Some chemical substances can so stimulate the motor areas of the central nervous system that a person's muscles begin to powerfully convulse (begin uncontrollable violent contractions). Some natural and manmade chemicals are capable of producing such reactions. For example, tetanospasmin, a chemical produced by the bacteria Clostridium tetani, is such a natural agent. Strychnine, a poison, once was used as a respiratory stimulant; however, its medicinal use has been stopped because of its toxicity.
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