This article examines health, human–animal relationships and environments within nineteenth-century France, focusing on Hirudo medicinalis, the medicinal leech. Drawing upon medical, environmental and ‘more than human histories’, we investigate how a ‘mania’ for bloodletting in the wake of Parisian medicine and what Michel Foucault has characterised as the ‘birth of the clinic’ produced a trade in leeches that threatened to push the species to extinction. While urban-educated naturalists, physicians, pharmacists, merchants and politicians worried over the scarcity of what was widely considered a commodity of national economic and medical importance, rural ‘leech gatherers’ quietly developed ways to breed leeches artificially. The outcome was hirudiculture: the farming of leeches on an industrial scale. We argue that the birth of hirudiculture was more than a practical and commercial response to the needs of medicine; it reflected and embodied similar shifts in knowledge and reveals the complex and diverse ways in which rural and urban environments, human and non-human relationships, have shaped each other in the pursuit of shared visions of health.