In order to explore the ways knowledge travels across spatial and cultural boundaries, this article focuses on the intriguing case of the Edinburgh-trained Scottish surgeon James Esdaile (1808-59), who, after practising conventional surgery for almost fifteen years in British colonial India, quite unexpectedly turned to mesmeric anaesthesia in the last five years of his service. By following his career and his mesmeric turn, the article describes Esdaile's subsequent public experiments in mesmeric anaesthesia in collaboration with indigenous practices and practitioners of trance induction in the 1840s which led to the creation of a special mesmeric hospital in Calcutta. Although very successful, it eventually ceased to function, apparently victim to new and cheaper chemical anaesthetics. Mobilizing the insights of science studies scholarship into the processes of scientific experimentation, this article seeks to shed new light on the necessary professional, social and political investments for the making and mobility of scientific knowledge across social and cultural boundaries in a colonial setting.