Jenner and Pasteur developed vaccines that enabled the body to respond to invading foreign microbes.

Koch developed mechanisms for the discovery of the etiologic agents of disease.

von Behring and Kitasato, working in Koch's Lab, discovered that immunoglobulins in the bloodstreamcould fight infection.  Their work would begin the studies of serology and immunology.

Erlich (salvarsin), Fleming (penicillin) and Domagk (sulfa drugs) would pioneer the study of chemotherapy.