In 1904 he delivered at the university of California a course of lectures, the object of which was to illustrate the application of the methods of physical chemistry to the study of the theory of toxins and antitoxins, and which were published in 1907 under the title Immunochemistry.
Von Behring completed the sphere of the new study by his discovery of the antitoxins of diphtheria and tetanus.
Of such probably are the toxins and antitoxins of certain infections, which, anchoring themselves not by any means indiscriminately, but to particular and concerted molecules, by such anchorage antagonize them or turn them to favourable or unfavourable issues.
In the mutual behaviour of such cells, toxins, and antitoxins, and again of microbes themselves, we may demonstrate even on the field of the microscope some of the modes of such actions, which seem to partake in great measure at any rate of a chemical quality (agglutinins, coagulins, chemotaxis).
The effect of the abnormal conditions is probably to stop the production of, or weaken or destroy the protective enzymes or antitoxins, the presence of which normally confers immunity on the leaf.