Pfeiffer, Richard Friedrich Johannes (1858–1945)

German bacteriologist who determined how to distinguish the organism that causes cholera and was the first to observe the body's immune response to an invading microbe.

Pfeiffer found that if a guinea pig is immunized against cholera, cholera vibrio (cholera bacteria) can be injected into its peritoneal (abdominal) cavity without any ill effects. He then withdrew some of the peritoneal fluid and examined the cholera germs microscopically. He observed that they swelled up and disintegrated. They had been lysed (destroyed) by some substance in the peritoneal fluid. Other organisms that resembled the cholera vibrio were not affected in this manner; the reaction was very specific. Pfeiffer managed to produce the reaction in vitro (in an artificial environment). He then demonstrated that the cholera vibrae were not lysed if the peritoneal fluid was heated to 60°C.

Pfeiffer was educated in Berlin as a military surgeon. He worked with the great bacteriologist Robert Koch at the Institute for Hygiene in Berlin and then became the professor of hygiene at Koenigsberg. In 1909, he was elected professor of hygiene at Breslau.