Diphtheria Antitoxin - 1895
Diphtheria is a killer by the toxins it excretes, which can cause necrosis, myocarditis, and, most dangerously, the putrid-smelling pseudo-membrane that can line the pharynx and trachea, preventing breathing.
Antitoxins were the first solution to these toxins. Antibodies against the toxin were taken from the serum of large animals (horses) who were inoculated with the toxin produced by the C. diphtheriae bacteria. The amount of toxin was small enough that it only produced an immune reaction in the animal, and did not poison them.
When someone contracted diphtheria, the antitoxin could be injected, and this inactivated the circulating toxin created by the bacteria. While it did not kill the bacteria itself, the immune system was capable of doing that on its own when it wasn’t busy being dissolved and ripped apart by the toxins. Unfortunately, the antitoxin could not inactivate toxins created by bacteria that were already bound to tissues, so the earlier it was administered, the better.
Combined with the refinement of the tracheotomy (so that patients could breathe, even with a pseudo-membrane covering their airway), the antitoxin dropped the mortality rate of diphtheria from 40-45% down to around 12-15%.
Image: Production of antitoxin by inoculation of horses. One of the first bottles of antitoxin produced at the Hygienic Lab, later known as the National Institutes of Health.