If a black mamba bites you, the treatment that saves your life is made much as it was more than a century ago: by injecting diluted venom into horses, sheep, or even camels and harvesting the antibodies from their blood. This episode explains why. Venom works too fast for the body to build its own defense, so a large animal serves as a surrogate immune system. The plasma is purified and often freeze dried into a powder that keeps for up to five years without refrigeration. The price is risk, since animal proteins can trigger serum sickness or anaphylaxis in the patient.

The history runs from Felice Fontana’s 1767 observation that venomous snakes survive their own bites, through Henry Sewall’s pigeons in 1887, to Albert Calmette’s horse serum against Indian cobra venom in 1894 and Vital Brazil’s multi-species antivenoms in 1901. The present is less heroic. Production is costly, the people bitten most are rural workers who cannot pay, and makers walk away. The episode closes with possible replacements, from an opossum protein to synthetic antibodies and one man’s unusual blood.

• Doctors give antivenom even to patients allergic to horses, because anaphylaxis can be managed in intensive care and paralysis from venom cannot be undone.
• Sewall raised pigeons’ tolerance until they survived seven times the normal lethal dose of rattlesnake venom.
• The United States ran out of in-date coral snake antivenom in 2009 after the maker judged a few dozen bites a year unprofitable.
• Without antivenom, hospitals may use neostigmine, which floods nerve junctions with the body’s own signal to keep paralyzed muscles working.
• Antibodies from a man who let snakes bite him for years, combined with the enzyme inhibitor varespladib, protected mice from lethal venom of several species.