If you ever get the question "which common amphibian was used as a pregnancy test in the 1930s?" at pub trivia, you're going to want to kiss me after reading this. The answer, rather extraordinarily, is the South African clawed frog. A lady frog, to be specific. In the 1930s, a British scientist named Lancelot Hogben made a discovery that would change the course of reproductive history. The experimental zoologist found that injecting the urine of a pregnant human into the frog's hind leg worked as an effective pregnancy test. If the woman who supplied the urine was pregnant, the frog would ovulate and produce eggs. It was the presence of a human hormone we now call human chorionic gonadotropin (hCG) that triggered the release of eggs, usually within a 12-hour period.

The frog pregnancy test, named the Hogben Test quickly became popular. By the 1940s in Britain, there were three specialized centers covered by the National Health Service (NHS) where doctors would send urine samples to get tested. Women could not send their samples directly; in fact, if they tried to, they would not be tested. These early centers were reserved for medical emergencies, like distinguishing between pregnancy and the growth of a tumor. They were by no means an easily available pregnancy test. The Hogben Test was, for quite some time, the only humane way of using an animal to detect whether an adult lady woman was "in the family way," in the common parlance of the day.

Read more: The Controversial Birth Control That Destroys Your Body

Such a frog is on display at the Wellcome Collection in London right now: It is mounted in a glass case as part of the exhibition Making Nature, which explores the ways humans have come to understand and interact with the natural world. That particular frog belongs to Richard "Rich" Pell, a curator from the Center of PostNatural History in Pittsburgh, Pennsylvania. To find out more about how this frog plays into this curious piece of birth control history, I spoke to Rich about his specimen.

As it turns out, Pell has three African clawed frogs: the one I've seen in the exhibition, one at his own museum and one in his freezer at home next to his wife's placenta (don't ask). The one currently residing in the Wellcome Collection is actually the least interesting: he found it while rummaging around in the basement of a nearby museum. The second was a gift from an excitable man who donated several reptiles and amphibians to the PostNatural Museum. The third—now frozen—frog was bred specifically to do a live test at a university lecture at the school where Pell teaches, two years ago.

A South African clawed frog from Richard Pell's collection. Photo courtesy of Richard Pell

"One of the things I do for the museum is study the origins of organisms that get used in the lab, so the white mouse, the white rat, the zebra fish and the fruit fly," Pell says. "And then there's this frog: the South African clawed frog, Xenopus laevis. They use it all over the world for research in biology and genetics these days. So when I looked into why people use this particular frog, I found out that it had a really specific origin story. The first group of those frogs, 18 of them, were brought over from England to the US for the first time by the organization that would eventually become Planned Parenthood.

"At the time, they were the American Birth Control League, and the year was 1937," he continues. "It was a big deal because this was the 1930s—in the US, birth control was illegal and basic information about human reproduction was illegal. So this whole operation was pretty radical for the people involved. They brought them over by hand in a cooler, as I understand, and started a lab that could do these kinds of pregnancy tests in the US."

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This led to an almost instantaneous industry of frog pregnancy tests in the US. Labs like these proliferated, as did the frogs, with thousands imported from South Africa for the express purpose of pregnancy testing. "It got very big very quickly," says Pell. "It was a real revolution. It was the first wave of a reproductive revolution, it's what preceded the legalization of birth control. It was the first meaningful way that women had to take control. And it was maybe another 10 or 15 years before there was a chemical litmus test that worked in the same way. It really did serve to jumpstart that sexual revolution and helped to empower the group that becomes Planned Parenthood in the act of getting birth control legalized."