\Side"-chain` the`o*ry\ (Physiol. Chem.)
A theory proposed by Ehrlich as a chemical explanation of
immunity phenomena. In brief outline it is as follows: Animal
cells and bacteria are complex aggregations of molecules,
which are themselves complex. Complex molecules react with
one another through certain of their side chains, but only
when these side chains have a definite correspondence in
structure (this account for the specific action of
antitoxins).