Ferdinand J. Cohn contributes to the founding of the science of bacteriology. He publishes an early classification of bacteria, using the genus name Bacillus for the first time.

Robert Koch publishes a paper on his work with anthrax, pointing explicitly to a bacterium as the cause of this disease. This validates the germ theory of disease. His work on anthrax was presented and his papers on the subject were published under the auspices of Ferdinand Cohn.

Joseph Lister publishes his study of lactic fermentation of milk, demonstrating the specific cause of milk souring. His research is conducted using the first method developed for isolating a pure culture of a bacterium, which he names Bacterium lactis.

Louis Pasteur develops a method of attenuating a virulent pathogen, the agent of chicken cholera, so it would immunize and not cause disease. This is the conceptual breakthrough for establishing protection against disease by the inoculation of a weakened strain of the causative agent. Pasteur uses the word ”attenuated” to mean weakened. As Pasteur acknowledged, the concept came from Edward Jenner’s earlier success at smallpox vaccination.

Robert Koch struggles with the disadvantages of using liquid media for certain experiments. He seeks out alternatives, and first uses an aseptically cut slice of a potato as a solid culture medium. He also turns to gelatin, which is added to culture media; the resulting mixture is poured onto flat glass plates and allowed to gel. The plate technique is used to isolate pure cultures of bacteria from colonies growing on the surface of the plate.

Ilya Ilich Metchnikoff demonstrates that certain body cells move to damaged areas of the body where they consume bacteria and other foreign particles. He calls the process phagocytosis. He proposes a theory of cellular immunity. With Paul Ehrlich, Metchnikoff is awarded the Nobel Prize in Medicine or Physiology in 1908.

Robert Koch puts forth a set of postulates, or standards of proof, involving the tubercle bacillus. Koch's postulates are published in The Etiology of Tuberculosis, in which he demonstrated three major facts: 1) the presence of the tubercule bacillus (as proved by staining) in tubercular lesions of various organs of humans and animals, 2) the cultivation of the organisms in pure culture on blood serum, and 3) the production of tuberculosis at will by its inoculation into guinea pigs. Koch was awarded the Nobel Prize in Medicine or Physiology in 1905.

Louis Pasteur oversees injections of the child Joseph Meister with “aged” spinal cord allegedly infected with rabies virus. Pasteur uses the term “virus” meaning poison, but has no idea of the nature of the causitive organism. Although the treatment is successful, the experiment itself is an ethical violation of research standards. Pasteur knew he was giving the child successively more dangerous portions.

Martinus Beijerinck uses enrichment culture, minus nitrogenous compounds, to obtain a pure culture of the root nodule bacterium Rhizobium, demonstrating that enrichment culture creates the conditions for optimal growth of a desired bacterium.