noun
: a largely displaced theory of the chemical basis of immunological phenomena: living organisms are complex aggregations of complex molecules capable of reacting with one another through some of their side chains when these side chains have a definite correspondence in structure exemplified by various outlying cell receptors that can combine with foreign molecules (as of food or toxins), and stimulate the cell to the production of other like receptors some of which may become detached from the cell and function as antibodies