Laboratory Hosts: Postcolonial Parasites, Growth Factors, and the Fabrication of a Molecular Gaze

From the final decades of the nineteenth century onward, physicians and scientists trained in Europe’s colonial powers devoted considerable attention to the lives of parasitic organisms found in the bloodstreams of humans and other animal hosts. Initially, this work required direct access to blood freshly sampled from a host and was spurred by desires to reduce the incidence of so-called tropical diseases such as malaria and sleeping sickness, which were especially prevalent in parts of the world that European powers had claimed as colonies. Soon, noting the successes of bacteriologists in cultivating pathogenic bacteria in sterilized glass containers, some researchers set out to domesticate parasitic protozoa, as well. By the early twentieth century, these investigators had codified recipes for culturing a range of blood parasites, dramatically increasing the mobility of these organisms between colonial and metropolitan laboratories. This essay explores a handful of the many meanings that researchers attached to parasites in vitro. As pathogens, these organisms stubbornly confounded colonial campaigns to staunch their spread between human and animal hosts, yet as laboratory organisms, they posed timely and tractable intellectual puzzles, such as how molecularly defined nutrients functioned in the broader metabolic contexts of living cells. This essay traces a genealogy of experimental practices that gave rise to laboratory hosts. By mimicking or supplanting the functions of living hosts’ bodies, laboratory hosts transformed blood parasites into experimental tools. In time, they additionally came to incorporate synthetic and manufactured ingredients, further alienating parasites from their former dependencies on hosts’ blood. Through these nutritional negotiations, researchers reimagined specific biological relationships as generic chemical ones, thus rendering parasites viable models of metabolic processes unfolding in a great many living things. While eliciting skepticism from some commentators, such chemical views of nature’s order grew enormously influential in midcentury biology and medicine. In examining a selection of the materials and techniques that made up laboratory hosts, this essay illuminates significant yet overlooked continuities between the practices of colonial era tropical medicine and postwar molecular life science.