Early modern chemotherapy made an enduring impact on the human body and on current practices of medical research. Contrary to the widespread myth that locates the origins of modern chemotherapy in the mind of man, this paper analyses its emergence from material assemblages comprising trypanosomes, dyestuffs, physicians, and nonhuman animals at the turn of the century. Anti-infective drugs were not the only bodies that arose from these complex meshworks – assemblages as bodies and bodies of assemblages shaped each other in “co-constitutive relationships” (Donna Haraway). Drawing on neo-materialist theory, this article cartographizes these productive assemblages on the basis of scientific papers by David Bruce and Paul Ehrlich/Kiyoshi Shiga. Finally, these texts are juxtaposed with an 1858 article by the missionary and physician David Livingstone to reflect on the contingency of the animal-human-relationship in medical science.