John Rock’s patients. To ‘harvest’ elusive embryos, Rock recruited married women under 45 with at least two children who were scheduled for hysterectomy. They were asked to keep diaries of their periods, body temperature and sexual intercourse. Rock’s assistant Miriam Menkin admitted that she hinted to the patients that it would be helpful if they had sex before the operation, which was scheduled to follow ovulation closely. Data from the women’s diaries were combined with the morphology of the embryo and changes in the uterine lining specific to each day of the menstrual cycle to date specimens unusually precisely. At the time, no one involved regarded the procedure as an artificial abortion; once it was seen in this way, the work became impossible to repeat.

The Boston egg hunt

In the late 1930s the Carnegie Department set out to recover embryos younger than 14 days from gynæcological operations.

Before a woman missed her period and the new hormonal pregnancy tests could turn positive, embryos remained undetectable. So in 1938, John Rock, a Boston gynæcologist, human fertility researcher and practising Catholic, teamed up with a pathologist with Carnegie research experience on fertilization in monkeys, Arthur T. Hertig, and technician Miriam Menkin. She became Rock’s long-term collaborator as they looked for the earliest products of conception in surgically removed Fallopian tubes and uteri.

Yet spotting such an early human embryo was very hard, especially since no one had seen one before. Hertig reported that ‘we looked at an enormous amount of eggs that weren’t eggs, just cellular debris, because … the art of actually recognizing a human egg hadn’t been mastered’. In late 1938, he described the first complete fertilized egg he saw under his microscope as a ‘glistening bead, like a pearl of tapioca’. The 12-day ‘Harvard egg’ was examined, measured and then transported to Baltimore. The 34 fertilized eggs from 211 unknowingly pregnant women, collected by Hertig and Rock over the course of 14 years, came to represent the first 17 days of life.

The Free Hospital for Women, associated with the Harvard Medical School, c.1950


Drawing of the Harvard egg, 1941