While the term ‘microbiome’ was not coined until 1952, the discovery of gut microflora can be traced back to the nineteenth century. By the Fin de Siècle, medical professionals were aware of bacteria’s benefits for bodily health, and the influence of digestive disorders on mental health; this became widespread public knowledge in the first decades of the 1900s. This project examines the material and metaphorical role of the digestive system in British and North American popular fiction and cultural imagination from the 1870s to the 1930s. Popular fiction of this era, written for the mass-publishing market and with a huge number of readers, is overlooked in literary scholarship, yet it created new ways of relating to the digestive body and its unconscious processes. How did authors and characters understand themselves and the world through chewing, swallowing, digesting, stomach pain, indigestion, storage, and voiding? The project newly shows how digestive knowledge was ‘culturised’ through fiction, which integrated and challenged medical science, produced new digestive metaphors, and brought the gastrointestinal to bear on gender, class, and nationality. My hypothesis is that digestive organs and processes appear in these novels not only as an interest in the medical body, but also as impacting human emotions, instincts, and identity. This project contributes to literary and health humanities research scrutinising and shaping the narratives constructed around the microbiome.