This article proposes to analyze the idea of organism and other closely related ideas (function, differentiation, etc.) using a combination of semantic fields analysis from conceptual history and the notion of boundary objects from the sociology of scientific knowledge. By tackling a wide range of source material, the article charts the nomadic existence of organism and opens up new vistas for an integrated history of the natural and human sciences. First, the boundaries are less clear-cut between disciplines like biology and sociology than previously believed. Second, a long and transdisciplinary tradition of talking about organismic and societal systems in highly functionalist terms comes into view. Third, the approach shows that conceptions of a world society in Niklas Luhmann's variant are not semantic innovations of the late twentieth century. Rather, their history can be traced back to organicist sociology and its forgotten pioneers, especially Albert Schäffle or Guillaume de Greef, during the last decades of the nineteenth century.