Cohn, Ferdinand Julius (1828–1898)

German botanist and bacteriologist who showed that bacteria are not able to generate spontaneously but can develop from spores, and developed a system of classification for bacteria. Working primarily on algae, he also demonstrated that some primordial plant cells lack cellulose cell walls.

In 1872, he developed a system for the classification of bacteria based upon their morphology, grouping them into four classes: Sphaerobacteria, Microbacteria, Desmobacteria, and Spirobacteria. In 1876, he demonstrated that Bacillus subtilis had thermoresistant (heat-resistant) spores and was not able to generate spontaneously.

Cohn was born in Breslau in Lower Silesia and is reported to have learnt to read by the age of two and to have known the basics of natural history by three. However, at the age of ten his hearing became impaired, slowing his amazing academic progress. In 1842, he went to the University of Breslau to study philosophy and soon became interested in botany, but because he was a Jew he was unable to obtain a degree. This prompted him to transfer to the University of Berlin, where he obtained a doctorate in botany 1847, at the age of nineteen. In 1849, he returned to Breslau, where he was made extraordinary professor of botany 1859 and ordinary professor of botany 1872.