Richard Pfeiffer, working with Robert Koch in Berlin, intellectually and experimentally conceived the concept of endotoxin as a heat-stable bacterial poison responsible for the pathophysiological consequences of certain infectious diseases. Pfeiffer's definition of endotoxin included the inability to evoke neutralizing antibodies against this bacterial toxin. Alexandre Besredka, Ilya (Elie) Metchnikoff's successor at the Institut Pasteur in Paris, was the first to demonstrate that, in fact, antibodies could be engendered which were capable of suppressing the poisonous effects of endotoxin. Endotoxin and anti-endotoxin antibodies have since then fascinated researchers of many disciplines and continue to do so, particularly in the fields of diagnosis, prevention, and therapy of severe Gram-negative infections.