With the increasing popularity of ice cream in the nineteenth century, the incidence of foodborne illness attributed to this dessert exploded. Struggling to understand the causes of the mysterious and sometimes lethal ailment called “ice cream poisoning,” Victorian doctors and scientists advanced theories including toxic vanilla, galvanism in ice cream freezers, and extreme indigestion. In the late 1880s Victor C. Vaughan’s argument that ice cream poisoning could be attributed to the ptomaine “tyrotoxicon” received widespread acceptance. To date historians have neglected the role played by the ptomaine theory of food poisoning in shaping the evolution of both scientific thinking and public health in the late nineteenth century. The case of ice cream poisoning illustrates the emergence, impact, and decline of the ptomaine idea.