In this work Ehrenberg first published his classification of infusioria, including the naming of bacteria for the first time. The work published two papers based on his expeditions. The first, read on January 10, 1828, was "Die geographische Verbreitung der Infusionsthierschen in Nord-Afrika und West-Asien, bebachtet auf Hemprich und Enrenbergs Reisen". This was the work in which Ehrenberg first published his classification of infusoria, and named bacteria. In it he set out his findings from travels through north Africa and Arabia in 1820-1825, during which he accumulated some 34,000 zoological and 46,000 botanical specimens. Considering the enormous amount of material accumulated, it must have taken Ehrenberg a few years to organize and summarize some of the findings.

Ehrenberg's second paper, read on March 4 and 18, 1830, was "Beiträge zur Kenntniss der Organisation der Infusorien und ihrer geographischen Verbreitung, besonders in Sibirien." In this lectures he recounted findings during his travels through Russia, which were patronized by Alexander von Humboldt, and financed by Czar Nicholas I.

Digital facsimile from Biodiversity Heritage Library at this link.

In this monumental work in folio format Ehrenberg extended Otto Friedrich Müller’s bacteriological classification. Like Müller, he made no distinction between protozoa and bacteria, classing them both as infusoria. His classification included Bacterium, which he described and named in 1828, and published in 1830, Vibrio, Spirillum and Spirochaeta. The fine hand-colored plates in this book were drawn by Ehrenberg himself. Includes (p. 80) first description of B. subtilis.

Ehrenberg's book was translated into French with the atlas in reduced  8vo format and condensed to 8 uncolored plates, as Traité pratique du microscope, et de son emploi dans l'étude des corps organisés par le docteur L. Mandl; suivi de Recherches sur l'organisation des animaux infusoires par D.-C.-G. Ehrenberg. Accompagné de quatorze planches. (Paris: J.-B. Baillière, 1839). Digital facsimile of the 1839 translation from Biodiversity Heritage Library at this link.