A painting showing inoculated horses being bled for their serum containing diphtheria antitoxin (1900). Diphtheria is an acute infectious disease caused by the bacterium Corynebacterium diptheriae, which produces toxins which damage nerves and heart muscle. In 1890 Emil von Behring discovered that horses inoculated with the bacteria produce antitoxin antibodies. Administration of the horse blood serum to people who have contracted diphtheria will neutralise the bacterial toxins, which are inactivated by the horse's antibodies. This procedure is now less common since most children are immunised against the disease.