
The term "acrasin" is a reference to the character Acrasia in Edmund Spenser's Faerie Queene, who seduced men against their will and then transformed them into beasts. Acrasia is itself a play on the Greek akrasia that describes loss of free will.
