In the 1930s, Maurice H. Friedmann and Maxwell E. Lapham developed a test using rabbits that gave a rapid reaction to the pregnancy hormone.
Under anaesthetic, ovaries are obtained from female rabbits that are sexually mature but not pregnant. The ovaries are long and round and yellowish-white in colour and are smooth with individual glassy follicles on the top surface. Still under anaesthetic, urine from a woman who suspects she might be pregnant is injected into a vein in the animal’s ear.
Forty-eight hours later the abdomen is re-opened and the ova examined carefully: bleeding follicles or yellow bodies (Corpus luteum) that bleed when touched indicate a pregnancy.
The 'rabbit test' got a literary mention in the Michael Crichton book 'A Case of Need'. "He wouldn't have aborted her without doing a bunny test first, and such a test would have been negative."
From Laboratory Diagnostics by Dr. Th. Leipert
Further excerpts from Crichton’s novel 'A Case of Need' can be found here: http://en.muvs.org/topic/michael-crichton-die-intrige-1968-en/