Diphtheria antitoxin contains polyclonal antibodies against the diphtheria toxin. Behring had been investigating antibacterial agents and discovered a diphtheria antitoxin. The only treatment available in 1925 was diphtheria antitoxin serum. His bioassay on diphtheria antitoxin was the first bioassay to receive recognition. In 1897, Paul Ehrlich developed a standardized unit of measure for diphtheria antitoxin. Botulism is generally treated with botulism antitoxin and supportive care. In 1901, 10 of 11 inoculated St. Louis children died from contaminated diphtheria antitoxin. The horse from which the antitoxin was derived died of tetanus. This less immunogenic antitoxin is effective against all known strains of botulism where not contraindicated. The administration of horse antitoxin remains the only specific pharmacologic treatment available for botulism. These toxin-producing strains cause scarlet fever in people who do not already have antitoxin antibodies. Toxin-antitoxin systems are typically classified according to how the antitoxin neutralises the toxin. Prophylactic antihistamines or corticosteroids may be used concomitant with the antitoxin. Another example application involves both the CcdB toxin and CcdA antitoxin. If infection occurs, treatment is with antibiotics and possibly antitoxin.