What kind of tools might a researcher create to identify a new scientific fact? What is there in common between the construction of the fact and its reception? How do the contents of a laboratory notebook interact with scientific correspondence networks and related publications? In this French-language book, Ratcliff explores these questions as he reconstructs both the discovery of the division of Infusoria (fresh- and pond-water unicellular organisms) by Geneva scholar Horace-Bénédict de Saussure (1740–99) and its reception by the late eighteenth-century scientific community. Combining micro-historical and epistemological analysis in order to investigate the double path of the researcher and his object, Ratcliff proposes a new understanding of the relationships between construction, discovery, and reception.