DISSOCIATION, a separation or dispersal, the opposite of association but of wider application (see ASSOCIATION) . In chemistry the term is given to chemical reactions in which a substance decomposes into two or more substances, and particu larly to cases in which associated molecules break down into simpler molecules. Thus the reactions and are instances of the first type; of the second. When this breakdown is effected by heating, the process is termed "thermal dissociation." Electrolytic or, as it is termed, ionic dissociation is the separation of a substance in solu tion into ions (see ELECTROLYSIS ; CHEMICAL ACTION : Ionic Theory).
In psychology dissociation is an abnormal condition of the mind wherein the usual connection between various mental elements is lost. Ordinary lapses of memory represent dissociations, in normal minds, between the idea or object which cannot be called to mind and the clue or stimulus idea which formerly sufficed to recall the thing desired. Abrupt changes of mood, or change of interest from one subject to another, in normal people may repre sent emotional dissociation. When large, combined groups of ideas and emotions (complexes) become dissociated from other similar groups, the resulting condition is known as dissociation of personality. Such dissociation is held accountable for many insane conditions. (See DEFENCE MECHANISMS.) In this condition a successful lawyer has been known to draw all his money from the bank, disappear without reason and subsequently open a small shop in a distant city without memory of his former life.