"...1916, Dr. Papanicolaou was studying sex chromosomes in guinea pigs, for which he had to obtain eggs in the early stages of mitosis. But it was impossible to determine where the guinea pig was in its estrous cycle without killing it. One night it occurred to him that guinea pigs, like humans, must have a menstrual cycle, even though no bleeding had been observed. If so, one should be able to obtain the necessary information from the vaginal secretions.
The next morning he took what was probably the first Pap smear — from a guinea pig. The specimen revealed “an impressive wealth of diverse cells” under the microscope. The method of studying the “shed” cells from the vagina became a standard for testing the effects of hormones and drugs on reproductive organs. Soon Dr. Papanicolaou, in collaboration with Herbert Traut, MD, extended this method for studying vaginal cytology to human beings."
So if it weren't for guinea pigs, we might not have the pap smear.
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