rabbit test / the rabbit died

The term rabbit test dates to 1949 and is a reference to an early form or pregnancy test. In the 1920s, researchers discovered a hormone dubbed human chorionic gonadotropin or HCG found in the urine of pregnant women. Unable to test for this hormone directly, they discovered in 1927 that if a female rabbit was injected with urine containing HCG (don’t ask me who first thought of doing this, I don’t think I want to know), the rabbit’s ovaries would display distinct changes after a few days. Hence, the term rabbit test was born, first appearing in the index of De Lee’s Safeguarding Motherhood. Speert’s 1958 Obstetric and Gynecologic Milestones has this:

The urine of pregnant women contains a gonadotrophic substance simulating the secretion of the anterior pituitary in its effect on the mouse ovary. Applying this observation to the rabbit, Friedman proceeded to develop the pregnancy test known by his name, popularly as the “rabbit test.”

A common misconception is that that the rabbit died if the woman was pregnant. Actually, the rabbit always died as the laboratory had to kill the animal to examine the ovaries (later on techniques were developed to spare the life of the rabbit—after which the rabbit never died). But because of this misconception the phrase the rabbit died entered the vocabulary as a euphemism for a positive pregnancy test.

Modern pregnancy tests still operate on the same principle, testing for HCG. But the use of a rabbit is no longer required.

(Source: Oxford English Dictionary, 2nd Edition)

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