Nineteenth-century physicians increasingly favoured leeching – the placing of a live leech onto a patient’s skin to stimulate or limit blood flow – as a cure for numerous ailments. As conviction in their therapeutic properties spread, leech therapy dominated European medicine; France imported over fifty million leeches in one year. Demand soon outpaced supply, spawning a lucrative global trade. Over-collection and farming eventually destroyed leech habitats, wreaked environmental havoc and forced European merchants to seek new supply sources. Vast colonies of leeches were found to inhabit the immense wetlands of the Ottoman Empire, which soon became a major exporter of medicinal leeches. Following the Treaty of Balta Liman (1838), the Ottoman state moved to exert control over the lucrative trade, imposing a tax on leech gathering and contracting with tax-farmers (mültezim) to collect the taxes. British diplomats, merchants and other stakeholders protested the imposition of the tax, as had previously happened with the commodification of wildlife; their pursuit of profit led collectors and farmers to over-gather leeches, with catastrophic consequences. By the end of the century, so great had their worth climbed that the leech population faced extinction. This paper situates medicinal leeches as therapeutic actors of history and adopts an interscale approach in formulating the human-leech interaction. It offers a substantive contribution to the history of medicine, in revealing the centrality of leeches to the rise of modern medicine and global trade, but also by making visible their role in shaping imperial diplomacy and worldwide economic markets.

Among the solutions devised by early modern Western European states to engage with the private sector in the governance of their overseas empires, the adjudication of revenue farms and colonial monopolies was often dismissed by historians on the grounds of being coercive, inefficient, and risk-exempt for the contractors. In reality, however, the threat of financial hardship and insolvency was very real, and not infrequently led to contractual removal, the seizure of collateralized assets, and even the imprisonment of the concessionaires.

This article approaches the neglected topic of failure in big business in early seventeenth-century Portugal, an overlooked case of a contractor state that relied extensively on the adjudication of government contracts to finance and rule its overseas empire. By looking into the downward trajectories of two tax-farmers and the collapse of their contractual dealings, light will be shed on how the Crown and private entrepreneurs reacted to the repercussions of failure in these early modern public-private partnerships. It will also be shown how the road leading to termination was very much shaped by the political relationships between the Crown and its contractors and can only be understood in the context of wider relationships of brokerage, credit, and service between the two.