Hogben never alluded to this application in his early reports, but it wasnвЂ™t long before he was working towards it. If those same hormones could trigger egg-laying in Xenopus, perhaps the frog could act as a living pregnancy test. At the time, scientists knew that the urine of pregnant women contained hormones that were made in the pituitary and that affected the development of ovaries. This accidental finding was a fortuitous one. In response, the frog started laying eggs. In 1930, Hogben injected Xenopus with extracts from an oxвЂ™s pituitary gland-a pea-sized hormone factory at the base of the brain. One of them- Xenopus-was so abundant and easy to work with that Hogben spent much of his time with the creature, and even named his house after it. In his early career, he studied hormones by injecting them into frogs, and when he moved to South Africa in 1927, he continued those experiments with the local amphibians. Hogben was a talented but irascible zoologist with strident left-wing politics and penchant for burning bridges. That unbroken streak changed in the 1930s, thanks to a British scientist with the fantastic name of Lancelot Hogben.

The African clawed frog, Xenopus laevis, is a palm-sized, greenish-gray animal that hails from the ponds and rivers of sub-Saharan Africa, where it lived for millions of years without anyone injecting it with urine.

Pregnant frog dissection