1834 The natural history of animalcules : containing descriptions of all the known species of Infusoria : with instructions for procuring and viewing them London, Whittaker and Co.
In his Vermium Terrestrium et Fluviatilium, seu Animalium Infusoriorum, Helminthecorum, et Testaceorum non Marinorum, succincta Historia (2 vols. 4 to, Copenhagen and Leipzig, 1773–74), he arranged the Infusoria for the first time into genera and species.
He was also a diligent and skillful observer, and busied himself not only with astronomical subjects, such as the double stars, the satellites of Jupiter and the measurement of the polar and equatorial diameters of the sun, but also with biological studies of the circulation of the sap in plants, the fructification of plants, infusoria etc.