What is the relation between things and theories, the material world and its scientific representations? This is a staple philosophical problem that rarely counts as historically legitimate or fruitful. In the following dialogue, the interlocutors do not argue for or against realism. Instead, they explore changing relations between theories and things, between contested objects of knowledge and less contested, more everyday things. Widely seen as the life sciences' first general theory, the cell theory underwent dramatic changes during the nineteenth century. (...) The dialogue establishes that each successive version of the cell theory was formulated -- each identity of the object cell was formed -- around a different material : cork, cartilage, eggs in cleavage, muscle. Such things thus serve as exemplary materials, in ways not described by standard concepts like induction, theory -testing, theory -laden observation, and construction. Still, how can theories and perspective possibly be honed on things if these are apprehended differently by different observers according to their interests, training, culture, or indeed theories? The second part of the dialogue addresses this problem, partly through the verbal and visual schemata that were used by nineteenth-century microscopists and that are comparable to schemata in the visual arts. The third part of the dialogue considers the exemplary materials as a historical sequence, itself needing explanation. Theoretical change devolved partly from wider histories and geographies of the prevalence, availability, or scientific and cultural status of materials such as plants, animals, and muscle. (shrink)