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A poisonous substance, usually of microbial origin, that stimulates the production of antitoxins in an animal body. Many bacterial diseases are due to the release of bacterial toxins. These may be endotoxins, which are formed within the bacterium and released on the death and disintegration of the bacterial cell, or exotoxins, which are secreted through the bacterial cell wall. The exotoxins, many of which are highly active enzymes, generally have more severe effects. Several fungi, e.g. death cap (Amanita phalloides) and ergot (Claviceps purpurea), also produce toxins. Aflatoxins, produced by the mould fungus Aspergillus flavus, can cause severe liver damage. Higher plant toxins are less common, an example being ricin, an albumin in castor oil (Ricinus communis) seeds, that causes agglutination of red blood cells.
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