From Ehrenberg 1870: Microphotographs

Early Micrograph Representation. Ehrenberg sent samples to Gustave Theodor Fritsch (1838-1927), a pioneer of photomicroscopy among many other occupations. Inset image of Fritsch's photomicroscope from "The History of Photomicroscopy" by Normand & Gregor Overney (2010).