It's necessary to jump back to the cell culture story because by this time I was also becoming inundated with dozens of requests for my human diploid cell strains by virologists, really all over the world. And also I now realised – and I'll return to this later in more detail – that these cells could in fact replace the then used cells, used for the experiments and production by Sabin Salk and Koprowski for the production of the polio vaccine because the cells that were used by these three folks at that time were primary monkey kidney cells. By that I mean cells from a monkey's kidney isolated by trypsin from the kidney tissue itself, put into culture and never... not subcultivated and that's a key concept. Once they're passaged, I call it a strain. If they're not passaged... if they're the original cells from the tissue, it's called a primary cell population and that will become key later.

What was developing at this time – so many things happening within a framework of 18 months – is that people were beginning to realise that those primary monkey kidney cells contained unwanted viruses. They contained indigenous viruses like the ones we knew could be found in some human adult tissue. And many of those viruses had behaviours that were unknown and if they contaminated the vaccines that these men were making, it would be... could be a disaster. By this time I had proven that my cells were absolutely clean. They had no indigenous viruses whatsoever by every test known.

I mention all of this only to try to give you some impression of the ferment in my lab learning more about these cells, teaching people now coming to my laboratory for a week or two to learn how to handle the cells, distributing them, trying to make a vaccine in them and simultaneously trying to work with this mycoplasma story with Bob Chanock. It was impossible for me to pursue... I had to make a choice. Do I work with the cells or do I work with the mycoplasmas? I chose the former and by chance, another chance observation, the Journal of Bacteriology arrived on my desk about this time and described the very procedure that we needed. It was described in a letter to the editor, so it was no more than a page long article. I do not recall the authors. And they described a very simple method of removing the colonies from an ager plate – mycoplasma colonies – and having them now resting on a glass slide that you can put under a microscope. Well, that was perfect because now if we could do that, and this described how to do it, we could now stain the colonies on a glass slide and see if they fluoresced or not by the technique I just described.