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Chapter 47 : Ferdinand Cohn, Neglected Visionary
Ferdinand Cohn’s principal achievement, recorded in Untersuchungen über Bacterien in 1872, was to show that bacteria could be categorized, like plants and animals, into genera and species. He demonstrated that bacilli, for example, did not transmute capriciously into cocci, nor vice versa. About a quarter of the Escherichia coli genome, for example, seems to have been acquired from other species. Again, this need not pose insuperable problems for systematists trying to fathom the relationships between different organisms, nor does it compromise the identification of clinical isolates in hospital laboratories. Just as Cohn, ahead of his time, grasped that morphology should be combined with physiology in classifying organisms, so he would have welcomed the new computational methods that are beginning to resolve the taxonomic dilemmas posed by gene swapping. Together with Louis Pasteur, for example, Cohn denounced the idea of spontaneous generation, but he went further, becoming the first person to demonstrate that organisms such as Bacillus subtilis can form spores that are resistant to heat and other physical agents. He showed that many bacteria can be killed by being boiled but that spores are more resistant than vegetative forms. This was a crucial discovery in invalidating the work of Henry Bastian.