So because of the reasons that I explained, I wanted to get tissue from human embryos because they presumably lacked interfering viruses and that's what I was looking for in the cancer cells. Well, that was very difficult to do. First of all, you... at that time you didn't have to get permissions, the kinds of permissions that you can today, so it wasn't necessary to get permissions, but it was necessary to arrange things so that you were called on the telephone from a local hospital – notably again the University of Pennsylvania Hospital, which was a huge facility – to be alerted when that tissue becomes available, when an embryo is surgically aborted. The cancer tissue was available almost on a daily basis, so we sent somebody over to the cancer department every day at the end of the day and usually picked up one or two specimens.

But the embryonic tissue was an entirely different story. So in a sense, we had to have people in the paediatric unit pay attention to what we wanted and that was done by convincing the physicians there of why it was important that we get this tissue rather than to incinerate it, which was usually done. And to have cooperation with the nursing staff, etc. And those things were arranged, but as you can well imagine, the telephone would ring saying that embryonic tissue was available at random times, usually five minutes before the end of the working day, which would necessitate calling your family and telling them you won't be home for two more hours because you needed to process the tissue immediately. Of course, that's facetious, but it's usually what happened, Murphy's law at work. So the cultures were set only when... two or three hours after the phone rang which happened sporadically. So what I had done was to initiate culture every time we received an embryo at these random times, set the cultures and did the subcultivation process as they grew out and kept records of the numbers of times that I would do what we call a split or a subcultivation.