Returning now to the cell... cells themselves, in 1962, as I mentioned earlier, I believe, I laid down several hundred ampoules of WI-38 to replace WI-26, which I found was not going to be available for the long period of time I had hoped. I should say at this point, or at least underline, perhaps, one or two things that I mentioned earlier, because they will be of extraordinary... extraordinary importance in about ten years' time, from the time period that I'm presently discussing, so they need to be emphasized.

The first thing is that in our original paper, and as I suggested – I did mention this but didn't emphasise sufficiently, that the difference between the behaviour of normal cells in the laboratory, in a laboratory culture, and cancer cells in a laboratory culture, is that the former are mortal and the latter cancer cells are immortal. And that they have direct in vivo, which means in the body – that is not in a bottle –counterparts. It's suggested, and I argued this case, that our normal body cells are mortal, and that cancer cells that are found to occur in the body are immortal. Although that aspect had already... had been known, cancer tissue had been transferred from laboratory animal to laboratory animal for decades. For example, mouse tumours could be transplanted from mouse to mouse, so over many, many generations, so the immortality of cancer cells was pretty well established in vivo. However, in vitro we only knew of two or three, principally the HeLa cell, so I established this distinction between cancer cells and normal cells.

I mentioned an underline at this point, because it became a critically important part of the cancer research field. Why? Because now you had an opportunity to grow normal cells in culture, expose them to chemicals, transform them into cancer cells, or perhaps expose them to viruses that cause cancer, like the viruses that we call oncogenic viruses, and under these circumstances you can study cancer at the cellular level, which prior to this work was very difficult to do. You didn't need to haul animals in order to make these studies, so the field of cell immortalisation, as it became known over the years, became a very large part of the cancer research effort. It still is today.