Returning to the events in the laboratory in the early 1960s, I should describe the events that occurred after the freezer failure in which I lost all 25 of the original human... normal human strains that were described. And so, I invented a replacement called WI-26, and because all of the previous strains seemed to have the same properties, that we were interested in at least, one strain was sufficient to develop. And my goal was to lay down in our liquid nitrogen freezer, I think we had by this time, which was more... which was safer and less likely to... to force loss of cell ampoules we develop another strain.

Because the... there was WI-25, the obvious name for the one that I was going to make was WI-26. And that one was a male cell strain, which is important for a reason that will became apparent in a moment. The WI-26 I laid down in several hundred ampoules had early population doublings, maybe sixth or seventh doubling. And this was... that number I thought would supply the world's requirements for an indefinite period of time.

It turned out that I was wrong; that within a very short period of time, the worldwide demand for the cells was such that it was almost immediately apparent in 1961, the beginning of the year I believe, that WI-26 would not last long enough, although it was by then fairly widely distributed. So, we decided to do another cell strain and because WI-26 was male, we decided to make one from a female foetus in order to assure a likely way of distinguishing between the two.

One can make those distinctions on biochemical terms today that could not be made easily at that time. And because we had the Barr bodies in the female cells, not the male cells, that would be an easy way of making a distinction if there was confusion or contamination of one cell culture with another, which was a continuing problem – still is today – in the field of cell culture; that is, contamination of one culture with cells from another.