Earlier in 1898, Behring and Wernicke had found that immunity to diphtheria could be produced by the injection into animals of diphtheria toxin neutralized by diphtheria antitoxin, as Smith in 1907-09 had suggested that such toxin-antitoxin mixtures might be used to immunize man against this disease. It was Behring, however, who announced, in 1913, his production of a mixture of this kind, and subsequent work which modified and refined the mixture originally produced by Behring resulted in the modern methods of immunization which have largely banished diphtheria.