Microbes before microbiology: Christian Gottfried Ehrenberg and Berlin's infusoria

Naturalist Christian Gottfried Ehrenberg pioneered research on living and fossil infusoria (including protists and bacteria) since the 1830s by collecting samples from all over the world, thus describing numerous microbes and discussing their effects for the planet and for humankind. This article introduces Ehrenberg as a natural historian of microbes and situates his work in the nineteenth century life sciences with respect to debates about cell theory, evolution, and concepts of disease. I argue that in spite of occurring before these major conceptual innovations of the life sciences, Ehrenberg's work on the diversity of microbes found in earth or air is more exciting than historiography has made it appear so far, especially in light of today's ecological microbiology.