The replacement of one thing by another. a. In chemistry, the replacing of one or more elements or radicles in a compound by other elements or radicles. is the principal method em. ployed in examining the chemic structure of organic bodies. It is also called metalepsy. b. In medicine, the action of the unaffected hemisphere of the brain in taking up the function of the diseased opposite hemisphere. In general, the vicarious action of organs. In pharmacy, the supplying of another drug or compound instead of the one ordered or called for.

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Definition of  SUBSTITUTION