Early editions of the index were a tabbed notebook. “I still have some of the original versions of it,” Boyer says. “You would go through, laboriously, by hand, turning the pages, and it would say ‘see page 27,’ like one of those find-your-own-ending books, and then you would put in a phone call, because the last section in the Antivenom Index was the home phone numbers of zookeepers.”

In 2006, Boyer and Steven Seifert, then a medical toxicologist at the University of Nebraska, partnered to bring the index online, where it remains today. Now, nearly 90 zoological organizations list their wares.

When Chris Gifford was bitten by his deadly green mamba, he was lucky to receive antivenom from South Carolina’s Riverbanks Zoo.

Courtesy of Chris Gifford

Gifford, the North Carolina man, had been comparatively lucky, as only one of his mamba’s fangs had pierced his skin. By the time he reached a nearby hospital, Gifford’s hand was swelling and creeping paralysis was causing his eyelids to droop. The Antivenom Index was activated, and South Carolina’s Riverbanks Zoo, about 200 miles to the southwest, had the antivenom he needed. Just 30 minutes after the mamba’s bite, Gifford was struggling to breathe as the paralysis started to affect his diaphragm.

“It feels like you’re drowning,” he says.

Keepers at the Riverbanks Zoo packed 10 vials of antivenom on ice and sent them on a helicopter. Just as Gifford’s timer hit the six-hour mark, the hospital began administering the first of the vials. “Almost immediately, I could feel myself breathing,” Gifford says. He left the hospital some two days later.

If you’re bitten by a venomous snake in the northeastern United States, odds are good that you’ll be treated with vials of antivenom nestled in a refrigerator in the back room of the Bronx Zoo’s reptile house. The zoo collaborates with the nearby Jacobi Medical Center, whose dedicated snakebite response team makes it a rarity among US hospitals.

Inside the refrigerator are boxes, bins, and bags of the delicate glass vials that are often the difference between life and death. Shelves are lined with jars full of antivenom for Indian species and the North American coral snake, and lavender cartons with images of a poised king cobra. In all, the Bronx Zoo stocks 25 different antivenom varieties, many of which are polyvalent, meaning applicable to multiple species.