Some of the relationships, such as those between toxins and antitoxins, discovered during the last twenty years have lately been investigated by Arrhenius. It has been found by this observer that many of these processes can be adequately represented by the equations which govern homogeneous mass reactions; for instance, the rates of the disappearance of diphtheria antitoxin and of typhoid agglutinin from the circulation are described at least empirically by such a formula (Diagram I.)