The aim of this paper is to explore how the cosmic soul works and how it accomplishes its providential and demiurgic tasks in Chrysippus’ system. Drawing on (i) the analogy Chrysippus establishes between the individuum and the cosmos and (ii) biological and medical theories of respiration, digestion, and pulse, I will show that the movements of Chrysippus’ cosmic soul reproduce the processes of digestion, pulse, and respiration at a cosmic level. My claim is that Chrysippus, in addition to adopting Praxagoras’ (...) notion that inhaled air nourishes pneuma—well established in the scholarship—appropriated Aristotle’s complex mechanism of respiration and digestion based on the teleological role of cold air, crucial for preserving vital heat. So understood, Chrysippus’ application of biological notions to cosmology allows him to endow the active principle with effective causation throughout the cosmos. (shrink)