A Brief History of Xenopus

This essay will appear in our forthcoming book, “Making the Modern Laboratory,” to be published later this year.

By Matt Lubin

Until the 20th century, there was no easy way to detect a pregnancy. One could wait for two missed menstrual cycles, watch for the first signs of a baby bump, or listen closely for a fetal heartbeat, but none of these methods work until several months into gestation. Ancient and medieval sources describe a variety of possible tests to determine whether a person was pregnant, but none were remotely reliable by modern standards.1

In the 19th and 20th centuries, researchers began looking for a solution in the emerging science of endocrinology, the systematic study of hormones. It was during this era that doctors and biologists began to shift from studying anatomy (observing the mechanics of visible organs) to exploring the invisible potency of “internal secretions” and “juices” that directed bodily phenomena. Early experiments by endocrinologists were crude, however, usually involving the injection of fluids from one animal (or human) into another and seeing what happened.

One pioneering endocrinologist who predicted the existence of hormone chemicals was Charles-Édouard Brown-Séquard. In 1889, he shared results from a “study” in which he injected himself with an elixir of “the three following parts: first, blood of the testicular veins; secondly, semen; and thirdly, juice extracted from a testicle, crushed immediately after it has been taken from dog or a guinea-pig.” Brown-Séquard found that these testes-semen injections restored to him all the vigor of his youth, though few others have been able to reproduce his results.2

In this spirit, two doctors working in Berlin, Selmar Aschheim and Bernhard Zondek,3 discovered an early pregnancy test in 1928 by injecting patients’ urine into laboratory mice. A few days after the injections, the mouse would be killed and dissected so that its ovaries could be examined; if the patient who provided the urine sample was pregnant, the mouse would develop “ovarian blood spots.”

In the U.S., Maurice Friedman adapted this approach for rabbits because a single rabbit could handle a larger volume of urine, their ovulation patterns are a bit more reliable, and clinical centers generally found them easier to house. His “rabbit test,” released in 1931, became the American standard for several years. Yet both the mouse and rabbit tests had significant drawbacks: they required waiting several days for results, and