The dung bath appears in alchemical operational literature under the Latin name venter equinus, "horse's belly," as one of the standard named heat sources alongside the water, ash and sand baths, specifically associated with digestion, the slowest and gentlest stage of alchemical practice. Its documentation is thinner than the other baths in this group, and no single first describer can be verified for it; it reads in the surviving operational texts as an established, unremarkable part of the working vocabulary rather than as a named innovation, so any claim of a specific inventor here would be invented rather than sourced.
What can be said with confidence is that the underlying phenomenon is real: fermenting organic matter does generate heat, a fact anyone who has stood near a fresh compost pile or a working manure heap can confirm directly, so the dung bath's function does not depend on any alchemical theory being correct. It did not survive into the modern laboratory under its own name; low, steady, unattended heat is now produced electrically rather than biologically. The same microbial heat-generating principle, however, is put to deliberate modern use in composting and in some low-tech greenhouse and water-heating designs that warm a space or a tank using nothing but a large, actively fermenting compost pile.