In 1888 Emile Roux and Alexandre Yersin showed that the clinical effects of diphtheria were caused by diphtheria toxin and, following the 1890 discovery of an antitoxin-based immunity to diphtheria and tetanus by Emil Adolf von Behring and Kitasato Shibasaburō, antitoxin became the first major success of modern therapeutic immunology. Shibasaburo and von Behring immunized guinea pigs with the blood products from animals that had recovered from diphtheria and realized that the same process of heat treating blood products of other animals could treat humans with diphtheria. By 1896, the introduction of diphtheria antitoxin was hailed as "the most important advance of the Century in the medical treatment of acute infective disease".