Botulinum toxin
In 1895 (seventy-five years later), Émile van Ermengem, professor of bacteriology and a student of Robert Koch, correctly described "Clostridium botulinum" as the bacterial source of the toxin. Thirty-four attendees at a funeral were poisoned by eating partially salted ham, an extract of which was found to cause botulism-like paralysis in laboratory animals. Van Ermengem isolated and grew the bacterium, and described its toxin, which was later purified by P Tessmer Snipe and Hermann Sommer.
Paul Ehrlich
As a model for experimental therapy Ehrlich used a guinea pig disease trypanosoma and tested out various chemical substances on laboratory animals. The trypanosomes could indeed be successfully killed with the dye trypan red. Beginning in 1906, he intensively investigated atoxyl and had it tested by Robert Koch along with other arsenic compounds during Koch's sleeping sickness expedition of 1906/07. Although the name literally means “nonpoisonous,” atoxyl does cause damage, especially to the optic nerve. Ehrlich elaborated the systematic testing of chemical compounds in the sense of screening as now practiced in the pharmaceutical industry. He discovered that Compound 418 - Arsenophenylglycine - had an impressive therapeutic effect and had it tested in Africa.