Emil von Behring and Shibasaburo Kitasato working together in Berlin in 1890 announce the discovery of diphtheria antitoxin serum, the first rational approach to therapy of infectious diseases. They inject a sublethal dose of diphtheria filtrate into animals and produce a serum that is specifically capable of neutralizing the toxin. They then inject the antitoxin serum into an uninfected animal to prevent a subsequent infection. Behring was awarded the Nobel Prize in Medicine or Physiology in 1901.
Behring, E. 1890. Untersuchungen ueber das Zustandekommen der Diphtherie-Immunitat bei Thieren. Dt. Med. Wochenschr. 16: 1145-1148. In Milestones in Microbiology: 1556 to 1940, translated and edited by Thomas D. Brock, ASM Press. 1998, p141 [pdf]
Behring, E. and Kitasato, S. 1890. Ueber das Zustandekommen der Diphtherie-Immunitat und der Tetanus-Immunitat bei thieren. Deutsche medizinsche Wochenschrift 16:1113-1114 In Milestones in Microbiology: 1556 to 1940, translated and edited by Thomas D. Brock, ASM Press. 1998, p138 [pdf]