Much of the American medical and scientific work on this topic appeared in the 1870s, which meant that its authors shared a common point of reference for mass psychic upheaval: the Civil War. For instance, Philadelphia physician and novelist Silas Weir Mitchell wrote about mental permeability and contagion in a decidedly negative light: if people could see each others' true thoughts, “the whole fabric of civilization would crumble”, one of his characters warned. During the war, Mitchell served in the Turner's Lane army hospital, where he studied the lingering effects of nerve injuries through intimate conversations with men who had actually seen civil society crumble around them and who had fought in its ruins. In his subsequent decades of practice, Mitchell urgently counseled patients and the public on shoring up their nervous power to defend against the intrusion of alien psychic forces. Though he denounced psychic mediums as frauds, Mitchell wrote so incessantly about mental barriers and scenarios of penetration that his concern about volatile powers of mind is unmistakeable. Perhaps, like Walt Whitman, another Civil War medic, Mitchell was plagued by “dreams’ projections”, sentenced each night to “thread my way through the hospitals”. What war reporter Ambrose Bierce called a “spiritual darkness”, unleashed over four years of brutal killing and halted only with fragile documents, left a generation wary of the violence lurking below the surface of American life.