"When Hayflick opened up that icy package from Sweden in 1962, he was working at the vanguard of virus research in the United States. At the time, the Wistar Institute was led by Hilary Koprowski, a polio-vaccine pioneer who hired Hayflick to run the centre’s cell-culture laboratory and supply cells to researchers. But Hayflick also began investigating whether some human cancers might be caused by viruses. To do so, he needed a resource that did not yet exist: verifiably normal human cells that could be reliably grown in the lab. Fetal cells, he thought, were an ideal candidate, because they were less likely to have been exposed to viruses than adult cells. Although abortions were technically illegal in Pennsylvania at the time, they were still performed when doctors said they were medically necessary. Hayflick says he was able to obtain fetuses straight from the operating room of the University of Pennsylvania Hospital across the street from Wistar. Unless the tissue was put to some use, he reasoned, “it was definitely going to end up in an incinerator”. The University of Pennsylvania says that it is unable to find records to confirm the source of fetal tissues used by Hayflick. Hayflick developed 25 different fetal-cell strains, numbered WI-1 to WI-25. But several months into the project, he began to notice something strange. Scientific orthodoxy held that cells in culture, properly treated, would replicate forever. But his oldest cell strains were beginning to replicate more slowly. Eventually, they stopped dividing altogether."