The term endotoxin was coined by Richard Friedrich Johannes Pfeiffer, who distinguished between exotoxin, which he classified as a toxin that is released by bacteria into the environment, and endotoxin, which he considered to be a toxin kept "within" the bacterial cell and to be released only after destruction of the bacterial cell wall. Today, the term 'endotoxin' is used synonymously with the term lipopolysaccharide, which is a major constituent of the outer cell membrane of Gram-negative bacteria.
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