If you've strolled in New York's Central Park, you may have noticed the statue honoring Balto, the Siberian husky who braved the elements to bring lifesaving medicine to the inhabitants of Nome, Alaska, during a 1925 diphtheria epidemic. But what Balto risked his hide to haul wasn't antibiotics. Instead, the trusty canine brought with him a load of serum, a product made from the blood of animals such as horses, and containing antibodies that they'd developed from being exposed to the disease. The idea was that when the serum was injected into humans' bodies, it fought the bacterial invaders again [source: Koerth-Baker].
Serum therapy was invented in the 1890s, and one of its discoverers, Emil von Behring, was awarded a Nobel Prize for his work [source: Nobelprize.org]
Serum therapy largely was supplanted by antibiotics — diphtheria, for example, is now treated with penicillin and erythromycin [source: MedLine Plus]. But the concept hasn't completely gone away. When the Ebola epidemic raged through West Africa in 2014, for example, the World Health Organization considered giving victims a serum made from the blood of people who had recovered from the infection [source: Kupterschmidt].